Hidogird j'ournd
thc Z,innmn
I J ~
So&/y ( 1 988), 33: 5 1-93. With 4 figurrs
Sequential evolution of Euphilotes
(Lycaenidae: Scolitantidini) on their
plant host Eriogonum (Polygonaceae:
Eriogonoideae)
OAKLEY SHIELDS
4890 Old Highway, Mariposa, California 95338 and Department of Entomology, Los
Angeles County Museum of Natural History, Los Angeles, CA 90007, U.S.A.
AND
JAMES L. REVEAL F.L.S.
Department o f Botany, University o f Maryland, College Park, Maryland 20742, U.S.A.
Receimd I I February 1987, accepted f o r publication 20 July 1987
T h e relationship between the butterfly genus Euphiloles and their host plant genus Eringnnum in
western North America is suggested to be one of sequential evolution rather than coevolution.
Eriogonum, a genus of nearly 250 specks, probably had a Miocene origin, but has had its modern
distribution significantly influenced by recent Pleistocene glaciation. T h e evolution of Euphilotes, as
a distinct genus of four sibling species, apparently postdates the establishment and recent
proliferation of Eriogonum. Successful speciation in Euphilotes has been accomplished mainly through
modifications in genitalia of those butterflies using a single species of Eriogonum. T h r subsequent
proliferation of Euphilotes subspecies has been the result of host switching coupled with geographic
isolation onto individual species of Erzogonum acting as restricted biogeographic islands. In the first
instance, direct evolutionary competition for a limited resource (one species of Eriogonum) leads to
partitioning of that resource by the butterflies whose entire life cyclc is associated with that plant
species. I n the second instance, host switching and isolation have permitted establishment of minor
subspecies without significant interaction with other subspecies of the same species. In instances
where interspecific subspecies competition exists, resource partitioning, coupled with more
pronounced genetic isolation, seem to have occurred resulting in more readily distinct subspecies.
\.Ye speculate that the success of subspeciation in Euphilotes is dependent upon the numeric size and
geographic extent of the host species. Euphilotes subspecies on plants of restricted distributions are
themselves seemingly limited in their evolutionary potential as the most dynamic cvolution of
Eiiphifotes subspecies is that associated with widespread and variable Eringonum species. I n all
instances, the tempo and mode of evolution in Euphilotes appears to be sequential as it follows and is
seemingly dependent upon what has already occurred in Eriogonum.
K E Y W O R D S : Butterflies wild buckwheat - sequential evolution - coevolution
Euphilotes Lycaenidae - Eriogonum Polygonaceae.
~
-
~
~
biogeography
~
CONTENTS
Introduction .
. . .
Eriogonoideae relationships
Scolitantidini relationships .
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01988 'Ihe Linnean Society of London
0. SHIELDS AND J. L. REVEAL
52
Host-plant utilization .
Phylogenetic deductions
Summary. . . .
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Acknowledgements
References. . . .
Appendix. . . .
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93
INTRODUCTION
Euphilotes Mattoni is a taxonomically complex lycaenid genus of butterflies
consisting of four sibling species found in western North America (Mattoni,
1954a, 1965, 1977; Shields, 1975, 1977a, b; Fig. 1) separable primarily and
readily on male genitalic differences. These species have, in the past, been
referred to Philotes Scudder, Pseudophilotes Beuret and Shijimiaeoides Beuret, and
sometimes Philotes pallescens Tilden & Downey, Philotes spaldingi Barnes & McD.
and Philotes mojave Watson & W. P. Comstock have been considered separate
species. Only rarely, however, have the appropriate valid combinations been
proposed in the above genera in accordance with the provisions of the
International Code o f zoological Nomenclature (Ride, Sabrosky, Bernardi & Melville,
1985). The four species, E. rita (Barnes & McD.), E. enoptes (Bdv.), E. battoides
(Behr) and E. bernardino (Barnes & McD.), include 27 named subspecies
(Table 1) that are often specific to particular species of wild buckwheat
(Eriogonum Michx.-Polygonaceae, a family of 40 genera and about 900 species,
subfamily Eriogonoideae with 14 described genera and about 330 species, 247
belonging to Eriogonum; Table 2, Fig. 2), a genus found mainly in western North
America (Reveal, 1969a, b, 1978; Reveal & Howell, 1976).
E. battoides centralis
E. bemardino "E. Mojave"
I
E. banoides corntochi
E. battoides oregonensis
E. bemardino mariini
.I
E. bemardino bemardino
E. battoides tntermedia
I
E. bemardino altyni
E. enoptes bayensis
I .
E. rita nta
I
E. rita coloradensis
I
1
E. rita emmeli
E. rita-
E. rita pallescens
I
E. rita mattonii
Figure 1. Phylogenetic relationships of the species and subspecies of Euphilotes.
SEQUENTIAL EVOLUTION OF EUPHILOTES ON ERIOGONUM
53
TABLE1. Distribution a n d nomenclatural transfers of Philotiella a n d Euphilotes a n d their
subspecies*
Name
Philotiella speciosa (Hy Edwards) 1876. Proc. Calif.
Acad. Sci. 7: 173 (n. comb.)
P. speciosa speciosa
P. speciosa bohartorum (Tilden) 1967. J. Res. Lepid. 6:
281-284 (n. comb.)
Euphilotes rita (Barnes & McD.) 1916. Canad. Ent.
48: 223-224 (n. comb.)
E. rita mattonii (Shields) 1975. Bull. Allyn Mus. 28:
20-21 (n. comb.)
E. rita pallescens (Tilden & Downey) 1955. Bull. S.
Calif. Acad. Sci. 54: 25-29 (n. comb.)
E. rila eluirae (Mattoni) 1965 [1966]. J. Res. Lepid.
4: 94-99 (n. comb.)
E . rita emmeli (Shields) 1975. Bull. Allyn Mus. 28:
16-20 (n. comb.)
E. rita coloradensis (Mattoni) 1965. J. Res. Lepid. 4:
81-102 (n. comb.)
E. rita rita
Euphzlotes enoptes (Boisduval) 1852. Ann. SOC.Ent.
France (2) 10: 298-299 (n. comb.)
E. enoptes dammersi (Comstock & Henne) 1933. Bull.
S. Calif. Acad. Sci. 32: 23-26 (n. comb.)
E. enoptes spaldingi (Barnes & McDunnough) 1917.
Contr. Natural Hist. Lepid. N. Amer. 3: 214216,
262, 264 (n. comb.) (syn. pinjuna Scott)
E. enoptes Iangstoni (Shields) 1975. Bull. Allyn Mus.
28: 23-24 (n. comb.)
E. enoptes enoptes
E. enoptes mojaue (Watson & W. P. Comstock) 1920.
Bull. Amer. Mus. Natural Hist. 42: 455-456 (n.
comb.)
E . enoptes tildeni (Langston) 1963 [1964]. J. Lepid.
Sac. 17: 212-216 (n. comb.)
E. enoptes bayensis (Langston) 1963 [1964]. J. Lepid.
Sac. 17: 208-212 (n. comb.)
E. enoptes smithi (Mattoni) 1954. Bull. S. Calif. Acad.
Sci. 53: 160-162, 165 (n. comb.)
Distribution
Southern and western Nevada south through
southern California to Baja California Norte and
extreme south-western Arizona
Near Briceburg, Mariposa Co., California
Elko Co., Nevada
Tooele, Juab and Washington Cos., Utah, westward
to Elko Co., Nevada, thence across central
Nevada to Mono Co., California
Extreme southern Mono Co., California southward
through Inyo Co. along the western margin of the
Mojave Desert in Kern, Los Angeles and San
Bernardino Cos
South-eastern Utah and north-eastern Arizona to
San Juan Co., New Mexico, and Montezuma
Co., Colorado
Extreme southern Wyoming south into northeastern and south-central Colorado
Central and south-eastern Arizona east across southwestern New Mexico to extreme western Texas
Southern California eastward to south-eastern
Nevada (also Newberry Mountains, Clark Co.,
Nevada) and western Arizona
Eastern Nevada (Lincoln and White Pine Cos.) to
western Utah east to south-western Colorado
south to northern Arizona and north-western
New Mexico
Inyo and San Bernardino Cos., California
Southern Oregon south to southern California and
extreme western Nevada; disjunct in south-central
Washington
Deserts of southern California from Inyo Co. to
Riverside Co. east across north-eastern Clark Co.,
Nevada to southern Kane Co., Utah
Southern Coast Ranges of central California from
Monterey and Stanislaus Cos. south to Kern and
Ventura Cos.
Northern Coast Ranges of California from San
Mateo, Contra Costa and Solano Cos. north to
Humboldt Co
Coastal Monterey Co. and Mt. Loma Prieta, Santa
Cruz Co., California
0. SHIELDS AND J. L. REVEAL
54
‘rABLE
1 -continued
Name
Distribution
6. moI)/p.r nnrilla (Barnes & McDunnough) 1918.
Contr. Natural Hist. Lepid. N. Amer. 4: 77-79
111. comb.,
Western and northern Nevada north to southeastern Oregon and south-western Idaho east
across northern Utah to western Colorado,
Wyoming and Montana. Also Cypress Hills,
Alberta, and Val Marie and Rosefield,
Saskatchewan, Canada
Northern Oregon and central Washington
E.
columbine [Mattoni) 1954. Bull.
P ~ { J ~ S
S.Calif:
Acad. Sci. 53: 162-165 ( n , comb.)
E. hafluides (Bchr) 1867. Proc. Calif. Acad. Sci. 3:
282 In. comb.)
B. ha//oides glaucon (Hy. Edwards) 187 1. Trans.
Anicr. Enr. Sor. 3: 210 ( n . comb.)
E.
hnttoideJ baueri (Shields) 1975. Bull. Allyn Mus.
28: 1 5 ~16 jn. comb.)
B. hnftoides haltoides
E. baltoides infermedia (Barnes & McDunnough)
1917. Contr. Natural Hist. Lepid. N. Amer. 3:
214, 262 (n. comb.)
8.hatloides comstocki (Shields) 1975. Bull. Allyn Mus.
28: 12 (n. comb.)
Eastern California and western Nevada north into
south-western Idaho and through Oregon and
Washington to extreme southern British
Columbia, Canada
Western Nevada and Lincoln Co., Nevada, to Inyo
Co., California
Sierra Nevada of California from Fresno Co. north
to Sierra Co
Northern montane California (as far south as
Tuolumne Co.) and in Carson City, Douglas and
Washoe cos., Nevada
Eastern Kern and south-eastern l u l a r e Cos.,
California (possibly disjunct in Summit Co..
Utah)
E. hattoides ortgunensis (Barnes & McDunnough)
1917. Contr. Natural Hist. Lepid. N. Amer. 3:
214. 262 (n. comb.)
E. ha1toide.i centralis (Barnes & McDunnough) 1917.
Contr. Natural Hist. Lepid. N. Amer. 3: 214-215,
262 (n. comb.)
E. bernnrdino (Barnes & McDunnough) 1916. Contr.
Yatural Hist. Lepid. N. Amer. 3: 116-117, 152
;stat. et comb. nov.)
E. brnrardino bernardino
Klamath Co., Oregon
E. bernardino allyni (Shields) 1975. Bull. Allyn Mus.
28: 10--I1 in. comb.)
8.bernardino mnrlzni (Mattoni) 1954. Bull. S. Calif.
Acad. Sci. 53: 157-160, 164 (n. comb.)
E. hernardino ellisii (Shields) 1975. Bull. Allyn Mus.
28: 12-14 in. comb.)
Coastal Los Angeles Co., California
Mountains of south-western Colorado and northcentral New Mexico to Gila Co., Arizona;
disjunct in Modoc Co., California
Northern Baja California northward through
southern California to Monterey, San Benito,
Stanislaus and Inyo Cos., and in western Nevada
to Churchill Co
South-eastern California and south-central Nevada
(also in Lincoln Co.) east to westrrn Arizona.
Eastern Utah south to northern Arizona and Mesa
Co., Colorado
*Although Mattoni ( 1977j validly proposed both Euphilotes and Philotiella according to the International Code
~Jzoological .Vomenclature (Ride el al., 1985), he failed to make the necessary transfers. These are made here by
Shields.
This extreme host specificity makes it ideal to study host-animal sequential
evolutionary development in line with the ‘caterpillars as botanists’ theory
(Forbes, 1958) as the entire life cycle of these colonial, sedentary lycaenids
(nectar feeding, mate-seeking and mating, oviposition and larval development)
is confined to Eriogonum (Shields, 1975). Being sedentary, Euphiloks is greatly
SEQUENTIAL EVOLUTION OF EUPHILO TES O N ERIOGONUM
'rABLE
Name
55
2. Synopsis of Eriogonoideae
Species
n
Distribution
Eriogonum
annual
biennial
perennial
247
20
North America from extreme east-central Alaska
south to central Mexico, and from the islands
off the coast of California and Baja California
east to Florida, the Carolinas and the
Appalachian Mountains
Eucyrla
perennial
105
16, 18, 20, 40
Western North America and north-central
Mexico; mainly in the Rocky Mountains and
Intermountain West
20
Great Plains from extreme south-rentral Canada
south to extreme northern Mexico
Clastomyelon
perennial
20
Endemic to the Death Valley area of southeastern California
Eriogonum
perennial
20
Southern United States from the Carolinas south
to Florida west to Kansas, New Mexico,
Texas and extreme northern Mexico
Alaska and western Canada south to California,
north-central Mexico and northern Texas
with an isolated species in Virginia and U'est
Virginia
Micrantha
annual
biennial
2
Oligogonum
perennial
31
16, 20, 38, 40
Pterogonum
perennial
11
16, 20
Rocky Mountains of Wyoming and Nebraska
south to north-central Mexico, west to Utah
and Arizona
Ganysma
perennial
annual
60
16, 18, 20, 40
Desert regions of western North America from
southern Canada to northern Mexico
Oregonium
annual
35
9, 11, 12, 17,
18, 20
Mainly California but from south-western
Canada south to north-western Mexico east
across Utah and Colorado to Texas and
northern Mexico
Dedeckera
perennial
20
Last Chance, White and Panamint mountains,
Inyo County, California
Ovtheca
annual
20
Western U.S.A. and Chile
Goodmania
annual
20
South-eastern California
Stenogonum
annual
20
Intermountain West from south-western
Wyoming south through Colorado and eastern
Utah to northern Arizona and adjacent New
Mexico
Hollisteria
annual
21
Central California
Nemacaulis
annual
-
Southern California and Arizona south to
northern Baja California and Sonora, Mexico
0. SHIELDS AND J. L. REVEAL
56
TABLE
2--continued
n
Distribution
1
20
Death Valley region, California
50
19, 20, 40
Mucronea
annual
2
19,zo
Cenlrostegia
annual
4
20
Lastarriaea
annual
2
20, 30
Harfordia
perennial
1
-
Peninsular Baja California, Mexico
Pterostegia
annual
1
14
Oregon and California south to Baja California,
Mexico east to Utah and Arizona
Name
Gilmania
annual
Chorizanthe
annual
perennial
Species
Western North America (mainly in California;
annuals only) and in Chile ( 6 perennial, 1
annual species)
Western and southern California
Central and southern California east to Arizona
and south-western Utah
California and Baja California, Mexico, and
Chile
affected by isolation and extinction (Austin & Murphy, 1987). Evolutionary
trends in Euphilotes are evident since there has been preservation of intermediate
stages in some cases. There were probably many evolutionary advancements via
punctuated events of ‘major jumps’ (i.e. gaps in the evolutionary development
of their hosts). The food choice of Euphilotes on Eriogonum has unmasked direct
evolutionary links, with the butterflies evolving directly as a result of switches in
host plant preferences coupled with geographic and habitat isolation, a
phenomenon Benson, Brown & Gilbert (1975) demonstrated in the heliconian
butterflies. They found the most primitive heliconians used the most ancient
members of the plant family Passifloraceae, with the more advanced heliconians
Gwdmania
Gihania
oxyrhecrr
Cenrmstegia
Figure 2. Phylogenetic relationships of the Eriogonoideae.
SEQUENTIAL EVOLUTION OF EUPHILO TES ON ERZOGONUM
57
on the more recently radiated taxa. The same is true for Euphilotes and
Eriogonum.
Eriogonum is found in western North America from east-central Alaska to
central Mexico eastward, becoming less common on the Great Plains and
infrequent in the eastern United States from West Virginia, south to northern
Florida. Euphilotes is restricted to the southern and western part of this range
where Eriogonum is common in terms of species numbers and abundant in terms
of individuals. The southern extension of Eriogonum and Euphilotes corresponds
with the southern boundary of the Nearctic faunal realm (see Rapoport, 1971),
but Euphilotes is not known from the northern or eastern part of the range of
Eriogonum, and, even in the south, this lycaenid genus is lacking when the
diversity and abundance of its host decreases. Euphilotes flight period is
synchronized with Eriogonum blooming time. Adults are often common but
probably have little or no significance in pollination. Further, fully 70% of the
Euphilotes subspecies occur in California where Eriogonoidae has its greatest
concentration of genera (only Stenogonum and Hal-fordia are not found in the
state). Similarly, 78% of the subspecies of Apodemia mormo, another user of
Eriogonoideae, reside there too (Opler & Powell, 1961; Stanford, 1973). Thus,
the Californian habitat (no matter its location in the geologic past) has been
significant in the evolution of Eriogonoideae, and in recent times in the
evolution of subspecies of Euphilotes and Apodemia.
The subspecies of each Euphilotes species are primarily allopatric. Particularly
useful here are the concepts of host plants as islands in evolutionary time (see
Brown & Gibson, 1983; Janzen, 1968; Opler, 1974; Kuris, Blaustein & Alio,
1980), sequential evolution (Jermy, 1976), race formation from host plant
change (Heydemann, 1943; Jaenike, 1981), and population regulation via
temporal dissociation (Clench, 1967). Race formation could also occur as a
result of geographical, topographical and ecological isolation (Thorpe, 1945),
by genetic isolation in peripheral founder populations (Grant, 1982), and by
divergence along with their hosts and by ‘jumps’ to new hosts (Savile, 1971).
Host plants have been used as a taxonomic tool in classifying Semanophorinae
(Sphingidae) and Pieridae (Harris, 1972; Meeuse, 1973).
In ‘sequential evolution’, the evolution of the phytophagous insects follows or
lags behind the evolution of their host plants, with the insect evolution not
appreciably influencing the host plant evolution (Jermy, 1976). Regional
climates set limits for all plants and animals, yet geologic and geographic factors
combine to propel plant evolution (Kruckberg, 1986), and thus creating a
diversified trophic base for the evolution of specialized phytophagous insects. In
this case, the players are Eriogonum and Euphilotes. ‘Coevolution’ or ‘reciprocal
evolution’ does not appear to be a significant factor here such as sometimes
occurs in pollination systems. Once the host plant diversifies, it becomes
analogous to an ‘island’ in evolutionary and contemporary time for the insects
feeding upon it.
Jermy (1984, with an extensive bibliography) builds a strong case for the lack
of coevolution between plants and phytophagous insects (with figwasps and figs
a unique exception) and proposes sequential evolution as the best explanation
for most all insect/host plant relationships. The evolution of phytophagous
insects follows that of plants without affecting plant evolution. The structural
and biochemical diversity of angiosperms provides a profusion of niches for the
58
0. SHIELDS AND J . L. REVEAL
evolutionary radiation of their insects, while the selection pressure from insect
attacks is weak or lacking. T h e coevolutionary theory of Ehrlich & Raven
( 1965), though the most generally accepted theory of the evolution of specific
insect/host plant relationships, is based on speculation and does not stand up to
factual analysis.
ERIOGONOIDEAE RELATIONSHIPS
Erzogonum is a group of annual or perennial herbs or shrubs; one species,
E. annuurn Nutt.-in portions of its range-is a biennial, and E. alaturn Torr. in
Sitgr. is a monocarpic perennial. Some insular shrubs may become rather large,
and while not truly arborescent, may dominate the habitat of wind-swept
iclands (e.g. E. giganteum S. Wats. or E. arborescens Greene). Individuals of this
genus occur from along the immediate coast of California where subjected to
sea-spray to the highest elevations in the Sierra Nevada; others occur in the
deserts of Death Valley below sea-level, the ‘bad lands’ of the Dakotas, the shale
barrens of the Appalachian Mountains, and the volcanic pumice sands of Crater
Lake.
The genus is divided into eight subgenera and numerous sections (Reveal,
1969a, b; see Table 2 ) . Three major lines of evolutionary development have
occurred. It is thought the basic unit of Eriogonum is represented by the subgenus
Eucycla (Nutt.) Kuntze in Post & Kuntze, the largest of the subgenera with
some 105 perennial species of herbs and shrubs widespread in western North
America. From that evolved such other subgenera as the bitypic Micrantha
(Nutt.) Reveal in Gunckel (E. annuum and E. multiforum Benth.) of the Great
Plains, the monotypic Clastomyelon Cov. & Morton ( E . intrafractum Cov. &
Morton) of Death Valley, and the predominantly annual subgenera of
Ganysma (S. Wats.) Greene (60 species) and Oregonium (S. Wats.) Greene (35
species) of the arid West and coastal California and Mexico, respectively. A
second line of development involved the bitypic subgenus Eriogonum
( E . tomentosum Michx. and E. longifolium Nutt.) of the southern and eastern
United States and the predominantly western subgenus Oligogonum Nutt. (31
species). The third line is characterized by the subgenus Pterogonum (H. Gross)
Reveal ( 1 1 species) mainly of northern Mexico and the south-western United
States. Pterogonum is decidedly closer to the Eucycla-Ganysma line than to the
Eriogonum-Oligogonum line.
For the most part, species of Eriogonum occur in arid and semi-arid regions.
Many are narrowly restricted in their distribution and there are numerous local
endemics. This is particularly true of the matted or cespitose perennials
belonging to the subgenus Eucycla, although none is used by Euphilotes. Among
the perennial herbs and shrubs, several are widely distributed and frequently
divisible into local, geographic varieties that are themselves narrowly endemic.
While many annual species may be equally restricted, several are widespread
and in fact sometimes weedy.
As noted above, Eriogonum is restricted to North America although
E. divaricatum Hook. was found in Argentina (Reveal, 1981) during the growing
season of 1900-1901; it has not been rediscovered since and is regarded here as
an accidental introduction. Three related genera, Chorizanthe R . Br. ex Benth.,
Oxytheca Nutt. and Lastarriaea are native to North and South America. Oxytheca
SEQUENTIAL EVOLUTION OF EUPHIL,O TES O N ERIOGOJWIM
59
dendroidea Nutt. subsp. chilensis (Remy in Gay) Ertter and L. chilensis Remy in
Gay are both found in Chile and/or Argentina as are about nine species of
perennial Chorizanthe. The one Chilean annual of Chorizanthe, C. commisuralis
Remy in Gay, is closely related to the most widespread North American annual,
C. brevicornu Torr., and its time of arrival in South America is probably
compatible with that of the other annuals. The South American annuals of
Oxytheca and Chorizanthe occur in desert habitat similar to their counterparts in
North America, while L . chilensis, like its northern relative, L. coriacea
(Goodman) Hoover, occurs mainly along the immediate coast.
Oxytheca (seven species; Ertter, 1980) and Chorizanthe (50 species; Goodman,
1934) are rather widely distributed in North America in the western United
States and Baja California, Mexico. Stenogonum Nutt. (bitypic; Reveal & Ertter
197713) is restricted to the northern Colorado River drainage basin from
Wyoming south to Arizona and New Mexico, while Centrostegia Gray ex Benth.
(now considered to consist of four species, but three of these represent monotypic,
but as yet undescribed genera; Goodman, 1957) is a coast range and warm
desert genus that occurs from southern California eastward to Utah and south
to northern Mexico. The range of Nemacaulis Nutt. (monotypic; Reveal &
Ertter, 1980) is found mainly on the warm deserts of southern California and
northern Baja California Norte, although it will occur on the immediate coast,
much like Lastarriaea (two species; Goodman, 1943). Several, mostly monotypic,
genera are endemic to California: Dedeckera Reveal & Howell (1 976), Goodmania
Reveal & Ertter (1977a), Gilmania Coville (1936), Mucronea Benth. in DC.
(bitypic) and Hollisteria S. Wats. The latter two occur mainly in the Coast
Ranges while the others inhabit inland desert areas.
The origin of the subfamily Eriogonoideae is unknown and its relationship to
the rest of Polygonaceae is obscure. Even the relationship of Polygonaceae to
other families of flowering plants (Magnoliophyta) is dubious. Cronquist ( 1981 )
and most other students of the phylogeny of Magnoliophyta continue to place
the family in its own order, Polygonales (see Bedell & Reveal, 1982), near the
Caryophyllales, but none is pleased. The relative isolation of Polygonaceae was
confirmed by Rodman et at. (1984) who concluded that Polygonaceae are only
weakly related to the Caryophyllales. The earliest pollen records for the
Caryophyllales date from mid-Maestrichtian of the uppermost Cretaceous while
the earliest Polygonales pollen does not appear until the middle of the Paleocene
(Nowicke & Skvarla, 1977; Muller, 1981). O n this and other evidence,
Polygonales are most likely of a recent origin, but from what ancestral group
they arose is unknown.
T h e subfamily Eriogonoideae (Table 2) and the genus Eriogonum probably
came into being during the Miocene Era [we are following Savin (1977) in our
dating of geologic eras] as a group of perennial shrubs with a diploid
chromosome number of n = 10. The number of species and extent of their
distribution cannot be determined. During the period of early differentiation,
the genus divided into two major segments, one culminating in the present-day
genus Eriogonum and the other in the genus Chorizanthe. As perennial shrubs and,
by the time that Chorizanthe evolved, perennial herbs, these plants probably were
found in the more arid grassland and shrub regions of North America,
successfully adapting to the drying trend that continued into the Pliocene
(Axelrod & Raven, 1985). During the Late Miocene and especially during the
60
0. SHIELDS AND J. L. REVEAL
Pliocene, Eriogonum and Chorizanthe underwent rapid and explosive evolutionary
differentiation, producing an array of new genera, essentially all of which were
associated with the annual habit. Chorizanthe itself was so successful in this that
all of its perennial ancestors in North America were lost, leaving only a trace of
their previous existence in the warm deserts of Chile (Reveal, 1978).
The rapid development of arid regions in the American West during the
Pliocene resulted in such new genera as Oxytheca, Stenogonum, Hollisteria and
Nemacaulis in association with Eriogonum, and Mucronea, Centrostegia and Lastarraea
with Chorizanthe. During this same period of rapid expansion, there was a
continued development within Eriogonum, producing an array of both annual
and perennial subgenera. Some of these subgenera probably had their origin
during the Late Miocene, notably Oligogonum, Eriogonum and Pterogonum,
although it is possible that Oligogonum, which is used primarily by the most
advanced species of Euphilotes, may not have produced an abundance of species
until well into the Pliocene. The predominantly annual subgenus Ganysma
might have evolved from Eucycla during the Late Miocene or more likely early
Pliocene, but it is thought Oregonium probably did not differentiate until the
Pliocene. Most significantly, it is suggested that by mid-Pliocene time, all the
diploid ancestors of Eriogonum, and even early members of the genus, were
replaced by tetraploid derivatives.
A full understanding of the extant perennial Chorizanthe continues to be
illusive. As suggested by Reveal (1978), it is possible the South American
perennial Chorizanthe species are diploids, but until actual counts are made this
shall remain unknown. Raven (1963) and Reveal (1978) have suggested these
perennials were probably isolated during the Pliocene. It has now been
established that the emergence of the Central American landbridge
reconnecting North and South America occurred 5.7 million years ago, during
latest Miocene times (Emiliani, Gaertner & Litz, 1972; Raven & Axelrod, 1975;
Keigwan, 1982). As for the North American annuals belonging to Chorizanthe,
the data currently available point to these being derived tetraploids like
Eriogonum and all other extant annual genera (so far as known; see Table 2).
Some of the monotypic taxa are probably of Pleistocene origin. Eriogonum
subgenus Clastomyelon and the genera Dedeckera, Gilmania and Goodmania all
appear to have evolved recently. These plants are endemic to the Mojave Desert
of California, and a genus like Gilmania may not have become established until
the postglacial Wisconsin within the last 10000 to 12000 years (Reveal, 1980).
Tectonically, the Death Valley area, where Clastomyelon, Dedeckera and
Gilmania are all endemic, is an area formed during Pliocene and Quaternary
time (Wernicke, Spencer, Burchfiel & Guth, 1982) with Death Valley itself the
result of tension between the Panamint Range and the Black Mountains
(Burchfiel & Stewart, 1966) in association with the general deformation of the
Mojave block to the south (Garfunkel, 1974). During Late Pliocene time (2.3
m.y. B P ) , the Sierra Nevada-White/Inyo mountains block broke up and formed
Owens Valley (Bachman, 1978). With the Sierra Nevada undergoing major
uplifts (Axelrod, 1957) and major glaciation (Curry, 1966), even during the
Pliocene, it might be argued that a t least some of these taxa differentiated then.
In particular, the origin of Dedeckera eurekensis Reveal & Howell might possibly
be traced to Late Pliocene. However, because of the high number of herbaceous
plants endemic to the Death Valley region (Stebbins & Major 1965; Hunt,
SEQUENTIAL EVOLUTION OF EUPHZLOTES ON ERIOGOWUM
61
1966), it seems improbable that Gilmania (and even Goodmania) became
established during the relatively modest climatic conditions of mid-Pliocene
time. With the continued development of arid conditions into the Pleistocene,
and the rapid development of the Mojave Desert since about 12 000 BP (Wells &
Hunziker, 1976; Reveal, 1980; Thorne, 1986), it seems reasonable to assign the
origins of the annual endemic genera to Late Pleistocene or even Early
Holocene time.
Of critical importance here is the understanding that the geographical
position of the present-day flora has been altered over time, and in particular
during and since the Wisconsin glacial episode during the Pleistocene. About
25000 years ago, the current flora of the Intermountain Region, for example,
was considerably further to the south, and the Mojave Desert did not exist (see
Raven & Axelrod, 1978; Reveal, 1980; Axelrod & Raven, 1985 where numerous
papers on this subject are cited). However, not all populations of every species
were forced southward, rather many moved elevationally down slope. In the
Sierra Nevada, plants likely remained on the ridges above the effects of glaciers
in the canyons whereas others moved out onto the lower flats below the ice. In
the Intermountain Region and in the many valley systems in and around Death
Valley, the valley bottoms were filled with pluvial lakes restricting the extent to
which species could occupy the lower elevations. Thus it was that many species
likely had highly restricted distributions in the recent past where today they are
rather common.
Some species of critical importance to our discussion here are found on
moving sands that have come into existence only after the pluvial Lake
Lahontan and Lake Bonneville dried up. An example would be Eriogonum
nummulare M. E. Jones (previously called E. kearneyi Tidestrom), a species that
occurs on moving sands and sand dunes at or elevationally below the lake
shores. In south-eastern Utah and adjacent parts of Colorado, New Mexico and
Arizona, the mesas were not subjected to flooding, and here populations of
E. corymbosum Benth. in DC. and E. leptocladon Torr. & Gray probably existed,
but perhaps not in the densities suitable for survival of Euphilotes.
It seems reasonable to argue here that Eriogonum microthecum, on the other
hand, probably was abundant in the glaciate regions of the American West,
with the var. laxijorum Hook. being widespread in the cooler regions. Similarly,
the var. simpsonii (Benth. in DC.) Reveal (1983)-previously called var. foliosum
(Torr. & Gray) Reveal-probably
was equally widespread in the warmer
regions in what is today southern Arizona and California. It would be most
useful to know the exact identity of the fossil E. microthecum leaves found in
wood-rat middens from three Mojave Desert sites reported by Wells and Berger
(1967) as being 9140+ 140, 9320+300 and 10 loo+_160 BP. It is possible those
found near Mercury, Nevada, would prove to be var. laxijorum given the
associated species. Eriogonum wrightii Torr. ex Benth. in DC. probably was
widespread too, and occupied not only much of the same region it does today in
Arizona, New Mexico and Mexico, but was far more common. The existence of
higher elevation varieties in the mountains of California and Baja California
portend of an ability to occupy cooler regions, and the large, shrubby
varieties of Baja California and southern Arizona and California reveal the
extent to which this species can adapt to extremely arid conditions.
Even the higher elevation and more northern species of the subgenus
62
0. SHIELDS AND J. L. REVEAL
Oligogonum, notably Eriogonum umbellatum Torr., E. heracleoides Nutt., E. jamesii
Benth. in DC. and E.ftauum Nutt. in Fras. must have occupied much lower
elevations during the last glacial period. Some populations of these species
remained in situ, but others migrated down slope and to the south. Certainly the
isolation of E.jamesii var. wootonii Reveal in southern New Mexico or E.Jlauum
var. aquilinum Reveal in HultCn in the non-glaciated regions of east-central
Alaska---not to mention E. allenii S. Wats. in Virginia and West Virginiaattest to a much wider, and probably more common, distribution in the past
than is the case today.
As we shall discuss below, the evolution of subspecies in Euphilotes can be
traced to the responses of Eriogonum to climatic changes and must be examined
in light of the floristic movements during Late Pleistocene and Holocene times.
The two most phylogenetically isolated genera in the subfamily
Eriogonoideae, the perennial Harfordia Greene & Parry of Baja California, and
the annual Pterostegia Fisch. & Meyer of Oregon south to northern Mexico,
probably evolved from pre-Eriogonum ancestral types during the Miocene,
although this needs to be confirmed by cytological studies. T h e unusual
chromosome number of n = 14 for Pterostegia is markedly distinct within
Eriogonoideae, and the bladdery, inflated fruits of Harfordia are otherwise
unknown. Certainly the time and point of origin for Harfordia is a matter of
some concern. For example, could this be a highly evolved, greatly modified
form that is representative of the lost North American perennial Chorizanthe line?
T h e perennial South American Chorizanthe species can trace their origin to one
(or at most) two ancestral types that were successfully introduced from North
America, b u t we believe Chorizanlhe at one time probably consisted of several
diverse perennial expressions. If Hurfardia is the culmination of one of those lines
of development, its placement within the subfamily would have to be altered to
a position much closer to Chorizanthe than expressed currently (Reveal &
Howell, 1976).
It would seem, then, that by mid-Pliocene time, some 3 m.y. B P , Eriogonum,
Chorizanthe, and most likely several of their satellite genera, were well established
with numerous species rapidly evolving and the distribution of each taxon
expanding. We suspect that the subsequent evolution of such genera as
Dedeckera, Gilmania and Goodmania owe their limited patterns of distribution to
both their restricted ecological (especially edaphic) requirements and their
recent origins.
SCOLITAN‘I’IDINI RELAIIONSHIPS
T h e Holarctic Scolitantidini ( = Glaucopsychidi) ( 16 genera; Table 3 ) , to
which Euphilotes belongs, has its greatest radiation in western Szechwan of
central China, where numerous genera are concentrated (Mattoni, 1977).
Philotiella Mattoni (south-western North America), Shijimiaeoides (Korea, Japan
and isolated in western Szechwan), and Pseudophilotes (Palearctic and North
Africa) have all been considered potential ancestors to EuphiloteJ (Mattoni,
1954b, 1977; Shields, 1975, 1977a). Based on gross morphology Shijimiaeoides
and Pseudophilotes would qualify equally as the ancestral genus for Euphilota.
However, Euphilotes feeds on Eriogonum, a host plant that occurs primarily in
xeric habitats more similar to those of the host plants used by Pseudophilotes than
SEQUEN’I‘IAL EVOLUTION OF EUPHILO TES ON ERIOGONUM
63
TABLE
3. Distribution of Euphilotes and relatives
Name
Distribution
Paleophilotes triphysina
Montane in southern Russia (Kazakhstan,
Kirgiz) and north-west China (Sinkiang,
Chinghai)
Deserts of north-eastern Iran to south-western
Russia (Turkmen, Kazakhstan), and Tyan
Shan in north-west Sinkiang, China
Montane Afghanistan (Koh-i-Baba Mountains,
3600-4000 m elev.)
Deserts and occasionally montane regions of
southern California (also Mariposa Co.),
central and southern Nevada extreme south
western Arizona, and northern Baja California,
Mexico (a single known population)
Primarily in deserts of south-west Texas, western
New Mexico, Colorado, extreme southern
Wyoming, Utah, central and north-central
Nevada, northern, central and eastern
Arizona, and the western edge of the southern
California deserts
Montane or occasionally desert regions of
California, west-central Arizona, Nevada,
Utah, western Colorado, Sioux Co. Nebraska,
extreme western Wyoming, extreme southcentral Montana, extreme south-eastern
Idaho, central Washington, northern and eastcentral Oregon, and occasionally in Alberta
and Saskatchewan, Canada
Northern and eastern California and central and
north-eastern Oregon to central Washington
and extreme southern British Columbia,
Canada, thencc east to south-western Idaho
(with an isolated population at Sula,
Montana), eastern Utah and across northern
Arizona and western and central Nevada to
south-western Colorado and north-central
New Mexico
Cedros Island and Baja California, Mexico
northward through southern California to
Stanislaus and Inyo Cos., thence to westcentral and southern Nevada to western and
northern Arizona, eastern Utah, and Mesa
Co., Colorado
Praephilotes anthracias
.Micropsyche ariana
Philotiella speciosa
( 2 subspecies)
Euphilotes rita
(6 subspecies)
Euphilotes enoptes
(10 subspecies)
Euphilotes battoides
(7 subspecies)
Euphiloles bernardino
(4 subspecies)
the more temperate-adapted Shijimiaeoides (see Tables 4, 5). I n terms of
morphological size, Pseudophilotes approaches Euphilotes whereas Shijimiaeoides,
which is nearly twice as large, is closer to Maculinea van Eecke in both size and
true relationship. T h e genitalic and phenotypic similarities shared by
Pseudophilotes and Euphilotes are suggestive of a close relationship. However, the
genitalia of Pseudophilotes has produced labides which are lacking in Euphilotes,
and this suggests that the gross similarities are due to convergent evolution (see
Shapiro, 1978). Also, the Eriogonum phylogeny and their chromosome pattern
suggests rita is the most primitive Euphilotes, while it is E. enoptes that
Shijimiaeoides resembles in genitalia. Philotiella genitalia, being nearest to E. rita,
64
0. SHIELDS AND J. L. REVEAL
TABLE4. Summary of host plants for Zizeerini, Brephidiini and
Scolitantidini
ZIZEERINI
Euphorbiaceae (Dilleniidae, Euphorbiales)
Euphorbia-Zizeeria knysna Trimen
Amaranthaceae (Caryophyllidae, Caryophyllales)
Amaranthus-Zizeeria knysna Trimen
Molluginaceae (Caryophyllidae, Caryophyllales)
Glinus-Zizeeria knysna Trimen
Fabaceae (Rosidae, Fabales)
Many genera-&ula
hylax Fab., Zizeeria (4 sp.)
Zygophyllaceae (Rosidae, Sapindales)
Tribulus-Zizeeria knysna Trimen
Oxalidaceae (Rosidae, Geraniales)
Oxalis-Zizula hyrax Fab., Zizeeria ( 2 sp.)
Acanthaceae (Asteridae, Scrophulariales)
Many genera-Zizula hylax Fab., zizeeria maha Kollar
Boraginaceae (Asteridae, Solanales)
Heliotropum-xizeeria trochilus Frey.
Verbenaceae (Asteridae, Solanales)
Lantana-&ula
hylax Fab.
BREPHIDIINI
Bataceae (Dilleniidae, Batales)
Batis-Brephidium isophthalma H.-S.
Chenopodiaceae (Caryophyllidae, Caryophyllales)
Atriplex-Brephidium exilis Bdv.
Chenopodium-Brephidium exilis Bdv.
Exomis-Brephidium metophis Wallengren, Oraidium sp.
Salicornia-Brephidium exilis Bdv.
Brephidium isophthalma H . 3 .
Salsola-Brephidium exilis Bdv.
Suaeda-Brephidium exilis Bdv.
Aizoaceae (Caryophyllidae, Caryophyllales)
Sesuvium-Brephidium exilis Bdv.
Brephidium isophthalma H.-S.
SCOLITANTIDINI
Polygonaceae (Polygonidae, Polygonales)
Chorizanthe-Philotiella speciosa (Hy. Edw.)
Eriogonum-Philotiella speciosa (Hy. Edw.)
Euphilotes (4 sp.)
Oxytheca-Philotiella speciosa (Hy. Edw.)
Crassulaceae (Rosidae, Saxifragales)
Dudleya-Philotes sonorensis F. & F.
Sedum-Scolitantides orion Pallas
Rosaceae (Rosidae, Rosales)
Sanguisorba--Maculinea
Fabaceae (Rosidae, Fabales)
Alhagi-Praephilotes anthracias Christ.
Colutea-Iolana ( 2 sp.)
Lupinus-Glaucopsyche bgdamus Dbldy.
Phaedrotes piasus Bdv.
Sophora-Shijimiaeoides diuina Fixsen
Many genera-Glaucopsyche (4 sp.)
Gentianaceae (Asteridae, Gentianales)
Gentiana- Maculinea
Lamiaceae (Asteridae, Solanales)
Isodon-Maculinea
Saluia-Sinia bavius Eversmann
Thymus- Maculinea
Pseudophilotes (4 sp.)
SEQUENTIAL EVOLUTION OF EUPHILOTES ON ERIOGONUM
65
TABLE5. Summary of Zizeerini, Brephidiini and
Scolitantidini on Polygonales and Caryophyllales
Plant family
Caryophyllales
Chenopodiaceae
Amaranthaceae
Aizoaceae
Molluginaceae
Polygonales
Polygonaceae
Butterfly genus
Brephidium, Oraidium
{izeeria
Brephidium, {izeeria
Zizeeria
Philotiella, Euphilotes
is further indicative of the primitive nature of rita. Of the E. rita subspecies,
mattonii (Shields) is nearest in size and appearance to Philotiella speciosa. Philotiella
speciosa and most E. rita subspecies are confined to deserts, unlike other
Euphilotes. Thus the evolutionary tendency was from summer to spring flight and
an increase in overall elevation.
The smallest Scolitantidini occur in three monotypic genera (Paleophilotes
Forster, Praephilotes Forster, Micropsyche Mattoni) found in central Asia (Fig. 3 ) ,
and today these are the most primitive of the extant genera based on Cope's
Law (see Stanley, 1973). These genera, plus Turanana Bethune-Baker and
Pseudophilofes abencerragus nabataeus Graves, are not sexually dimorphic. The great
diversity seen among the genera found in western Szechwan (see Mattoni, 1977)
is among species that are larger and more specialized, being derived perhaps
from a Turanana ancestor. T h e initial radiation from these central Asian genera
was probably across a Neogene Bering land bridge, with Philotiella (Fig. 4),
Euphilotes, and Philotes evolving subsequently in a habitat similar to that found
today in south-western North America.
Ik
Figure 3. Central Asian distribution of the three small, primitive, monotypic Scolitantidini genera,
Paleophilotes (stars), Praephilotes (circles) and Micropsyche (half circle). Praephilotes also occurs in Syr
Darya and Kirghiz Steppe, Turkestan, U.S.S.R.
66
0. SHIELDS AND J . L. REVEAL
F i p w 4. Distribution of Philotidla in the south-western U.S.A
Many of the world’s smallest butterflies are found in genera belonging to
three of the tribes of the subfamily Polyommatinae: Zizeerini (zizula Chapman,
Zizeeriu Chapman, Famegana Eliot), Brephiidini (Brephidium Scudder, Oraidium
Bethune-Baker) , and Scolitantidini (Paleophilotes, Praephilotes, Philotiellu,
Micropsyche). The genus Actizera Chapman does not fit morphologically into
either Zizeerini or Scolitantidini, and its placement is uncertain and probably a
case of convergence. Zizula hylax Fab. sometimes sways its body and wings from
side to side upon alighting as in Phi1oLe.r sonorensis, but aside from this behaviour
pattern, it is typical of the Zizeerini.
Forster (1938) once placed Zizeerini within the Scolitantidini, and Mattoni
( 1977) concluded that the facies of Paleophilotes and Praephilotes “are decidedly
Zizeerini”. Species of Zizeerini moved westward across Gondwanaland,
presumably during Upper Cretaceous times. Zizula occurs nearly throughout
Gondwanaland (Stempffer, 1933), while Zizeeria is confined to Old World
SEQUENTIAL EVOLUTION OF EUPHILO TES O N ERIOGONUM
67
Gondwanaland with incursions into China, western and south-eastern Tibet,
Korea, Japan, Taiwan, Melanesia, western Pakistan, Afghanistan, south-west
Soviet Union, and Iran. Zizeeria prosecusa Ersch. occurs in the Tyan Shan
Mountains and in the Turkestan region of central Asia. Such wide geographic
distributions indicate a probable ancient origin of the tribe before the breakup
of Gondwanaland according to Beuret (1955) and Stempffer (1933, 1967). I n so
far as is known to us, the only detailed observations on mating behaviour of
species belonging to these genera is that published by Wag0 et al. (1976) for
Zizeeria .
Zizula hylax and the dryina form of Zixecria labradus Godart overlap in Java and
Sumatra and are Celastrina-like in appearance. Celastrina Tutt is in the section
Lycaenopsis adjacent to Scolitantidini according to Eliot (1973). Thus the
Zizeerini may have arisen from ancestral taxa belonging to the section
Lycaenopsis of Polyommatinae (Celastrini) in the region of Wallace’s Line. The
male genitalia are fairly similar. Chapman (1910) made some reference to the
above similarities but decided Lycaenopsis and Zizeerini were distinct and
unrelated groups. However, the similarities are striking. Celastrina has an IndoAustralian distribution with only one widespread Holarctic species.
Although Brephidiini evolved from Zizeerini, Brephidium still shares many
unique genitalic similarities with Zizula. The geographical distribution of
Brephidium (three species) encompasses South Africa, the Neotropical region, and
southern Nearctic (Kiriakoff, 1956; Kiriakoff & Stempffer, 1952).
The diagnostic male genitalia for all the Scolitantidini genera have now been
illustrated (see Williams, 1918; Hemming, 1931; Forster, 1938; Beuret, 1957,
1958; Langston, 1963; Sorensen, 1972; Shirozu, 1973; Higgins, 1975; Shields,
1975; Mattoni, 1977, 1979; Zhdanko, 1983). I n Scolitantidini, the most
primitive species possess cristae obliquae, a dentate process on the median basal
portion of the valvae: Paleophilotes, Praephilotes, Micropsyche, Pseudophilotes baton
Berg., P. vicrama cashmirensis Moore, P. sinaicus Nakamura, Philotiella, and
Euphilotes rita. I t would appear that Paleophilotes, which is exceedingly Zizeerialike in its appearance, evolved from zizeeria and gave rise to two major lineages.
The first included Praephilotes which gave rise to both Philotiella (contrary to
Mattoni, 1977) and it, in turn, Euphilotes. The second included Micropsyche,
Turanana, Philotes, Pseudophilotes and others (see Forster, 1938, and Mattoni,
1979). The Scolitantidini are almost exclusively of a Laurasian or Holarctic
distribution with its most primitive genera in montane central Asia west of the
Pamir axis.
Paleophilotes, Praephilotes, and Micropsyche are confined to the western
Turkmenian region but are lacking in Tibet, Himalayas, Mongolia, and the
western margin of the Turkmenian region. The eastern Turkmenian region is
populated by various Zizeeria species, the presumed ancestral type to
Scolitantidini. Praephilotes, the probable ancestor to Philotiella, occurs primarily
from the Turkestan Desert to the northeastern Iranian Desert and on the Tyan
Shan (Fig. 3; see Appendix).
Praephilotes anthracias Christ. is reported as ovipositing on a young leaf of Alhagi
kirghisorum Schrenk on the Kirghiz Steppe (Seitz, 1906), a legume species
(Fabaceae) restricted to central Asia (Shaparenko, 1948; Kitamura, 1960). The
genus Alhagi (five species) ranges from northern Africa to western China,
Mongolia and the southern Soviet Union where these branched, spiny
68
0. SHIELDS AND J. L. REVEAL
subshrubs or shrubs occur in arid regions often in saline places. They have deep
root systems, contain tannins, and are decidedly drought-resistant. Alhugi
kirghisorum is restricted to only a small portion of this range, although P . anthrucias
is well-encompassed by Alhagi.
HOST-PLANT UTILIZATION
Some 44 host-plant associations were established that clearly indicate general
evolutionary patterns for the four Euphilotes species (Table 6 ) ; of course, not all
species of Eriogonum could be sampled. Some 77% of the host records are for
Eriogonum species that are mutually exclusive while 23% show overlap. Only on
E. JEauum var. flavum are three of the four species encountered, albeit rarely and
never sympatrically. Three species of Euphilotes are found on E. heermannii Dur.
& Hilg., but then on differing varieties of that host. Even so two species of
Euphilotes almost never use the same Eriogonum species in the same locality,
although E. rita emmeli and E. battoides ellisii both use E. corymbosum at Keams
Canyon in Navajo Co., Arizona, and E. enoptes enoptes and E. rita eluirae both use
E. wrightii var. subscaposum S. Wats. at Harris Grade in the Piute Mountains of
Kern Co., California. The geological time theory “holds that the number of
insect species now found on host plants is a function of the age and abundance
of the hosts in geologic time” (Opler, 1974), and on the basis of this hypothesis,
E.JEavum ought to be a primitive member of Eriogonum. That it may well be,
especially given its considerable variation and range (Colorado to Alaska).
However, compared with E. microthecum, E. heermannii, E. fasciculatum and even
E. wrightii that share at least two of the four species, it would seem ‘abundance’
is far more important than ‘time’. Also, the availability of suitable
concentrations of plant hosts must have been a significant limiting factor during
Late Pleistocene times especially if one considers the observations by King
( 1976), Wells ( 1976, 1977), Van Devender, Betancourt & Wimberley ( 1984), and
Van Devender & Hawksworth (1986) who have commented on the recent ages
and extent of the Chihuahuan, Sonoran and Mojavean deserts. In fact, Van
Devender & Hawksworth state that in “the Sonoran and Chihuahuan deserts,
characterized by summer rainfall, modern desertscrub communities Apparently
did not form until the Late Holocene, about 4000 years ago,” and the modern
desert communities on the Mojave Desert did not form until about 6000 years
ago. Inasmuch as these are the very communities where many of the shrubby
species of Eriogonum are found with an abundance of Euphilotes today, it would
appear the mere presence of several species of a genus on a given host is not, in
and of itself, of any particular significance.
Euphilotes are most commonly found on species belonging to Eriogonum
subgenus Eucycla followed by species in the subgenus Oligogonum, both
perennials. The butterflies occur infrequently on species of subgenus Ganysma
or subgenus Oregonium. T o date no records of use have been noted for species
belonging to the narrowly endemic subgenus Clastomyelon, or the more eastern
subgenera Eriogonum, Pterogonum or Micrantha. Many of the wide-ranging
species of Eriogonum are differentiated into several to many varieties:
E. fasciculatum Benth., E. microthecum, E. cor3)mbosum, E. heermannii, E. wrightii,
E. kennedyi Porter ex Wats., E. nudum Dougl. ex Benth., E. ovalifoliurn Nutt., and
E. stricturn Benth., all of subgenus Eucycla; E. umbellatum, E . heracleoides,
SEQUENTIAL EVOLUTION OF EUPHILOTES ON ERIOGOHUM
69
TABLE
6. Larval food plants for Euphilotes
Eriogonum Host
n
rita-enoptes-bernardo-battoides
Subgenus Eucycla
E. microthecum
E. effusum
E. cotymbosum
E. hylophilum
E. smithii
E. leptocladon
E. nummulare
E . heermannii
E. plumatella
E. cinereum
E. parv2flium
E. fasciculatum
E. batemanii
E. shockleyi
E. elongatum
E. wrightii
E. kennedyi
E. panamintense
E. racemosum
E. nudum
E. elatum
E. ovaltjiolium
E. strictum
E. saxatile
20
20
20
20
20
20
20
X
20
X
20, 40
20
20,40
20
20
17
17
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
-
X
20
X
X
18
X
20,40
X
20, 40
X
20
20
20
X
20,40
X
X
20
20
20
20
20
X
X
X
X
X
Subg. Oligogonum
E. umbellatum
E. heracleoides
E. compositum
E. lobbii
E. sphaerocephalum
E. jamesii
E. Jlauum
E. marifolium
E. incanum
E. polypodum
X
X
X
X
16
-
-
Subg. Ganysma
E. defexum
E. rotundijotium
E. pusillum
E. renijorme
20
-
X
X
16
16
Subg. Oregonium
E. couilleanum
E. roseurn
E. dauidsonji
E . baileyi
E. nidularium
E. polycladon
17
9
20
20
20
20
Totals
X
X
X
X
16
23
9
11
E. jamesii and E. jlavum, all of subgenus Oligogonum. Euphilotes, on the
above, have themselves differentiated into a series of different populations that
are distinct at the subspecific level. This is particularly so for populations of
Euphilotes on E. fasciculatum, E . heermannii, E. wrightii, E. nudum, E. ovalifootium, and
70
0. SHIEI.DS AND J . L. REVEAL
E. umbellatum. Larvae of Euphilotes rita elvirae (Mattoni) that normally feed on
E. plumatella Dur. & Hilg., for example, would not accept E.fasciculatum under
laboratory conditions (Comstock & Henne, 1967). Significantly, many species of
Eriogonum may have developed resistance to attack by Euphilotes larvae (see
Shields, 1974a).
The primary radiation of Euphilotes occurred on perennial Eriogonum species
and secondarily on a few annuals. I t is impossible to determine the relative
points of origin for the subgenera Eucycla and Oligogonum. For example, it is
not clear from extant species if Oligogonum arose from Eucycla or both came
from an ancestral type now extinct. It is interesting, therefore, that the juncture
of overlap between E. enoptes and E. battoides should occur among the more
primitive members of the subgenus Oligogonum, namely E. umbellatum,
E. heracleoides and E. compositum Dougl. ex Benth. There is some evidence that
E. enoptes ancilla (Barnes & McD.) may have given rise to E. batloides glaucon
(Hy. Edw.) in the Jarbidge Mountains of north-eastern Nevada (Shields 1975),
and both occur on E. umbellaturn.
The principal host plant of Philotiella speciosa speciosa is Oxytheca perfliata Torr.
& Gray (Thorne, 1961; Shields, 197413). In its absence, Eriogonum rengorme Torr.
& Frkm. is commonly used. Where the two plants occur sympatrically, the
Oxytheca is preferred. Suspected hosts by association include 0. trilobata A. Gray
(Thorne, 1961) and Chorizanthe pulchella Brandegee and/or E. thurberi Torr.
(Brown & Faulkner, 1984). T h e strongly suspected host of P. speciosa bohartorum
(Tilden) is C. membranacea Benth. by association (Shields, 1974b). Eriogonum
renqorme and E. thurberi are both members of the subgenus Ganysma (its sect.
Pedunculata) while the two just noted species of Chorzzanthe belong to very
different groups within that genus. Philotiella speciosa will also use Mucronea
calzfornica Benth. as a laboratory substitute (Comstock, 1932).
The fact that Philotiella is capable of utilizing members of four polygonaceous
genera, Chorizanthe, Mucronea, Eriogonum and Oxytheca, might argue for a close
relationship among these plants. T h e genus Olcytheca evolved directly from
Eriogonum subgenus Ganysma (Ertter, 1980), whereas Mucronea is a derivative of
Chorizanthe. As noted above, the annual members of Eriogonum and Chorizanthe
evolved independently from their own perennial stock, and it is unlikely that the
annual members of Chorizanthe evolved from the subgenus Ganysma.
Nonetheless, the rust Uromyces intricatus Cooke in North America attacks
members of Chorizanthe, the subgenus Ganysma and 0. dendroidea Nutt. (Savile,
1966), so that whatever attributes all might share (especially biochemically),
these are no doubt detected and used by Philotiella much as they are by the rust.
Philotiella speciosa is fairly constant throughout its range except for the isolated
subspecies bohartorum from Mariposa Co., California. It is larger, darker, whiter
on the lower surface, and with more reduced spotting than nominate speciosa
(Tilden, 1967). Its suspected food plant, Chorizanthe membranacea (along with
C. spinosa S. Wats.), was recognized as a distinct genus by Goodman (1934) who
called it Eriogonella. T h e distinctness of bohartorum might favour the recognition
of Eriogonella which is distinguished from Chorizanthe by its curved (rather than
straight) embryo. Such a distinction (in part) is used to differentiate between
the perennial subgenera Eucycla and Oligogonum of Eriogonum-a taxonomic
division that is recognized not by subspecies, but by the species of Euphilotes!
Monotypic Philotiella can be distinguished from Euphilotes by the venation of
SEQUENTIAL EVOLUTION OF EC'PHZLOTES O N ERZOGONCrM
71
R, its extremely heavy proleg femur, the large tibia1 process of the prothoracic
legs, and the unique aedeagus (Mattoni, 1977). Otherwise, Philotiella appears to
be closest to Euphilotes of all the Scolitantidini genera, and probably was derived
from the ancestor to the central Asian genus Praephilotes. The male genitalia of
Philotiella has a high number of valvae teeth and cristae obliquae present, in
these respects approaching E. rita. Except for the isolated Philotiella speciosa
bohartorum at Briceburg in Mariposa Co., California, P. speciosa speciosa is
relatively uniform throughout its range (Table 3), occurring primarily in arid
desert habitats. The isolated Sierran subspecies differs from nominate speciosa in
its larger size, reduced macules on the secondaries and much broader black
border in the males.
The evolutionary sequence of Euphilotes rita to enoptes and then to bernardino
and battoides (Shields, 1975), based on comparative morphology of adults, is
partly confirmed by the phylogeny of their food plants. Euphilotes rita occurs on
the less advanced sections of Eucycla, whereas E. enoptes and E. bernardino are on
the more advanced ones, and finally E. battoides is found on species of
Oligogonum (Table 6). T h e four species of Euphilotes are primarily mutually
exclusive in their choice of food plants. This suggests that the main development
occurred on Eucycla (greatest number of species utilized), with a radiation of
battoides on Oligogonum. Most food plants of Euphilotes are perennials belonging
to Eucycla and Oligogonum. Euphilotes rita larvae use some of the large, shrubby
(and phylogenetically less advanced) species of Eucycla as their food plants
(Table 6) supporting the concept that E. rita is the most primitive species of the
genus.
Instances of one Euphilotes species giving rise to another always occur when
the pairs occur allopatrically on the same Eriogonum host. These pairs are E. rita
rita and E. enoptes dammersi on E. wrightii var. wrightii, E. enoptes smithi and
E. bernardino allyni on E. parvifolium, and E. enoptes ancilla and E. battoides glaucon
on E. umbellatum var. nevadense. These are almost the only instances known where
two different species of Euphilotes utilize the same host plant species. Such a
coincidence being due to chance alone is highly unlikely.
Euphilotes rita rita probably gave rise to E. enoptes dammersi (Comstock &
Henne). Today, both occur on E. wrightii, near Prescott and at Yarnell,
Arizona. While differing genitalically in valve shape and teeth number,
phenotypically they are similar in the colour of blue and aurora width, and
extremely so in facies (Shields, 197710). With a reduction in valvae teeth number
and loss of the cristae obliquae in the male genitalia of E. enoptes dammersi,
perhaps E. enoptes became genetically isolated from E. rita which allowed
E. enoptes subspecies to evolve on the more advanced species of Eucycla.
Euphilotes enoptes first overlaps the food plant choices of E. rita with E. wrightii
(Table 6 ) in the same section of Eriogonum (Racemosa) that harbours the
satellite E. enoptes spaldingi (Barnes & McD.). The section Racemosa is
phylogenetically the first section of Eucycla that E. enoptes feeds upon.
Euphilotes enoptes ancilla appears to have arisen from spaldingi.
Euphilotes enoptes smithi and E. bernardino allyni are probably closely related
although no hybrids are yet known. Both show fairly strong phenotypic
resemblance although they differ in genitalia. Presumably there were two
different lines from enoptes into 'battoides', one going from enoptes ancilla to battoides
glaucon and the Oligogonum-feeding subspecies, and a second going from enoptes
72
0. SHIELDS AND J. L. REVEAL
smithi to bernardino allyni and the Eucycla-feeding subspecies. Thus, the ‘battoides’
type of bifurcate male genitalia likely evolved twice from fairly closely related
enoptes subspecies, but as two different expressions, with that of the battoides line
being generally larger than that of the bernardino line. Euphilotes enoptes smithi and
E. battoides allyni occur allopatrically on Eriogonum parvifolium in the late summer.
Euphilotes enoptes ancilla probably gave rise to E. battoides glaucon.
Phenotypically the two differ only slightly, although their genitalia are
distinctive from each other. Based on male genitalia, two hybrids are known
from near Jarbidge in Elko Co., Nevada, and from Pattee Canyon in Missoula
Co., Montana (Shields, 1977a). Otherwise, the two subspecies are primarily
allopatric in distribution (Table 7). Presumably the bifurcation of the male
valvae in E. battoides compared with a more spatulate one in E. enoptes afforded
a degree of genetic isolation.
Other species pairs of Euphilotes that allopatrically use the same Eriogonum--i.e. E. enoptes nr. ancilla and E. battoides baueri (Shields) on E. ovalifolium, are
readily distinguishable in facies and have not given rise to one another. These
are examples of competitive displacement (see De Bach & Sundby, 1963;
De Bach, 1966). Of particular interest is the sympatrical use of two different
species of Eriogonum allochronically. Two subspecies of E. battoides, one as yet
unnamed, occur on E. ovalifolium and E. corymbosum near Fredonia, Arizona,
while on E. fasciculatum, E. microthecum and E. heermannii in the Providence
TABLE
7 . Transitional species pairs of Euphilotes
Name
Distribution
1. Euphilotes rita rita (on Eriogonum rurightii var.
wrightii mainly, also on E. polycladon)
Central and south-eastern Arizona in Cochise,
Maricopa and Yavapai Cos., eastward to Dona
Ana, Catron, Hidalgo and Grant Cos. in southwestern New Mexico and Brewster Co., Texas
Euphdotes enoptes dammersi (on Eriogonum wrightii var
wrightii mainly, also on E wrightii var.
membranaceum and E. elongatum var. elongatum)
Southern California from eastern San Diego, eastern
Orange and north-western Riverside Cos. north
to north-eastern San Bernardino Co. east to Clark
and Lincoln Cos., Nevada, and Mohave, Yavapai
and western Gila Cos., Arizona
2. Euphilotes enoptes smithi (on Eriogonum parvijolium
var. paruijolium and E. latijolium)
Euphilotes bernardino allyni (on Eriogonum parvzjolium
var. paruijolium)
Coastal Monterey and Santa Cruz Cos., California
3. Euphilotes enoptes ancilla (on Eriogonum umbellatum
mainly, also on E. heracleoides, E. lobbii,
E. oualijolium and E. strictum)
Western and northern Nevada north to Harney Go.,
Oregon and south-western Idaho, eastward across
northern Utah to western Colorado, extreme
western Wyoming and south-western Montana.
Also Cypress Hills, Alberta, and Val Marie and
Rosefield, Saskatchewan, Canada
Euphilotes battoides glaucon (on Erigonum umbellatum
and E. heracleoides mainly, also on
E. sphaerocephalum and E. flavum var. piperi)
Eastern and north-eastern California and extreme
western Nevada through central and northeastern Oregon to central Washington, extreme
southern British Columbia and south-western
Idaho; isolated segregates in Montrose Co.,
Colorado, and south-eastern Coconino Co.,
Arizona
Coastal Los Angeles Co., California
SEQUENTIAL EVOLUTION OF EUPHILO TES ON ERIOGONUM
73
Mountains, California are E. bernardino (on E. fasciculatum) and E. bernardino
‘Eastern Mojave’ (on the other two, preferring E. microthecum). Euphilotes battoides
battoides and E. battoides intermedia are sympatric at Mammoth, Mono Co.,
California. Also, E. rita emmeli (Shields) on E. leptocladon and E. battoides ellisii
(Shields) on E. co7ymbosum fly together near Church Rock, Arizona, without
switching to each other’s host plants (see Table 6 ) . At Old Woman Mountains
in San Bernardino Co., California, E. enoptes mojaue and E. bernardino martini are
sympatric but occupy different microhabitats, with mojaue preferring wash
bottoms and with martini occupying benches.
The primary radiation of Euphilotes has occurred on perennial Eriogonum
species and secondarily on a few annuals. Euphilotes enoptes mojaue (Watson &
W. P. Comstock) is widespread on E. pusillum Torr. & Gray in the Mojave
Desert, but all other annual-feeders seem to have limited distributions. Euphilotes
rita rita which feeds mainly on perennial shrubs of the subgenus Eucycla has
been observed on two annuals, E. polycladon Benth. in DC. and E. rotundzfolium
Benth. in DC. Similarly, E. enoptes tildeni (Langston) which normally feeds on
E. nudum Dougl. ex Benth. has been found on the annual E. couilleanum Eastw.
Even so, E. enoptes mojaue may be seen on an occasional perennial species
(E. nudum). All of these instances seem to be an example of opportunistic
feeding.
Occurrences of opportunistic feeding by Euphilotes are randomly scattered
among extant species. The case of E. enoptes mojaue is exemplary. Population
densities of Eriogonum pusillum are nearly always high, but in poor years, or in
areas of local stress, numbers can be significantly reduced. At such times,
E. enoptes mojaue may have switched from the annual E. pusillum to the perennial
E. nudum (or vice versa). I n doing so, a few populations of mojaue are able to
survive and reproduce on E. nudum at the north-western margin of its range.
Euphilotes enoptes tildeni, on the other hand, has been found to switch from
E. nudum to E. covilleanum for just the opposite reasons. I t uses the annual
E. couilleanum in May only in favourable years, while it uses E. nudum more
abundantly and during most years from July to September. T h e two flights are
nearly indistinguishable in appearance. A similar situation is encountered in
E. rita rita when it is found on the annuals E. polycladon and E. rotundzfolium. This
is not unique to Euphilotes, and not unlike that observed in 1966, during a
population explosion involving two California desert Papilio L. I n this case,
P. indra fordi Comstock & Martin and P. rudkini Comstock began using each
other’s normal host plants after defoliation of their own (Emmel & Emmel,
1969).
PHYLOGENETIC DEDUCTIONS
Eucycla is the largest and most complex subgenus of Eriogonum and has
sections that have differences often as great as or greater than differences
between the other subgenera (Reveal, 1969b). Reveal noted that there are
species in Ganysma, that had evolved from Eucycla, that link it with
Oregonium. Euphilotes rita and E. enoptes radiated on Eucycla and are also found
on annual species of Ganysma and Oregonium, while E. battoides, which
radiated on Oligogonum, is not found on these annual subgenera.
Hovanitz & Chang (1965) and Hovanitz (1969) have shown that Pieris rapae
74
0 SHIELDS AND J L. REVEAL
L. larvae can be induced to prefer an alternate host in the laboratory, with the
resulting adults preferring that plant for oviposition. Perhaps E. battoides and
E. bernardzno out-competed both enoptes and rita, since they are usually more
numerous than either. Eriogonum corymbosum usually grows in large colonies, and
there is some evidence for this competitive displacement. For example,
E. battoides and E. bernardino are predominant on varieties of E. heermannii and
E. corymbosum respectively although rita uses these in at least one locality for each
where battoides apparently does not occur. Also, both enoptes and battoides are
allopatric on E . parvzfolium and E. umbellaturn.
Major differentiations of species in Eriogonum have occurred from Middle
Pliocene to the Present in association with the spread of deserts in south-western
North America (see Axelrod, 1950). Prolonged pupal diapause correlated with
an irregular blooming time for desert larval hosts (see Nakamura & Ae, 1977;
Sims, 1983) probably occurs in Euphilotes and Eriogonum. As a n arid climate is
thought to be a stimulus for rapid plant evolution (Axelrod, 1967, 1972;
Stebbins, 1952; Reveal, 1980; Raven & Axelrod, 1978; Axelrod & Raven,
1985), the evolution of Eziphilotes should follow that of Eriogonum in time
= sequential evolution). Indeed Eriogonum is the largest endemic North
American genus of flowering plants, and Euphilotes is the most variable lycaenid
genus in North America. Euphilotes populations were probably once more
continuously connected, perhaps in moister times to account for their presentday discontinuous distributions, often in isolated colonies and sometimes
disjunct.
Neoteny (the prolonging of the juvenile stage into the mature stage in
ontogeny) can be induced by stressful environmental conditions such as occur in
harsh deserts. The step from perennial to annual in Eriogonum by neoteny would
have involved a n abrupt and radical simplification of the phenotype and its
despecialization (Takhtajan, 1976). Increased evolutionary plasticity by
neoteny would open new evolutionary pathways for rapid adaptive radiation
(Grant, 1977). This could account for the evolutionary ‘explosion’ exhibited by
Eriogonum (see Colbert, 1953; Romer, 1960).
Neogene floras indicate a warm, semiarid climate for Late Miocene time in
the western United States (Axelrod, 1948). Rapid evolution of angiosperm
species took place during that time. T h e Late Miocene was the warmest, driest
stage of the Miocene in southern California, with a desert-border aspect to
woodland and chaparral communities in interior southern California (Raven &
Axelrod, 1978). The present desert vegetation there and to the east in the
Intermountain West is no older than the Late Miocene (Axelrod, 1950; Axelrod
& Raven, 1985).
The last major faunal exchanges across the Bering land bridge took place in
Late Miocene time (Hopkins, 1959). The exchange direction for mammals at
least during Pliocene and Pleistocene times was mainly from eastern Asia to
North America (Repenning, 1967; table 9). A seaway covered the land bridge
again about 3.5 m.y. BP. The Praephilotes ancestor to Philotiella probably crossed
the Bering land bridge 3.5-4.0 m.y. BP, during the Early Pliocene.
Unfortunately Pliocene fossil floras are poorly known in Alaska and are
exceedingly depauperate compared with those from Miocene time (Wolfe, 1969,
1972).
il Pliocene Praephilotes-Philotiella link was most likely from a Bering land
f
SEQUENTIAL EVOLUTION OF EUPHILOTES O N ERIOGOXUM
75
bridge rather than a North Atlantic (Thulean) land bridge connection, since
fossil mammals indicate the Thulean land bridge existed only until Middle
Eocene times, c. 49 m.y. BP (McKenna, 1972a, b, 1975).
The time of origin of the Praephilotes, Paleophilotes and Micropsyche complex in
central Asia theoretically should coincide with the Pliocene (or perhaps Late
Miocene) Nearctic development of Philotiella and Euphilotes. T h e Alai Mountains
insect fauna endemic elements arose largely during the Late Miocene (Mani,
1968). The most intense diastropic activity took place during Early Miocene in
the Himalayas, the final phase commencing in the Pleistocene (Athavale, 1973).
It was not until the mid-Miocene phase of the Himalayan orogeny that an
alpine insect fauna developed there (Mani, 1962). In Afghanistan, most of the
alpine morphological features are Mio-Pliocene (Boulin, 1981). The Tyan Shan
underwent block faulting and tilting in the mid-Miocene (Holmes, 1965), while
the Issyk Kul depression and the extremely seismic Tyan Shan and Nan Shan
indicate that they lie along a n old plate boundary (Crawford, 1974;
Anonymous, 1977), where Paleophilotes also occurs.
If the Zizeerini and Scolitantidini are in fact closely related, then the earliest
Scolitantidini (Paleophilotes, Praephilotes, Micropsyche, Philotiella, Euphilotes) in the
Late Miocene were derived from the Zizeerini, a highly successful tribe with a
Gondwanaland and Angaran-Cathaysian distribution and ancient Late
Cretaceous origin. T o date, however, fossil Lycaenidae are known only as far
back as the early Tertiary (Whalley, 1986).
Chromosome numbers of Euphilotes are variable: rita emmeli, n = 33 (Grand
Co., Utah); ritapallescens (Tilden & Downey), n = 25 (Nye Co., Nevada; Mono
Co., California) and n = 34 (Churchill Co., Nevada; Tooele Co., Utah); enoptes
dammersi, n = 23 or 24 (San Bernardino Co., California) and n = 28 (Riverside
Co., California); and battoides ellisii, n = 24 (Kane Co., Utah) (T. C. Emmel &
0. Shields, unpublished). The modal haploid chromosome number for
Lycaenidae is x = 24, and somewhat distantly related genera to Euphilotes
(Pseudophilotes, Turanana, Scolitantides Hubner, Glaucopsyche Scudder) have x = 23
or 24 (Shields, 1975). The deviation of Euphilotes from the base x = 24 may be
due to the stressful desert environment (see also Nevo, 1969) and may mean that
some of the subspecies or even populations of subspecies are genetically
incompatible and are full species instead. Similarly, the Megathymidae, another
group restricted to xeric habitats, are highly host-specific and variable in their
chromosome numbers (Freeman, 1969). Clearly, chromosome fragmentation in
environments with high stress can increase genetic flexibility (Emmel, Trew &
Shields, 1973). A broad survey of the various Euphilotes subspecies for
chromosome counts might prove to be rewarding. Known chromosome counts
for Scolitantidini and relatives (various sources, especially Robinson, 197 1) are
given in Table 8.
Without doubt the radiation of present-day subspecies of Euphilotes on
Eriogonum occurred after Eriogonum was well established. The repeated glacial
episodes in North America during the Pleistocene (Flint, 1971) must have acted
as a great ‘speciation pump’ then much as it has during and following the
Wisconsin glacial event. Such a pump would have been equally significant on
both, but with the effects of a different intensity for each. Considering only the
modern species of both genera, we now wish to propose a series of working
hypotheses that accept the notion that the relationship between the two is one of
0. SHIELDS AND J. L. REVEAL
76
TABLE
8. Chromosomal numbers of Zizeerini and Scolitantidini
Name
Zizeerini
<izula hylax F.
Zizeerza maha (Kollar)
Scolitantidini
Turanana panagaea H.-S.
Philotes sonorensis F. & F.
Pseudophiiota uicrama Mr.
Pseudophilotes baton Bergstr.
Sinia bauius Ev.
Srolitantides orion Pal.
Glaucopsyche alexis Poda
Glaucopsyche melanops Bdv.
.Waculinea alcon D. 8~ Schiff.
Maculinea arion (L.)
.!daculinea nausithous (Brg.)
lolana iolas Ochs.
Locality
Counts
(n)
Uganda
Japan
24
24
Turkey
California
Yugoslavia
Italy
Turkey
Podsused
Austria, Turkey
Htes-Alpes
Italy
Stenjevec
Ai n
Turkey
24
17-44
24
24
24
23
23
23
23
23
24
22
‘sequential evolution’ (Jermy, 1976), and that the speciation processes resulting
in the series of subspecies in Euphilotes involved both the concept of ‘host plants
as islands’ and ‘host switching’.
The majority of subspecies of Euphilotes are primarily found on a single species
of Eriogonum, and some only on a single variety. Such high specificity as seen
currently must have been the case at least for some ancestral subspecies of
Euphilotes in the past. Nonetheless, it seems reasonable to assume that at the
species level, as is the case today, the various butterfly subspecies ought to occur
on several different kinds of wild buckwheat. Differentiation at the subspecific
level ought to have been associated with either switches from one closely related
kind of Eriogonum to another in association with a geographical disruption of the
range, or switches to an unrelated wild buckwheat within a restricted
geographic range.
Next, if the modern sibling species complex in Euphilotes is properly arranged,
that is, E. rita gave rise to E. enoptes, and it in turn gave rise to E. bernardino and
E. battoides, then one ought to find a common point of association either with a
single species of Eriogonum or with a group of related species if that
differentiation at the species level is relatively recent. Likewise, one should
expect to see a relatively restricted range of host species in the primitive
butterfly species with a much greater range in the more advanced ones.
Finally, if there is a competition factor associated with subspeciation, one
would expect those of the more advanced species of butterflies able to dominate
the subspecies of both lesser advanced species or even subspecies.
In looking at wild buckwheat plants as individual islands (Janzen, 1968,
1973) in relation to taxa of Euphilotes that use them, clearly there are factors that
determine primary utilization.
The modern species of Euphilotes tend to use subshrubby or shrubby species
that produce, at any given moment, numerous flowers arranged in close
association with one another. A given involucre of Eriogonum can produce
several hundred flowers over the growing season. I n some perennial species
flowers may be present year-round (as in E. fasciculatuni or E. parvijlorum), but
SEQUENTIAL EVOLUTION OF EUPHILO TES ON ERIOGONUM
77
even in those that are seasonal, once flower production begins, a given involucre
may produce flowers for several weeks or months (as in E. nummulare). I n most
perennials, numerous involucres are produced a t a single node, and like the
flowers they produce, these involucres are also maturing throughout the
growing season so that flowers of various ages can be in a single cluster. As the
flowers mature and the fruits develop, the tepals (modified sterile segments that
resemble petals) remain so that old tepals can be found on the plant even after
the fruit has fallen away. I n addition, pollen and nectar can be produced over
an extended period of time as well, and in some species of Eriogonurn, the amount
of nectar can be copious (e.g. E. fasciculatum).
The arrangement of clusters of involucres into inflorescences must be a factor
in this story. Many perennial species of Eriogonurn have inflorescences consisting
of involucres arranged in compact heads, cymes or umbels. This is true, for
example, in E. coryrnbosurn, E. fasciculatum, E. ovalifolium and E. umbellaturn to
mention only a few. Racemose inflorescences are found in such species as
E. racernosum, E. leptocladon and some expressions of E. nurnmulare, whereas the
inflorescences of E. efusurn are more or less intermediate between a cyme and a
raceme. In the racemose species, there is not only a sequenced maturation of
flowers and involucres a t a given node, there is a similar sequence along the
inflorescence itself. Even species that produce umbels and cymes will have a
maturation sequence both within a given inflorescence and in different
inflorescences on the same plant.
T h e size of the inflorescence is partially associated with the size of the flower.
Some of the largest flowers are found in species of the subgenus Oligogonum
such as Eriogonurn urnbellaturn, E. heracleoides and E. cornpositurn, plants that have
not only large, open umbellate inflorescences but bright yellow flowers as well.
I n fact, the yellower the flower, the smaller it is in some species of this subgenus.
I n those species that produce tight heads, such as E. ovalzfoliurn, those with
yellow flowers tend to be smaller than those with white flowers (compare the
var. ovalzfolium with var. nevadense Gandoger, for example). Perhaps the bright
colour display in some way compensates for the reduced inflorescence.
Nonetheless, all have relatively large flowers compared with other species in the
genus.
T h e low, cespitose perennial species of Eriogonum with very small flowers,
interestingly, are not used by Euphilotes. While Euphilotes are known to occur on
E. marifolium and E. incanurn in the Sierra Nevada, the butterfly is not found on
E. rosense or the alpine E. ovalifoliurn var. nivale (Canby in Cov.) M. E. Jones
which occur sympatrically. At lower elevation, where Euphilotes is found on
varieties of E. microthecum and E. urnbellaturn, it has not been found on
E. caespitosum. I n this latter case, however, E. caespitosum often flowers before
either E. microthecum and E. urnbellaturn, and this may be more significant than
flower size. Near Westgard Pass, Inyo Co., California, E. battoides baueri uses
E. ovalzfoliurn var. ovalifoliurn that grows mixed with a more abundant
E. caespitosurn that is not used (Shields, 1975).
An important factor seems to be the relative size of the wild buckwheat plant
compared with those of other species in the local habitat. I n areas where tall
shrubs dominate, Euphilotes tends to prefer the shrubby species of Eriogonum, but
when the shrubs are low (as in some desert or high elevation areas), the
butterflies will be seen in association with perennial herbs or low subshrubs.
78
0. SHIELDS AND J. L. REVEAL
Eriogonum oualfolium is a highly variable species, having a long inflorescencebearing stem at low elevation and a shorter one when the plant forms compact
mats at high elevations. Euphilotes are found on each extreme. Euphilotes en0fte.r
ancilla and E. battoides baueri use E. oualzfolium var. ovalzfolium and var. nevadensp
Gandoger in low elevation, desert habitats where the stems are tall and the
flowers may be either white or yellow, while E. battoides glaucon is on
E. oualzfolium var. niuale in the high mountains of the Pacific Northwest. Even
when a low, matted perennial is used at a low elevation, it is often both locally
common, forming large mats or producing numerous individuals, and in a
habitat where the larger plants are widely dispersed and infrequent in number.
This is the case with an unusual form of E. bernardino that occurs on a n equally
unusual form of E. shockleyi var. shockleyi in east-central Nevada and E . enoptes
langstoni on E . kennedyi var. purpusii (Brandegee) Reveal in Munz.
Some of the most interesting comparisons involved annual versus perennial
species of Eriogonum. Eriogonum trichopes Torr. and E. cernuum Nutt. are both
widespread and variable annuals, yet Euphilotes is not on them (one record of use
of E. cernuum is known). These species are glabrous and have cymose
inflorescences that produce downwardly pointing solitary involucres. While
individual plants of these species may be in flower for long periods of timc
( E . d@eeXum Torr. in Ives will flower year-round), the distance from involucre to
involucre (ignoring its position on the branch) can be considerable. Yet, thc
perennial shrub E. heermannii is also glabrous and with equally widely spaced,
solitary involucres. I n the perennial, however, the involucres are arranged
vertically on the branch. Numerous annual species in the subgenus Oregonium
have sequentially maturing, solitary involucres upwardly arranged along
pubescent branches, yet none is used by Euphilotes to a significant degree. Yet,
the perennial E. plumatella, with similarly sparse inflorescences, is used. Herc,
there may be a key. There is both a pubescent and glabrous expression of
E. plumatella; so far Euphilotes has been found to prefer the pubescent phase. In
the one limited example of use in the subgenus Oregonium, both the glabrous
E. baileyi var. baileyi and the pubescent E. baileyi var. praebens (Gandogerj
Reveal-formerly
called var. diuaricatum (Gandoger) Reveal-are
used by
E. rita pallescens on those rare occasions when it is not on E. nummulare in westcentral Nevada.
Another factor that must be important in the concept of the host plant as an
island, is the distribution-or
size-of
that island. While to the individual
butterfly it is significant to examine the size of a single plant in relation to other
insects on it (Janzen, 1973), the overall availability of individual islands and the
diversity of the habitat those islands occupy is critical to the evolution of the
taxon as a whole. To quote Opler (1974):
. . . we might hypothesize that a plant host of increasingly large distribution
will expand into a larger and larger range of ecological habitats. This
allows for ( I ) an increasing probability that insect populations requiring
specialized habitats will survive, while reducing the probability of
extinction due to interspecific competition or extremes of the physical
environment; and (2) a n increasing probability of successful colonization by
insects new to that host.
It is significant to note that no subspecies of Euphilotes is currently restricted t o a
SEQUENTIAL EVOLUTION OF EUPHILOTES O N ERIOGONUM
79
narrowly endemic species of Eriogonurn although E. enoptes langstoni which is
known only on E. kennedyi var. purpusii comes close. The fact is that most
Euphilotes occur on plants of widespread distribution that form locally dense
populations of, in many cases, nearly pure stands. For Euphilotes, this is true of
such important Eriogonurn species as E. microthecum, E. fasciculatum, E. corymbosurn,
E. leptocladon, E. efusurn, E. heermannii, E. wrighti, E. nudurn, E. oualfoliurn,
E. umbellatum, E. cornpositum and E.Jauum. Also, each of these plant species is
divided into several (in the case of E. urnbellatum, over 30!) morphological and
geographically distinct varieties found over a wide range of habitats. Varieties of
E. wrightii, just to cite one example, occur from sea level in Baja California to
over 12 000 feet elevation in the Sierra Nevada, and the species ranges from San
Luis Potosi, Mexico north to the north rim of the Grand Canyon in Arizona,
and from central Baja California north to northern California in the Coast
Ranges. Further, E. racernosurn, used exclusively by E. enoptes spaldingi, is highly
variable although it is not divided into finer taxonomic units (Reveal, 1978,
1981). Still, Euphilotes has not been found on such widespread species as
E. lonchophyllum Torr. & Gray of the subgenus Eucycla, E. annuum Nutt. of
subgenus Micrantha, E. hieraczfoliurn of subgenus Pterogonum, E. inJatum Torr.
& Frkm. and E. abertinum Torr. in Emory of subgenus Ganysma, and
E. uimineum Dougl. ex Benth. of subgenus Oregonium.
Certainly, with such a variable and widespread series of Eriogonum as host
plants, would one not expect to find an equally diverse array of Euphilotes
subspecies on them?
Even when considering only those species of Eriogonurn that are infrequently
used by Euphilotes, few are rare and local. Euphilotes enoptes ancilla has been
observed on E. lobbii var. robustius (Greene) M. E. Jones in west-central Nevada
and E. battoides battoides is infrequently on E. polypodurn, a narrowly restricted,
high elevation species in the southern Sierra Nevada, but most of these
secondary hosts fall into a different category. Eriogonurn batemanii, for example, is
used sparingly by E. battoides ellisii. This plant is locally common on clayey hills
in eastern Utah, but it is clearly not the preferred host and appears to be used
only when E. coryrnbosurn is not immediately available locally. A similar
observation might be made for E. saxatile S. Wats. which is used by E. enoptes
enoptes or E. wrightii var. membranaceum Stokes ex Jepson used by E. enoptes
darnrnersi (except in eastern San Diego Co., California, where it is extensively used).
From these observations, a picture emerges that suggests that Euphilotes prefers
individual wild buckwheat plants that are obvious in the local habitat, that
have numerous flowers in an easily accessible arrangement available over an
extended period of time, and that tend to be found in a variety of habitats.
Euphilotes also has tended to gravitate toward species of Eriogonum that are
widely distributed but a t the same time are highly variable so as to be composed
of a series of distinct morphological and geographic varieties. The islands
required for the successful establishment of infraspecific diversity within
Euphilotes have been met by the equally successful infraspecific diversity within
Eriogonum associated with its edaphic and microhabitat islands.
The concept of host switching in association with subspeciation in Euphilotes is
significant. From the data in Table 6, Euphilotes rita first extensively radiated on
species of section Corymbosa, one of the most primitive sections in the subgenus
Eucycla. Euphilotes enoptes, on the other hand, radiated on a single group of
80
0. SHIELDS AND J. L. REVEAL
species belonging to the more advanced sections of Eucycla, while E. battoides
and E. bernardino developed on two different groups of species, the former on
species of the subgenus Oligogonum and the later on the more primitive
members of Eucycla.
All Euphilotes with valve teeth (rita and enoptes) can be grouped into two
phenotypic assemblages of subspecies. I n E. rita, the pallescens group (mattonii,
pallescens and elvirae) has low teeth numbers (15-19), while the rita group
(emmeli, coloradensis and rita) has higher numbers (20-26). I n E. enoptes, the
spaldingi group (dammersi, mojaue, spaldingi, ancilla and columbiae) has low teeth
numbers ( 13-15), whereas the enoptes group (langstoni, enoptes, tildeni, smithi and
bayensis) has higher numbers (16-21). I n E. bernardino and E. battoides the teeth
are not present on the valve, but they too can be grouped into two phenotypic
assemblages of subspecies. I n E. bernardino these are the bernardino group (allyni,
bernardino and martini) and the ellisii group (ellisii and ‘Eastern Mojave’). In
E. battoides these are the battoides group (glaucon, baueri and battoides) and the
intermedia group (intermedia, comstocki, oregonensis and centralis). In all four sibling
species of Euphilotes, comparatively speaking, the first group is associated with
the less advanced species of Eriogonum while the second group is associated with
the more advanced species of Eriogonum.
T h e least specialized and uniform subspecies of Euphilotes rita is rnnttonii. It is
known to occur only on Eriogonum microthecum var. LaxiJlorum, a widespread
variety that today occurs from eastern Washington, northern Idaho and western
Montana south through the Intermountain Region to eastern California,
southern Nevada, northern Arizona and western Colorado (Reveal, 197 1 ) . Yet,
E. rita mattonii is known only from the sagebrush, volcanic foothills of the
Jarbidge Mountains of northern Elk0 Co., Nevada, between Highway 43 and
Charleston Reservoir. This mountain range was subjected to limited glaciation
at its higher elevations, but the surrounding lower elevations were not
inundated by pluvial lakes thereby probably providing a haven for the var.
laxzjorum to survive during late Pleistocene time. I t is thought that as the
Pleistocene ended, and the resident low elevation flora moved elevationally
upslope, mattonii probably followed var. laxzjorum into the higher mountains. In
this fashion, the Jarbidge Mountains became a continental island (Brown, 1978)
and rnattonii was prevented from moving beyond the confines of this island due
not only to the lack of its host but also because of the distances to the next
available montane site where the var. 1axzJorum is found were too great.
Euphilotes rita mattonii appears to form a link between Philotiella speciosa and the
other subspecies of rita. The subspecies mattonii occupies a rather isolated
position within rita but would appear to be most closest related to E. rita
pnllescens. Recently a population morphologically near mattonii was found in close
association with E. deJ?exum a t Rest Spring, at about 6400 feet elevation in the
Cottonwood Mountains, Inyo Co., California. No E. microthecum was found
nearby although the var. simpsonii is known from the area. Here E. dejlexum is a
dominant, abundant plant a t this locality.
If mattonii is the point of origin for Euphilotes rita pallescens as suggested in
Fig. 2, then its development must have occurred at a time prior to mattonii
becoming restricted in its distribution. Such a scenario is possible if mattonii was
once much more widespread in its distribution. At such a time, one would
expect a host switch event to occur, with the butterfly moving from
SEQUENTIAL EVOLUTION OF EUPHILO TES ON ERIOGONUM
81
E. microthecum to E. nummulare, the primary host of pallescens. Areas of presentday overlap between E. nummulare-a plant of sandy soils mainly in the valley
bottoms and along the lower foothills of desert ranges from eastern California
across Nevada to southern Utah south to north-western Arizona-and
E . microthecum are rare. However, in the southern part of the range of
E. nummulare, E. microthecum var. laxijlorum gives way to E. microthecum var.
simpsonii, and these two d o occur sympatrically. Today, pallescens may be found
on var. simpsonii so that it is possible the switch of hosts that resulted in the
differentiation ofpallescens involved an intermediate step via var. simpsonii. If this
were the case, mattonii would have remained restricted to var. laxiflorum and
confined to its range. Perhaps it is not merely coincidence that today mattonii
occurs in the precise centre of the range of E. microthecum var. laxijorum (see
Reveal, 1971: fig. 6).
Indirect evidence for this is seen in the evolution of Euphilotes rita emmeli on
Eriogonum leptocladon and E. rita coloradensis on E. efusum which shall be discussed
shortly.
Eriogonum nummulare occurs today mainly on moving sands a t or below the
level of the pluvial Lake Lahontan and Lake Bonneville. Such sites are widely
scattered, and while the population densities in any given location may be
exceedingly high (in some cases E. nummulare is the dominant shrub), these sites
are highly fragmented and widely dispersed. It is thought that during the
Wisconsin Ice Age, E. nummulare probably occurred OD,sandy soils near the lake
shores, and that such sites were rather continuous. With the drying of the lakes,
and the desertification of the valley bottoms resulting in the formation of sand
dunes, these populations were disrupted. It seems clear that Euphilotes rita
pallescens was probably widespread during the past, as today it occupies
essentially the same range as its host (Table 1). However, as a result of the
fragmentation of E. nummulare into isolated populations, so too has pallescens
fragmented into isolate, more or less distinct populations.
Euphilotes rita pallescens is rather variable. I n the eastern part of its range, from
north-eastern Nye Co. eastward to Tooele Co., Utah, however, the populations
are fairly uniform. This may be accounted for by the continued survival of
Eriogonum nummulare in this area even during Late Pleistocene time. Populations
of the plant today tend to occur on the beach sands associated with Lake
Bonneville, and it is conceivable both the plant and the butterflies occupied this
area in the past. In the western part of its range, pallescens is quite variable not
only in its expressions but in its host plants as well. Along the Lahontan Trough
called
(Reveal, 1980), a southern expression of E. nummulare-formerly
E . kearneyi var. monoense (S. Stokes) Reveal-occurs
intermixed and mostly
indistinguishable from typical E. nummulare. Here, isolated populations of
pallescens have developed on E. nummulare differing in only minor features from
one another. Near Little Washoe Lake in Washoe Co., Nevada, a population of
pallescens is found on E. baileyi; it differs from the typical expression in being
smaller and having a series of minor morphological modifications. At Pyramid
Lake, pallescens is on E. heermannii var. humilius ( S . Stokes) Reveal in Munz but in
this case the differences are less than those found in the butterflies on E. baileyi.
Clearly, Euphilotes rita pallescens appears to be in the process of differentiating a
new subspecies associated with a fundamental host switch. The change to the
annual Eriogonum baileyi, with its more northern range, may provide an avenue
82
0. SHIELDS AND J. L. REVEAL
for northward migration, isolation, and successful subspeciation of what is now a
minor variant.
The present-day range of Eriogonum nummulare, the host of Euphilotes rila
pallPscens, and E. plumatella, the host of E. rita elvirae which is thought to have
evolved from pallescens, do not overlap with the possible exception of some areas
in extreme southwestern Utah and adjacent portions of Arizona and Nevada.
Eriogonum plumatella occurs from this portion of Utah south into Mohave Co.,
Arizona, then west across southern Nevada to southeastern California. Like
fi. nummulare, E. plumatella is a species of generally sandy soils, but it occurs on
the warm Mojave Desert rather than in the colder Great Basin. The present-day
distribution of E. plumatella is highly fragmented with widely scattered, local
populations. Only rarely is the plant the dominant expression in a given habitat.
Nonetheless, even with the southward extension of the ranges of Eriogonum
nummulare, it is difficult to account for its coming in contact with E. plumatella.
Certainly, the host switch event involving the evolution of elvirae from pallescens
must have been recent and the zone of potential overlap restricted. Likewise, the
period of time when the two Eriogonum species occupied overlapping (or nearly
so) ranges must have been short so that the resulting isolation of the butterflies
produce little in the way of marked morphological differentiation as would be
predicted according to the Wallace Effect (Grant, 1966, 1981).
The populations of Euphilotes rita elvirae that occur on Eriogonum plumatella are
relatively uniform throughout their range in the western portion of the Mojave
Desert. However, there appears to be some gene flow between pallescens and
elvirae based on undersurface characters (Shields, 1977a). Populations of the two
subspecies intermix in Kern, Inyo and Mono Cos., California, and Mineral Co.,
Nevada, with some intergrades occurring between the two. Here the primary
host plants are E. nummulare and E. microthecum var. ambiguum (M. E. Jones)
Reveal in Munz, with elvirae using mainly the var. ambiguum. Both E. ritn
subspecks are similar in teeth number averages of the valvae. At Butterbread
Peak in Kern Co., California, elvirae uses E. davidsonii in mid May, and later in
the year, used E. plumatella and E. microthecum. Not far from there at Skyline
Ranch, larvae have been found on E. wrightii var. subscaposum and E. roseum
Dur. & Hilg.
'I'he close relationship among Eriogonum microthecum, E. efusum, E. corymbosum,
E. leptocladon and E. nummulare has long been recognized. Reveal (1968) treated
the E . corymbosum complex in detail, noting there and elsewhere (Reveal, 1971)
that there was a series of seemingly transitional populations across extreme
southern Utah, northern Arizona and northwestern New Mexico involving
(west to east) E. nummulare, E. leptocladon var. ramosissimum (Eastw.) Reveal and
E. efusum var. efusum. The evolution of Euphilotes rita emmeli on E. leptocladon
from E. rita pallescens on E. nummulare, and then from emmeli to E. rita coloradensis
on E. effusum var. efusum seems to follow exactly the same developmental
pathway. In pure stands of each host species, the three subspecies of E. rita are
distinct.
Euphilotes rita emmeli occurs on Eriogonum leptocladon var. leptocladon in eastern
Utah, on var. papiliunculi Reveal in southcentral Utah, and on var. ramosissimum
throughout its range in southern Utah and northern Arizona and on
E. nummulare east of Hurricane, Washington Co., Utah, and at Pipe Spring in
adjacent Coconino Co., Arizona. I n Wupatki National Monument, emmeli also
SEQUENTIAL EVOLUTION OF EUPHILOTES ON ERIOGOHUM
83
uses the annual E. dejlexum var. dejlexum in an area where the perennial
E. leptocladon var. ramosissimum is common. Clinal populations involving the
subspecies emmeli, rita and coloradensis occur in northwestern New Mexico
(Shields, 1975) where intergradation between E. leptocladon var. ramosissimum
and E. effusum var. efusum are known to occur (Reveal, 1971). Another clinal
series, involving emmeli and pallescens, is found in Washington Co. of
southwestern Utah where E. nummulare and E. leptocladon var. ramosissimurn tend
to intergrade. Interestingly, the western clinal phase, in its ultimate expression
which is near pallescens, has undergone a host switch from the perennial
E. nummulare to the annual E. dejlexum var. nevadense Reveal in Washington Co.,
Utah.
The subspecies coloradensis probably gave rise to Euphilotes rita rita. The former
occurs primarily on Eriogonum efusum var. efusum [it was reported once on
E. cernuum (but no voucher specimen was collected) in Arapahoe Co., Colorado,
and has been found in association with E.Javum in Albany Co., Wyoming, a
plant that tends to flower before E. effusum in this area] which is a plant typical
of the western Great Plains from western South Dakota south to New Mexico,
but the latter is on E. wrzghtii var. wrightii. That host plant occurs from central
Mexico to western Texas and then across New Mexico to eastern California.
The two plants overlap today only in west-central New Mexico, but during the
Late Pleistocene, during the formation of the Chihuahuan Desert (Wells, 1977),
it was likely that the range of the two overlapped to a much greater extent in
what is now northern Mexico and southern New Mexico. With the northward
movement of the Great Plains flora into its present-day position, rita expanded
its range. To the north, in central New Mexico, there are a series of clinal
populations involving it and coloradensis, but to the west, unencumbered by
competing subspecies, it flourished.
Except for a transgression onto the annual Eriogonum polycladon in Grant Co.,
New Mexico, Euphilotes rita rita is found only on E. wrightii. As for the clinal
populations between rita and coloradensis, most are found on E. efusum var.
effusum, but populations also were found on E. corymbosum var. velutinum Reveal
and even on the annual E. rotundzfolium Benth. in DC.
Euphilotes enoptes dammersi is considered to be the basic subspecies for this
species (Shields, 1977a) and is thought to have evolved from E. rita rita. Both
species share the same host plant, Eriogonum wrightii var. wrightii, but except for a
narrow range of overlap in central Arizona, the two are not sympatric. What
differences might have existed between the two species early in the
differentiation of enoptes from rita, they were rapidly reinforced by geographical
isolation. Throughout most of its range in the deserts of the Southwest, dammersi
is found only on E. wrightii. I n the mountains of southern California, dammersi
switched over to E. wrightii var. membr~naceum and E. elongatum Benth. var.
elongatum-the latter related to E. wrightii (Reveal, 1969). When enoptes dammersi
has been found on other hosts, there have been no significant morphological
changes in the butterfly except for the slightly smaller size and atypical
condition of those rarely found on the annual E. dauidsonii Greene in the Santa
Rosa and San Jacinto mountains of Riverside Co., California. In the eastern
Mojave Desert it sometimes uses E. plumatella and E. panamintense Morton.
Euphilotes enoptes spaldingi is found essentially throughout the range of its host
plant Eriogonum racemosum Nutt. This plant is closely related to E. wrightii, and it
84
0. SHIELDS AND J. L. REVEAL
seems reasonable to assume that the host switch, coupled with the more
northern range of E. racemosum, permitted the successful subspeciation. Indeed,
the only specimen of spaldingi reported from California is somewhat similar to
E. enoptes dammersi in appearance. One specimen of spaldingi from Swain Creek in
Kane Co., Utah, shows a strong tendency toward E. enoptes ancilla on the upper
and undersides (Shields, 1975). Occasionally, specimens of ancilla from the
Toiyabe Range in central Nevada show a slight tendency toward spaldin'gi
(Shields, 1977a).
The establishment of Euphilotes enoptes enoptes was a major development in the
evolution of the genus, although the switch from Eriogonum wrightii var. wrightii
to varieties of E. nudum is not all that significant in terms of host evolution. Its
distribution in the mountains of California, on var. pauctjlorum S. Wats. in
southern California, var. deductum (Greene) Jepson and var. scapigerum (Eastw.)
,Jepson in the Sierra Nevada, var. westonii (S. Stokes) J. T . Howell on the edge of
the Sierra Nevada in Inyo Co., var. pubgorum Benth. in DC. in northeastern
California, and var. nudum in northwestern California provided a ready avenue
for its distribution. I n Mono Co., California, it sometimes uses E. elatum Dougl.
ex Benth., a related species.
Euphilotes enoptes enoptes produced a n array of subspecies in California. In the
southern Coast Range, E. enoptes tildeni evolved on Eriogonum nudum var.
nuriculatum (Benth.) Tracey ex Jepson, having its origin most likely from
populations of enoptes enoptes on E. nudum var. paucgorum or var. deductuni. It is
likely that such a differentiation initially occurred in the Transverse Ranges
with the geographical isolation permitting the successful development of the
subspecies. To the north E. enoptes bayensis is a logical extension, the var. nudum
being a plant of more moist habitats on the northern Coast Ranges than var.
aurzculatum of the drier inner foothills to the south. T h e ultimate expression here
is E. enoptes smithi. I t occurs on E. latifolium Smith in Rees, a species closely
related to E. nudum. T h e subsequent use of E. ParvzJorum Smith in Rees by smithi
is probably a matter of a localized host switch. T h e latter plant species belongs
to the E. fasciculatum complex and as such is rather primitive. There seems to be
no racial differences between the butterflies on E. latzfolium and E. parvijorum.
O n the eastern slope of the Sierra Nevada Euphilotes enoptes langstoni
differentiated on Eriogonum kennedyi var. purpusii. This host is related to E. wrightii
var. subscaposum S . Wats., one of the minor hosts used by E. enoptes enoptes.
Euphilotes enoptes mojaue is commonly associated with the annual Eriogonum
pusillum. It is thought that prior to the formation of the Mojave Desert in Late
Pleistocene and Early Holocene times, populations of E. enoptes enoptes occurred
on populations of E. nudum that were situated on the margins of the newly
forming desert region. As the environment became more arid, and the
population density of E. nudum decreased, a switch occurred onto the annual.
The resultant butterfly was then able to spread across a broad area of what is
now south-eastern California and southern Nevada, differentiating, increasing
its range and density relative to the increase of E. pusillum. The combination of
host switch and limited range of overlap between varieties of E. nudum and
E. pusillum provided for the rapid evolution of mojaue from enoptes. Currently, at
Jawbone Canyon and in the El Paso Mountains of Kern Co., along the western
margin of the Mojave Desert where E. nudum occurs, a now distinctively larger
expression of mojaue is sometimes associated with that plant. Interestingly,
SEQUENTIAL EVOLUTION OF EUPHILOTES ON ERIOGONUM
85
individuals of mojaue on E. nudum differ slightly from those on E. pusillum.
Perhaps the present-day butterflies on E. nudum are representative of the early
stages of differentiation of mojaue from enoptes, or these individuals represent the
re-establishment of mojaue onto E. nudum. Sometimes larvae of E. enoptes mojaue
have also been found on large plants of E. reniforme at Sheephole Pass on the
Mojave Desert where E. pusillum does not occur locally, and one attempted
oviposition was observed on E. nidularium Cov. in Clark Co., Nevada.
T h e evolution of Euphilotes enoptes ancilla involved a major host switch from
species involving Eriogonum subgenus Eucycla to the subgenus Oligogonum. This
subspecies occurs primarily on varieties of E. umbellatum, especially the var.
neuadense Gandoger of Nevada, var. aureum (Gandoger) Reveal the higher
elevation expression in Nevada east to Colorado and Wyoming, and the var.
umbellatum in Utah and Colorado (and probably elsewhere, as the var.
umbellatum is found further to the west and north). An unnamed subspecies near
ancilla occurs in the Spring Mountains of Clark Co., Nevada; it occurs on
E. umbellatum var. subaridum S. Stokes. Eriogonum heracleoides is also used across
the northern part of the subspecies’ range. I n west-central Nevada, ancilla has
been found associated with the narrowly endemic E. lobbii var. robustius.
Elsewhere, populations have been found on other species. The most significant is
another host switch event in east-central Utah and western Colorado where a
smaller form of ancilla is found on E. ovalzfolium var. ovalifolium, a host plant
belonging to the subgenus Eucycla (Shields, 1977a).
T o the north, Euphilotes enoptes columbiae differentiated on Eriogonum heracleoides
and E. compositum, both members to the subgenus Oligogonum, whose primary
distributions are to the north of that of the major varieties of E. umbellaturn used
by ancilla.
Occurring to the west and north of Euphilotes enoptes ancilla is E. battoides
glaucon, with the latter probably evolving from the former by a combination of a
host switch to another species of Eriogonum subgenus Oligononum and by
genitalia modification. For the most part the two subspecies are allopatric in
their distribution (Table 7). Presumably the bifurcation of the male valvae in
the E. battoides group of subspecies compared with a more spatulate valve in the
E. enoptes group afforded a degree of genetic isolation in their respective
evolutionary histories. Certainly this factor, coupled with the use of host plants
belonging to two separate subgenera in Eriogonum, added to the isolation of the
species.
The subspecies glaucon occurs sympatrically with Euphilotes enoptes columbiae in
the Pacific Northwest, but the two rarely share the same host where they occur
together, and to a degree their hosts are dissimilar. Euphilotes battoides glaucon is
associated mainly with varieties of Eriogonum umbellatum in California and
Oregon, and on varieties of E. heracleoides in Washington and Idaho. Shields
(1977a) also reported it on E. sphaerocephalum Dougl. ex Benth. var. halimoides
S. Stokes and E.Jlavum var. piperi (Greene) M. E. Jones. Distinctive populations
of glaucon occur on plants of E. umbellatum var. subaridum near Westgard Pass
between the White and Inyo mountains in Inyo Co., California.
T o the west of glaucon and higher in the Sierra Nevada is Euphilotes battoides
battoides, an isolated subspecies that switched from species belonging to the
n = 20 Eriogonum umbellatum complex to the n = 17 E. marzfolium complex. T h e
range of battoides battoides is encompassed by the Pleistocene firn line (see Hill,
86
0. SHIELDS AND J. L. REVEAL
197.5). T o the east of the California range of glaucon is E. battoides baueri. This
subspecies made a major host switch, moving from species of Oligogonum to
varieties of E. ovalijolium, a species of the subgenus Eucycla. In the Sail
Bernardino Mountains, however, baueri uses E. kennedyi var. kennedyi.
Euphilotes battoides intermedia and oregonensis both use Eriogonum marlfolium as
their primary host, and both evolved from glaucon. T h e two subspecies are
isolated from one another, and can be distinguished only with difficulty. The
subspecies intermedia is found along the backbone of the northern Sierra Nevada,
u.hile oregonensis is restricted to the Crater Lake area in Klamath Co., Oregon.
'The distribution of E. marzfolium in northern California is scattered north and
!vest of the Sierra Nevada where it is common, and it too is disjunct with
populations at Crater Lake. O n the pumice sands of Crater Lake, where
oregonensis is common, E. margolium is abundant. Certainly the isolated nature of
oregonensis has permitted its differentiation into a different subspecies, and citing
again the principles associated with the Wallace Effect (Grant, 1966, 1981), the
lack of marked morphological characters is not surprising. The localizccl
endemic, E. battoides comstocki, occurs on E. umbellatum var. furcosum Re\.eal. I t is
probably derived from E. battoides intermedia (Shields, 1975).
The relationship of Euphilotes battoides centralis to other subspecies of E . hattoide.,
is somewhat unclear. With its isolated distribution in the Rocky Mountains and
its switch to Eriogonum jamesii, coupled with its somewhat distinctive phenology,
i t has been difficult to associate with other extant subspecies. T h e key to its
origin may be in the occasional use ofE.JEauum var. piperi. This host plant rang's
from Washington and Oregon east to western Montana where it is replaced by
var. Javum. I n the southern Rocky Mountains of Colorado, E. j a u u m var. J a w m
and E. jamesii var. jauescens S. Wats. are often difficult to separate. If crnlraliJ.
originated from the more northern populations of glaucon, perhaps utilizing
E. j l a m m var. piperi, and then switching to E. jamesii var.Javescens after migrating
southward---not in the Sierra Nevada but down the Rocky Mountains-this
might account for both the distinctiveness of centralis and its association with its
particular host. The use of populations of both var. Jlauescens and var. jamesii--as
the two overlap in their ranges in parts of Colorado-may be easily explained.
Perhaps the reported population of centralis in Lincoln Co., New hlexico, is 011
E. jamesii var. wootonii Reveal. Finally, Shields (1977a) reported markedlydisjunct populations of both glaucon and centralis, each in the Lricinity of the
other's native range. T h e significance of these disjuncts is still unknown. A case
can also be made for the derivation of centralis from intermedia (Shields, 1977ai,
with intervening populations now extinct. A close relative of intermedin, namely
comstocki, also exhibits such a disjunction between southern California and
central Utah.
The evolution of Euphilotes bernardino allyni from E. rnoptes smithi involved a
major genitalia modification coupled with geographical isolation even though
both use the same host species, Eriogonum parvzfolium. Euphilotes enopks smithi is
restricted to the Monterey Co. area of coastal California, while allyni is found in
Los Angeles Co.
While Eriogonum paruifalium is a species that is generally restricted to coastal
environments, arid therefore restricting the potential distribution of the
butterflies associated with it, the range of E. fasciculatum is significant. Eriogonum
.fasciculatum is composed of several varieties that range from the off-shore islands
SEQUENTIAL EVOLUTION OF EUPHILO TES ON ERIOGONUM
87
and immediate coast of California and northern Mexico across southern and
central Nevada to south-western Utah, central Arizona and into Sonora and
Baja California Sur, Mexico. The coastal phase in California is var. fasciculatum
( n = ZO), while that of the southern Coast Ranges is var. foliolosum (Nutt.)
Stokes ex Abrams ( n = 40). In the warm deserts are the somewhat pubescent
var. polzfolium (Benth. in DC.) Torr. & Gray and generally more glabrous var.
Javovirde Munz & Johnston. While the two varieties (both n = 20) have
overlapping ranges on the Mojave and Sonoran deserts, only var. polifolium is
found in the northern Mojave of California, Nevada, Utah and most of Arizona.
Euphilotes bernardino bernardino occurs on Eriogonum fasciculatum var. fasciculatum,
var. foliolosum and the western and more northern populations of var. polifolium.
Toward the northern edges of the range of var. polzfolium, bernardino switches to
shrubs of E. heermannii var. humilius. Populations of E. bernardino on E. cinereum
Benth. from Malibu to the Ventura Co., California, line are intermediate
between allyni and bernardino.
T o the east of Euphilotes bernardino bernardino is E. bernardino martini. This
subspecies only occurs on Eriogonum fasciculatum var. polzfolium. The range of the
butterfly is restricted to the eastern Mojave Desert southeastwardly into southcentral Arizona. A blend zone between bernardino and martini occurs in Morongo
Canyon and up to 2150 m elevation in the eastern end of the San Bernardino
Mountains.
Euphilotes bernardino ellisii appears to be derived from E. bernardino martini
rather than from E. battoides centralis. Occasional specimens of ellisii are similar
to martini, but are larger in size, although specimens of martini from Pima Co.,
Arizona, are also large-sized. Euphilotes bernardino ellisii-martini-like specimens fly
in May in the Buckskin Mountain area of Kane Co., Utah, and are the first
evidence of a spring brood of ellisii. Euphilotes bernardino ellisii primarily is found
on many (but not all) varieties of E. coymbosum, and occasionally on specimens
of E. batemanii M. E. Jones and E. hylophilum Reveal & Brotherson. Finally, in
the Providence Mountains, E. bernardino ‘Eastern Mojave’ occurs primarily on
E. microthecum var. simpsonii in the fall of the year, and secondarily on
E. heernanii var. humulis. This unnamed subspecies is thought to be derived from
ellisii and is found in the Providence Mountains, the New York Mountains, and
the Mid Hills of San Bernardino Co., California, and on the southern end of the
Spring Range in Clark Co., Nevada.
Overall, the flight time of Euphilotes rita is from July to September, but that of
more advanced sibling species, E. enoptes, includes the spring months through
October. Euphilotes bernardino flys in the spring of the year (bernardino, martini) or
from August through September (ellisii, bernardino and ‘Eastern Mojave’).
Euphilotes battoides flies primarily from June to August.
A tentative picture of recent evolution of Euphilotes can be reconstructed. The
Chihuahuan and Mojave deserts did not form until about 11 500 years ago. Salt
cores indicate a major drought occurred 10000-12000 years ago in the
Intermountain Region (Stutz, 1978) possibly when E. rita mattonii evolved on
Eriogonum microthecum then located well to the south or in situ in what is today
northern Nevada. This was followed by a brief pluvial period. During the
Hypsithermal Interval in the American West, the Anathermal (9000-7000 y.
B P ) was subhumid and subarid, with the Altithermal (7000-4500 y. B P ) hot and
dry, and the Medithermal (2500 y. B P to present) cool and dry (Reveal, 1980).
88
0. SHIELDS AND J. L. REVEAL
The effects of the Hypsithermal moved gradually northward through the
Intermountain Region during the Altithermal, or about the time E. enoples and
E . battoides evolved and diversified as they show a generally northward pattern
of distribution. Euphilotes rita shows a southward pattern of distribution that
must have occurred during the earlier Anathermal. T h e eastward dispersal of
E. bernardino on advanced species of Eriogonum subgenus Eucycla suggests a
different pattern that must have been more recent than E. enoptes (e.g.
Medithermal times).
SUMMARY
The relationship between the butterflies of the genus Euphilotes and their host
plants belonging to the genus Eriogonum is not one of coevolution (Janzen, 1980)
but of sequential evolution (Jermy, 1976). While Eriogonum has had a long
history of species development, the present-day distribution of those plants was
greatly influenced, at least in western North America, by glaciation events
during the Pleistocene, especially the most recent Wisconsin stage. The
evolution of Euphilotes as a distinct genus antidates the establishment and
proliferation of Eriogonum. The evolution of the majority of subspecies probably
occurred during the Late Pleistocene in concert with the freeing of the Sierra
Nevada of ice and the development of warm deserts. Even so, it is likely that at
least E. enoptes mojave, one of the more advanced subspecies of that species, did
not become established until the formation of the Mojave Desert during Mid to
Late Holocene.
Unlike the genus Eriogonum which is composed of several distinct subgenera
and nearly 250 species, the species of Euphilotes are only weakly separated from
one another and are here regarded as ‘sibling species’. The specific host
requirements of Euphilotes taxa, coupled with their generally allopatric
distributions, have led to the formation of a series of populations some of which
can be recognized as subspecies but others which are still in the process of
evolving. That the host plants have acted as ‘islands’ is evident. Where
speciation has occurred in Euphilotes it has been on the same host plant where
there has been both a modification in the genitalia and a subsequent separation
of the resulting species onto different parts of the host plant’s range.
T h e evolution of subspecies throughout Euphilotes has been primarily one of
host switching, that is, the establishment of a population of Euphdoles on a
different host from its ancestral type followed by phenotypic differentiation. In
the less advanced species, the switching has always been from one species to
another, but in more advanced E. bernardino and E. battoides there has been only
limited host switching, the significant factor here being geographical isolation
onto isolated populations of the host. The evidence indicates that these processes
are still ongoing as there are several scattered populations in various subspecies
that are on new host plants of limited geographic range that are either
morphologically not distinct or are only weakly differentiated morphologically.
ACKNOWLEDGEMENTS
LVe wish to thank Drs T. J. Cohn, W. Dierl, J. F. Emmel (M.D.), C. D.
Ferris, N. E. Gary, K . Johnson, R. H . T. Mattoni, D. D. Murphy, J. A. Scott,
SEQUENTIAL EVOLUTION OF E U P H I L O T E S O N E R I O G O f l U M
89
R. F. Thorne, R. W. Thorp, D. M. Wright (M.D.), and Mr R. Bailowitz,
J. Lane, G. Pratt and F. T. Thorne for criticisms, suggestions, and/or
information; Dr T. C. Emmel for Euphilotes chromosome counts, and Dr L. D.
Miller and Allyn Museum of Entomology for generous support of field work
(O.S.).Discussions with Mattoni have been especially enlightening. C. R. Smith
of the British Museum (Natural History) in London kindly reported museum
data for Paleophilotes triphysina and Praephilotes anthracias, and Dr Y. P.
Nekrutenko and Mr J.-C. Weiss provided some field data on P. anthracias. Mr
C . Seymour assisted with determining some localities on maps. Work on
Eriogonum (J.L.R.) has been supported by National Science Foundation grants
(GB-22645 and BMS 75- 13063). This is Scientific Article A451 1, Contribution
No. 7504, Maryland Agricultural Experiment Station.
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APPENDIX
Paleophilotes lriphysina Stgr. (north-western China, southern Russia): 1 . Issyk-Kul (lake, 42"30", 77"30'E),
5300 ft, N. Tyan Shan, Kirgiz SSR (BMNH). 2. Kuku-noor ( = Koko Nor, Kuinoor, Ch'ing Hai), 10500 ft,
Chinghai (Forster, 1938). 3. Altyn T a g ( = Astin Tagh), south-east Takla Makan, eastern Turkestan,
Sinkiang (Mattoni, 1977). 4. Kaschgar District ( = Kashgar, Sufu), (39"29', 75"59'E) Tasicre, Sinkiang
(Staudinger, 1891; BMNH). 5. Alai Mts, Russian Turkestan (BMNH). 6. Kizyl (38"43', 66"44'E), Turkestan
(BMNH). 7. Unknown localities: Amoor; Sura (BMNH).
Praephilotes anthracias Christ.: 1. Kuldaha ( = Kuldja), (43'54'N, 81"21'E), Thien-Shan ( = Tyan Shan),
north-western Sinkiang (Mattoni, 1977; BMNH). 2. Krasnovodsk (40"00", 52"50'E), Turkmen, southwestern Russia, May (T. L.). 3. Kirghiz Steppe, Kazakhstan, in the spring (Seitz, 1906). 4. A common
butterfly in the Karakum Desert, ( = Peski Karakumy Desert), Turkmen, south-western Russia, May
(Mattoni, 1977, fide Nekrutenko). 5. Repetek (38'34", 63"l I'E), 185 m, Turkmen, south-western Russia,
early April (Mattoni, 1977). 6. Bukhara (39"31'N, 64"22'E) (BMNH). 7. Aschabad ( = Ashkhabad),
37"57'N, 58"23'E), 220 m, Turkmen, south-western Russia (Forster, 1938; BMNH). 8. Kopet-Dagh (Mts),
Descht (37"28", 58"29'E), north-eastern border of Iran (BMNH). 9. Kain, 2000 m (33"42", 59"5'E), Iran,
mid-March (Carnegie Mus.). 10. Syr-Darya, Baigacum, Turkestan (BMNH). 1 1 . South of Rui Khaf,
Najmabad Plain (34"32'N, 60"4'E), Iran (BMNH). 12. Kyzyl-Kum, Turkmen (BMNH). 13. West of Deynau,
Amu Dar'ye, Turkestan (BMNH). 14. Chehal, Tekes-He River, Kazakhstan (BMNH). 15. Unknown
localities: Usunada and Hdg (BMNH), Hyreana (Weiss coll.). 16. Hyrcania ( = Astrabad province), southeast shore of Caspian Sea, Iran (Weiss coll.).
Micropsyche ariana Mattoni: Mt Khwajaghar, Koh-i-Baba Mts, 3600-4000 m, Afghanistan, mid June-early
July (Mattoni, 1979).