StephenJ. Novak and AngelaY Welfley,Departmentof B o ogy Bo se StateUn versty. T910 Un versty Dr . Bo se
daho 83725
GeneticDiversityin the lntroducedClonalGrassPoabulbosa(Bulbous
Bluegrass)
Abstract
Buibous bluegrass(Po.r,x/r.)r.r) is a perennialhunchgrassrlith a r\idespreaddistfibution throughout itli nrtire frnge in Europe
and the \{editenanean. This grass has been iniroduced rnto North Americr and nou occurs thfoughout nNch of the lr,esiern
Unned Siate\. Within ils nrtive range,bulbous bhrcgrassreproducesmainl_vthrough selual means;hore|er, in North AJnerica
clonal reproductionoccurs prinllrily throuSh the production of \cgctalilc ffucturcs callcd bulble!s. High chromosomc counls
are frequendy repofied f(r this speciesand suggestit is apolyploid. To asscssthc lc\'cl andpailcm ofgcnetic divcrsjty ofbulbous
bluegrassacrossaportion of its intfoducedrange,a totalof l0populations lioln Idaho. Orcgon.andwashinglon wcrc analyzcdby
staining for 1,1enzlnles rhar $ere coded fbr br- l9 genedcloci. R.sults indicalc that bulbous blucgrassconlains lishcr lcvcls of
generic v iation than expectedfor an irrroduced cloial planl spccicsr27.9% of loci are polymorphic per populadon. wilh an
ofallindiliduals withinthese
avef.rgo
e f 1 . 5 , 1 a l l e l epse r l o c u s .i r n da n c a n o b s c r v c dh c t e r o z y g o s i to! f 0 . 2 0 2 . O n a v e r a g e , 6 4 %
populrtions possessthree or lbur rlleles al onc ornorc locira valueconsistentwith previousrepo(s for auiopolyploid species.r\
per population. The
rotal of 8'+ muhilocus genotypes\lere detectedi thesc l0 populations.!r'i!h an alerage of 9.6 genot_vper
nunrberand complex distfibution of multilocus genLrtr-pes
obsened in this stud."may bc thc rcsult ofmultiplc inlroductionsoflhis
speciesinio its ner\ range.and/or occasidral \exual reproductionuillin introducedpopulatil,ns.
lntroduction
Biologicalinvasionsare deflnedas the successful introduction and establishmentof an organism into a regionor habitatthat was previously
unoccupiedby that species(Mack 1985). Biological invasionscan vary geographicallyliom
simple range extensionsto intercontinentalnrigration (Barrctt and Richardson1986). Success
ful invaders(whetherthey be plants or animals)
often possessthe ability to aggressivelycolonize
a neu territory.u ith rlpid rungeerpun.i,'nrcr,''r
the jntroducedregion (Mack 1985.Barrettand
Richardson1986,Barett andShore1989).Once
invasionsoccur,they canposeongoing problems
becausethey can act as vcctorsfor disease.be
expensive.alter ecosystemprocesses.and reduce
biologicaldiversity(Vitouseket al. 1996). In
addition. severalrecentrcviews have fi)cusedon
theissueotbiological invasionsastbrccslbr global
change(D'Anlonio andVitousek1992.Vitousek
e r r l . l q q 6 ) . A d d i r i o n a l l Si n. y 3 . j r q. p e c i e .p r u vide biologistswith excellentmodelsystemsfor
genetic and evolutionary studies (Baker and
Stebbins1965.Barrettand Husband1990). In
vasive plant speciesare commonly reported to
possessuniparentalreproductivesystems,be polyploids.containdcpauperate
levelsofgenetrcvana
rAuthor for correspondence.
tion within populations,have high levels of ge
neticdiff'erentiation,andexhibit multibcus structure amonginffoducedpopulations(Baker 1974.
Bro* n andMarshall1981, BarrettandRichardson
1986).
Traditionally,introducedpopulationsare believed to be establishedby only a srnall number
ofienresultingin a lossof genetic
of imrnigrants,
variation through sampling elfects (Barett and
Richardson1986.Barett and Shore 1989). ln
additionto lbundereflectsandgeneticbottlenecks,
an absenceof repeatedimnrigrationeventswill
contributsto high levelsof geneticdiffcrentiation amongpopulations(BrownandMarshall1981.
Wade and McCauley 19ii8). Conversely,rnultiple introductionsof different genotypesat the
sameor nearbylocationscan result in greater
geneticvadation in founder populations(BalTett
andHusband1990).Recentgenetic
evidencetbr
cheatgrass(Btonus tectorun L.) and white bryony (Bryoniu albttL.) suggeststhat nultiple introductjonsof alien speciesmay be mQrecommon than previously thought (Novak et al. 1991.
NovakandMack 1993,Novaket al. 1993,Novak
and Mack 1995).
Uniparentalreproducti\esystems,suchasselfpollination or clonal reproduction (i.e. agamospermy and vegetativepropagation).cln be a
beneficialcharacteristicfor inmigrants. and are
Vol. 71, No..1. 1997
North$'estScience.
a : rl q e . r b ) t h . N o n h " c ( S . i c . r l i . l $ . . f t o n . \ l l i ! h ( . . $ \ . , 1
271
commonamongspeciesregardedashighlv successfirlcolonizers(Stcbbins1957.Brown and
Marshall 1981). Seltingard clonallyrcproducing speciesare capableof producingprogeny
without the presenceof a mate which. I ) fiees
them ti-on the dependcncyof pollinators,2) ensurcsreproductivesuccessdespiteunlavorable
conditions,3) preser-res
adaptivegcnecomplexes
tirr all jndividuals within the population,and 4)
allowsa singleindividualto startanentirecolony
or invasion(Stebbins
1957,Williams
1975.Banett
and Richardson19136).
With clonalreproduction,
progenywill beidenticalto theirparents.andtherefore. some modelssuggcstthat clonally reproducingspcciespossess
little orno genotypicvariation u'ithinpopulations(Williams 1975).Howoer,
a second-qroupof modelsclaim that the level of
geneticdiversityin clonalspeciescan.in fact.bc
similalto scxualones(MaynardSmith 1971,Lynch
198,1.Ellstrandand Roose 1987). This sLudy
examinesthe level and structureofgenetic diver
sitf in thc clonallyreproducingintroducedplant
species bulbous bluegrass(Pou bulbosa L.1
(Poaccac).
StudySpecies
Bulbousbluegrass
displalsmanyof the ecologi
cal chalacterislics
of a successtul
invasivcplant
specics.This perennialbunchgrassis widespread
throughout $,esternEurope and the Mediterraneanregion(Cronquistet al. [977), and is more
rarely distributcd in southemand easternBritain
(Humphries1979).It is comnonly foundrvithin
pastures.roadsides.and othcr disturbedareasat
low to middleelevations
(Cronquistet al. 1977).
Bulbousbluegrass
was introduccdin the eastem
United Statesin 1906(probablyliom Russia),
andit u'asintroducedin thewestemUnitcdSates
in I9l 5 asa conttminantin alfaltaseed(Harrison
et al. 1996).Follou'ingits introductionin theWest,
this grassquickly spreadthroughoutmuch of the
IntemountainWcstbecauseitis aggressive.
highly
competitive.persistent.
andcanbecomea domi
nant speciesin hcavily disturbed(overgrazcd)
habitats(Harrisonet al. 1996).In addition.rapid
rangc cxpansionof bulbousblucgrassu'asfhcili
tatcd by the purposefulinlroduction of the grass
to prevent soil erosion or contr(t mole troublesone weeds(YoungerandMcKell 1972). Samples
havc been collected in New Vrlk. Nofih Carolina. Virgiria. North Drkota. Oklahoma,andnrost
$cstcrnstatesincludingCalilirrnia,Oregon.Wash272
Novak andWelflev
ington. Idaho. Montana. Wyorning, Utah and
Colomdo(Hitchcock1971).
Althoughbulbousbluegrasschieflyreproduces
throughsexualmeanswithin its nativerange.it
is primarilyanasexuallyrcproducingspecieswithin
North Arnerica where clonal production of
propagules.or bulblets, have replaced the plo
ductionof seeds(Hitchcock1971.Youngerand
McKell 1972.Cronquistet al. 1977). Also, bul
bousbJuegrass
possesscs
severalbulbousbases,
\\ herecachbir\ei. \'uprbleolpir ing ri.e r,' I neu
plant ifdetachedanddispcrsed(Humphdes1979).
Although high chromosonecountshave been
reportedfor bulbousbluegrass(2n = 213.35. :12).
suggestingthat it is a polyploid,the literaturedoes
not indicatethe type of polyploidy that occurs
within this species(Cronquistet al. 1917).
lnvestigatingthe populationgeneticsof an
invading speciesmay provide insights into the
natureofits il'rtroduclioninto its new range. With
this paper.\\,ereport resultsfrom our analysisof
l0 populationsol bulbousbluegrassfrom Idaho.
Washington.andOregon. The specificobjcctives
of this study wcre to; J) determinethe level and
structureof geneticvariation within and among
populationsusing enzymeelectrophoresis,2) as
sessthe pattern of genctic variation and dctermine if they provide insightsinto introducrion
dynamics(singleor multipleintroductionsevents).
3) cornpare
theresultsobtainedtbr bulbousbluegrassto othcr studiesof introduccdand clonally
rcproducingplant specics,and4) and determine
the genetic consequencesof polyploidy lirr this
spccies(i.e..type of polyploidy).
Materials and Methods
P a n t C o l l e c to n s
As a first effbrt to describcthe geneticvadability
oi bulboub
. l u c g r . r . l\ e. n l o c r l p o p u h l i n \ \ \ e r c
collectedfrom variouslocationsin ldaho.Oregon.
andWashington(Figurel. Tablel). Population
collectionswere madebetweenJuneandAugust,
1996.typicallyin disturbedhabitatssuchas vacantlots and alongroadsides.ln addition.these
populationsalsovariedin their sizeand dcnsity
(Table l). The paniclesofthifiy to ti)ftv separare
individualsin eachpopulationwere collcctedat
rcgularinternals(approximately1 m) while walking throu-qhthe populationandstoredwithil separateenvelopes.Paniclesu'erehan'estedwhenthey
-r'
Washington
T'
I
I
\
I
:1'1
r
I
)
. l
BC
a '
SAL
,/
\
l^
( BSU
a
o
STAN
r^-21
ldaho
i
a
I
PV
a
origon _
TF
----T
r
POC
--'r------1
l
I
ligure L N'l.rt of ldaho. Orcgon, and \\h\h ington. sho$ ing the loc ationsof rhe | 0 populalionsof bulbour blucgrrss sampledand
anrl!zed in rhjs !lud]. SceTable I fof namesof \ampled site\ corre\ponding Io rhe populalion abbrc\ia(ions.
lABl-E
Slalc
l. Collection datafor bulbousbluegrasspopul.rtioniro ldaho. Oregon.andWashinglon.popularionabbre\iarions and
a gcncral descriptionof rhe !i7e. dcnsil). and hrbital condjtron\ ol c,rchc(rllecnonste.
Countl
l. Adr
Populaliol1
Abbre\iation
BSU
5. Custef
B o i \ e - B o i s eS t a t e
U versit!
B0ise PleasrntValley
Iioad
T$ ir F.rlls
P0c.rtello
Sranlc)
6. Lemhi
Salmon
SAI-
7. Bakel
E. Lmarilla
Brk.-r Citi
BC
P[\
9. Whiuran
1 0 .C r a . l
Pullm.Ln
N,losesLake
PLILL
IlL
L Ada
3. Twin ftrlls
Ofegon
l-ocation
PVR
TF
POC
S IAN
P0pulati0n
Dcscription
large.high densit)' running path along the Boise ltilcr
behind Boisc Sule Uni\,ersit,v
hfge. high densjly.dlongPleasanrVallc! Roadnearldaho
SrurePenitentiary
mediu . noderate densitv.hencad o\erpass
slnall. moderalcdcnsity. \,rcanr lot
nxxlefate. moderatcdcnsilr. difi road or rvcn side of
Salmon Riler at Hcll Rorring lo$,ef trailhead
sm.rll.lo$ densit,v.roadsidenear lacanr lot
large.high densi!-. cofner hillsidc lot
moderaie,high densit] fordside near Ersrern Oregon
S u t e C o f r e c t i o n aIln \ l i t u l e
moderarc.moderatedensiry.E.H. SreftenCenrer
lafge. nrodcratedensity.di\urbed sagcbrushhrbitar
GeneticDiversityin BulbousBluegrass 2i3
containedmaturebulblets.Maturebulbletsare2
broad,shiny.dalk puple
nrmin length.andpossess
, , r b l r e k h a . c . u i t h p r , ' t r u J i n g[ . r l i u c e , r ut irp : .
One bulblct from eachindividual in a populatlon
wrs randomly-selectedand placedon moistened
filter paper in r pcLridish. To break dormancy,
bulbous blucgrassrequired a chilling treatment
consistingof incubatingbulbletson rnoistened
filterpaperrt5 C lor.l 5 days(Ball etal. 1995).
Adclitional water \vas applicd as neededto prevent desiccationof the bulblets. Atier chilling.
pctri dishesrvereincubatcdat room telnperaturc
with noderate sunlight.u,ith bulblets usuallv
' germinating"within2.1hours."Secdlings"were
permiltedto glow tbr approximatelyone week,
prior to geneticanrlysis.
G e n e t i cA n a y s s
Enzymc clectrophorcsiswas pcrlormed according Lorhe nethods of Soltiset al. (1983). Harvested seedling"tissuewas maceratedin lisHCL grinding bulTer-PVP soluLion. Final
in the grindconcentlation
ofPVP (Mw ,10.000)
ing butler was l2% (u,y'v).Starchconcentration
of the gels was 12.5%(w/v). Enzymerctivity
(ADH). aldolase(ALD).
tbr alcoholdehydrogelase
glulamate dehydrogenasc(GDH). glutamate
(GOT), malic enzyme
oxalacetate
transarrinase
(PGI).andtriose
(N{E),phosphoglucoisomerase
phosphateisomerase(TPl) were visualizedusing buffers)'stcnr8 (Novaketal.1991).Enzyme
-phosphatedehydrolctivit!' for gl) ceraldehydc-3
(lDH).
genase(G3PDH).isocitratedehydrogcnase
(MDH). phosphoglucomunalate dehl'drogenase
dehydrogcnase
tase(PCM). 6-phosphoglucorate
(6PCD). and shikin.rate
(SkDH)
dehydrogenase
were visualizedusingbuffersysteml; u'hileendehydroz)'meactivityiirr glucose6 phosphate
(MDH),
genase(G6PDH), rnrlatc dchydrogenase
(PGNI)*'crc visualized
iud phosphoglLlconutase
usingbutlersystem9 (Soltis.et al. 1983). Reliableinterpretationollhe bandingpatternsof MDH
and PGN,Iwas obtainedb) comparilg results
obtainedirom both systemI and systen 9. Enz1'mestaining proceduresfollou'ed the mcthods
exccpLibr ADH, rl'hich
of Soltis et al. ( 19133).
followcd Hautler (19E5). ALD and TPI were
stainedusing the agaroscoverla,vmethod.
Enzl-lnebandingpatterlsfor eachindividua]
were recordcd.irndgenotypeswere intered based
on kno$n enzy[re subunitstructurcand conpafi
mentalizationlor diploid seedplants(Weedenand
211
Novirk and $lelflc!
Wendel 1989). However,the complexbanding
pattemsobsen ed lbr bulbousbluegrasswere not
but inconsistent*'ith diploid geneexpression,
stcildwere more consistentwith the paftemspreplanttaxa(Sdtis
viouslyrepoftedfor autoteftaploid
1986;Sottis
andSoltisl988,Soltis
andRieseberg
and Soltis 1989a,Soltisand Soltis 1989b,Wolf
et al. 1989). Becauseof thesesimilarities.u'e
rssumedthatthepopulationsofbulbousbluegrass
analyzedir this study are autotetraploid,and ass i g n e Jg e n o t v p ch. a . < do n t h e r e l r l i \ c s l J i n i n g
intensity and numberol enzymebandsscoredat
eachpolymoryhic locus. Additionally, we rcanal 1 z e ,m
J l n l i n d i \i d u i r l t. o e n . u r el h r l r \ u ri l s \ i g n
mentsofgenotypes,basedoIrthecriteriadescribed
above.$ ereconsistent.
Geneticdiversityfor all l0 populationsof
usiltgthe mean
bulbousbluegrasswas assessed
nurnberof allelesper locus(A).the percentpolymorphicloci per populati{)n(%P) andtheobsen'ed
mean heterozygosity(t1,,). A locus was detined
rs beingpolymorphicifone or moreindividual(s)
within a population possesseda genotype that
differedliom otherindividualsin that population,
t yl .
d l I h . rl o c u 5O
. h . e r \ e dr n e r nh c l e r o z l g o s i w
determinedby the direct count method. Mean
values for A and 7,:,Pfor all ten populationsof
bulbousbluegrass,at both the speciesand popuIation levgls.rvereconpared to the mean values
ofA and%P compiledby HamrickandGodt (1989)
from over 400 publishedstudiesof plant species
Becausean auusing enzymeelectrophoresis.
totetraploid individual can naintain as many as
three or four alleles at a single locus (due to tetrasomicinheritance),the proportionof individu
als exhibiting thrceor more allelesat one or more
locus$as calculated1breachpopulation(Soltis
and Soltis1989b).In this study,clonalstmcture
was assessed
by calculating the total numbcr of
as well as the disuniquemultilocusgcnotypes,
tributionofmultilocusgenotvpes
rvithinandamong
populatiors. N{ultilocusgenotypeswereassigned
by exanining their allelic compositionat all polyrnorphickrci.
Besults
GenetcD versty
A trxal of26.1bulbousbluegrussindividualsfronl
l0 populationsin ldaho. Oregon. and Washington were analyzedfor geneticdiversity, with an
averagcof apploximately 26 individuals per
population.All enzymebandsscoredin this study
migrated anodally from the oigin. The 14 en
zymeswerecodedtbrby 19putativegcncticloci.
Across all populations nine of 19 locr (1'7.44/c,)
rverepolymorphic:Adh, G3pdh.Idh-l, Mdh-1,
Mdh 2, Pgi 1. Pgi 2, Pgn l.and,6Pgd-1 (.Table
2): all other loci were monornorphic. Although
the populations
ofbulbousbluegrass
analyzedin
this study generallypossessedsimilar patternsof
allelicvariability,someditlerences
arnongpepulations were observed. For instance.Adlzurwas
(TF,POC.
detectedin only tive of 10 populations
BC. PEN, and ML): whereas.Azllrc occurredilr
all populationsexceptPVR,PEN. PULL. andML.
G-)pdhbwas detectedin only two populations:
T F a n J S T A \ . E i g h l , ' i l 0 p o p u l a t i o nu. e r e
polymoryhic at 1rlir--1,
while PVR andPULL were
hxed lor ldh-la. Only BSU, PVR, and PULL
werepolynorphic at Mdft--1,all otherpopulations
were fixed lor Mdh-lct. With the exceptionof
STAN (which wasfixed forPgi-2c) andPEN (with
both Pgi-2b and P3i-2f , all l0 populationspos
sessedat leastthree allelesat Mdh-2 and Pgi-2.
All l0 populationsrverepolyrnorphicat P3i-l and
6Pgd-i. Finally,six of l0 populations
werepolymorphic at Pg'r-1, while PVR, POC. PULL, and
ML weretixed lbr Pgn'1a.
A total of 3.1alleles were detectedat thr: l9
scoredloci. with a meanvalue of 1.79alleles/
locus for the spccies.Averagedacrossall popu
lations,the meanvaluefol A was 1.5.1,9cPwas
27.9, andH,, was 0.202(Tabie3). The highest
valuesfbrA antla/cP(.l.11ard 36.8%,respectirely) wereobservedin theTF population.The
samevaluetbr |rP (36.8c/r)wasfound in the BSU
and PEN populations.although values tbr A in
the lattertwo populationswere slightlv lower than
TF. By far, the lowest levels of %P (5.3) and A
( L42) wereobservedin the PVR population.even
thoughPVR alsohad the secondhighestF1 r'alue
(0.263).Thc highestvalue(H, = 0.309)rvasde
tectedin the STAN populationwhiie the lowest
valueof 0.124wasobseryed
in the SAL population. Mean valuestbr A and,./r'Pfor all ten
TABLE 2. Allele liequencie\ at nine pollmorphic loci t'orerch populrtion ofbulbous bluegrass. Populationrbbrc\iari|)lrs tre
gi\cn in Tabl. 1.
Populations
STA\
C3pdh
Mtlh-2
Pgi 2
0.E75
0.115
1.000
0.6.1,1
0.356
0.990
0.010
0.317
0.2rJ9
o.0'/'7
0.163
0.15'1
0.250
0.75t)
0.r-)-18
0.111
0.750
0.038
0.911
0.067
0.'123
r.000
I 000
r.000
0.750
0.250
0.:50
0.500
0.:50
0.t50
0.750
0.250
0.250
0 :50
0.250
1.000
0 607
0.193
SAL
tsc
0.069
0.922
0.009
1.000
0.057
0.9,11
1.000
0.052
0.918
1.000
r.000
| 000
0.198
0.E02
t.000
0.179
0.8:l
1.000
1.000
0.012
0.958
1.000
0.579
0.028
0.l,ll
0.01,1
0.236
0.129
0.671
1.000
0..105
0.052
0.lllJ
i).016
0.379
0.1-i0
0.t50
0.015
0.017
0.918
l).r)/ l
0.029
0.912
0.088
0.611
0.t53
o.EEE
0.1ll
0.6t9
0.371
0.819
0.17|
0.138
0.793
0.069
0.8E8
0.lll
0.5r7
0..161
1.000
0.268
0.713
0.009
1.000
0.917
0.081
0.750
0.250
0.036 0.833
0.96,1 0.167
1.000 1.000
0.971
0.029
1.000
0 259
0.r07
0.216
0.103
0.155
0.250
u.150
0.r03
0.009
0.853
0.015
0.9:l
0.78
0.6-18
0.362
0 175
0.0rE
0.t31
0.009
0.366
0.250
0.150
0.ti6
0.080
0.80.1
0 250
0.50
0 69l
0.059
0.250
0.0t9
0.221
0.165
0.735
0 350
0.660
0.r67
0 661
0.167
1.000 0.833
0.161
0.955 0.661
0.0.15 0.311
0 . t1 8
0.882
r.000
0.05.1
0.250
0 500
0.250
0.250
0.75i)
0 239
r-J.186 0.:9.1
0.8l,l
0.,161
0 2i1t
0.02r
0.181
0.010
0 . 2L 9
0.25t)
0.750
0.01r
0.01I
0.918
1.000
1.000
0.6.11
0.359
0.95iJ
0.0.11
GeneticDirersityin BulbousBluegriss 215
TABLE 3. Genetic \.Lfinbiliry \Iatistics lin bulbous bluegfa\s popuLrtions. Description of,.1. '21'. and lJ, are gircn in rhc lcrr.
Proponion reiers to rhe nrulber ol irdniduuls possessingtbiee or lnorc rlleles .rt one of nofe loci in $ese popula
l\{ultilocus
Genotypes
CP
l Boise-BSU
26
1.68
16.8
2. Boisc PVR
]l
29
28
li
1.,11
1.7-l
1.58
r.5l
5.3
36.8
16.3
0.t]
0.t61
0.t13
0.111
0.77
1.00
o.91
0.50
l.l
t9
1.,{2
1.58
I1.6
11.6
0.309
0.1:,1
t.0t)
0.ll
1
1
l
0.r60
-r5
tl
21
L5l
l.17
r.53
0.17-l
0.38
0.11
21
26-1
1.51
0.tll
0.125
0.202
1.00
0.33
061
3. T\ in F,rll\
.1.Pocrlelli)
5. Stlnle)'
6. Sah)10n
Ofegon
7. Brkef Cit)
8. Pcndlelon
9. P llnr.Ln
A1l p0pLrllrtion\
populations
ofbuibousblueglass.
at bixh thespecics and populationlcvcls,wcrc similar to thc
lnean valuesof,1 and 9iP compiled b1'Hamlick
and Codt ( l9ll9) (Table:l).
Thc possession
of loci rvilh threeor morc allelesiit a Iocusis oneofthe geneticconsequeuces
of autopollploicly(Soltisand Soltis 198lJ,Soitis
plants
andSoltis 1989bI. Therefore.autotetraploid
'enz1'me
exhibit
nultiplicity" (i.e..thel produce
nruJtip)e
cnzymctirms. aswell as morekindsof
hybdd enz,vneslbr multimeric enz)'mes). For
thc tcnpopulations
olbulbousblucgrass
anallzed
in this study.enzymemultiplicityu'asobserved
at Mdh-2 antlPgi-2. Evcn thoughthrceofthese
l0 populadonsof bulbousbluegrass(TF. POC.
BC) possessed
threeallelesat,L1lr,lo one indi
vidual cxhibitcdenzymenrultiplicityat this locus. The lneanproportionof iIrdilidualshaling
threeor more allelesat one or more loci tbr all
ten populationsu,as0.6.1(Table3). The highest
proportion( L00) occurreclwithin trl r Idahopopulalions (PVR and STAN) and onc Washin-{ton
-LLl.
r rhi l e t h c l o \ \< . t p r o p o r t i o n
J ' o p u l r t i n rPl I
(0.12)*as tirundwithin the SAI- populationof
posscsscd
ldaho. All tenpopulations
individuals
exhibitingenzvmemultiplicityat Mdl-2 (u'ith a
rnininum offour individualsin SAL). u,hile only
(BSU.PVR. POC.STAN.
tive often populations
and PULLi containedindividualsuith enzyme
multiplicit) at Pgi 2 (data not shown). Every
indir idualin PVR exhibitedenzymemultiplicit)
for both Mdlr 2 ;r'tl Pgi-2.
276
Norak and\\'elflev
36.8
15.8
16.-l
21.9
l2
2
t5
5
11
T,qBLE ,1. Comparisorol genetic\,tLfi.rbilityin hulbousbluegrass$ith other plant species.brsed on enzime
clccrrophorcsr\dr|a. Dir(alorlhe otberplanr\pec i e sr e r e c o r r p i l e db , vH a r n r i c ka n dC l o d l 1 1 9 9 0 ) .
Speciesle\ el
H c f b r c e o u ss h o n l n e d
( l r a \ i ! ] d i s p c r \ c ds c c d !
Aseru.Llrnd sexu.Ll
Errl,,'successi0nrl
r \ 1 1o l h c r p l a . ! s
B u l h o u \h l u e s r a s s
2.i8
l.t2
1.91
l.8l
t.6c)
198
1.96
1.79
59.2
.ll.l
.t8.5
.r3.8
.19.0
50.5
11.1
P u p rL I i , , n1 e \ e l
Herbace0u\\hon'li\ed
Tcrnpcntc pllnLs
Gfa!itv dispersedseeds
A s e \ u a l a n ds e \ u a l
Ead] succes\ional
Al1 other tl.Lnr,i
Bulbous blueSf.rs\
1.66
1..t0
1.51
L.15
1.,17
1.,16
1.53
1.5.1
.10.3
r8.0
_:2.6
298
29.,t
29.6
-1.1.2
)1.9
Clonal
Structure
A btal of E'l nlultilocus genotypeswere detected
\\ithin the l0 populationsof bulbousbluegrass
analyzedin this study (Figurc 2). Se\,enty-six
multilocusgenotypes(90.5{) wererestrictcdk)
o
-
a single(but not the same)population.Six dif
fcrent multilocusgenotypeswere found within
tu'o populations.one genotypewas found within
three,and the most widespreadgenotype,designated#2, occurredin five of the ten populations
(BSU.POC.BC. PEN,andML). The nean number
ofpopulationsthateachgenotypeoccurredrn was
1.17.The fcwestnurnberofmultilocusgenotypes
that occuned within a single population (PVR)
wastwo. while the highesttunber of genotypes
found within a population (PEN) u'as 2.1(Table
3, Figure3). On average.
eachpopulation
ofbul,
bousbluegrassincludedin this alalysis possessed
9.6 multilocusgenotypes(Table3).
"
3
4
5
6
7
5
N u m b e ro t P o p u l a t i o n s
Discussion
Genetc Dlversty
Figure2. Hisrogran illustraring thc distribution of 8.1
l n u l t i l o c u \g e n o t i p e sa m o n g l h e 1 0 p o p u l a t i o n s
o f b u l b o u sb l u e g r a s s .' N u m b e ro f P o p u l a t i o n s '
e q u a l st h e n u m b c ro f p o p u l L r t i o ni sn $ h i c h e a c h
genor\'pe!r'a! dctcclcd.
Our analysisof these l0 populationsof bulbous
bluegrassfrom Idaho. Oregon, and Washington
indicatesthat this speciesdisplayssurprisingly
high levels ofgenetic diversity at the speciesand
Distributionof genotypes
over populations
o
^
c a ,
o
sJ
CL
o
c
I
1
2
3
4
5
6
7
8
9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 22 02 22 13 2 4 2 5
Number of Genotypes
Figure -1. H islogr.rn displa) ing the numbcr of gcnotvpesdetectedin cach of the l {l popularionr of bulbous bl uegrass. populr
! i o n { c q u a l st h e r c t u r l n u m b e r o t s i t c \ \ \ i t h a g i v e nn u m b e ro f g c n o t y p e s .
GeneticDiversityin BulbousBluegrass 277
populationlevel. At the specieslevel.the mean
valuesforA and'/aPreportedlbrbulbousbluegrass
( | .79 arlcl17.4, respectivcly)
are quite similarto
the vaiuesreportedfol other plant species( 1.96
(Table:l).At the popula
and50.5,respectively)
tion level. sirnilarmeanvaluesofA weredetected
tbr bulbousbluegrassandotherplants( 1.53and
while the meanvalueof 7cP
L54, respectively),
bluegnss(27.9)wassomethatlowcr
1br-bulbous
(34.2). Hov'
when comparcdwith other-plants
cver. if the resultsfor PVR and PULL (%P = 5.3
and 15.8.respectively)arc excludedtionr thc
analysis.the valuc of 7cPlbr the remainingeight
populationsof bulbousbluegrass(32.2)is ver-rcompanble to the valucreportedtbr other plants.
are surprisingbecausemost
Theseobservations
of theseother specicsreproducesexually,and
serual spcciesare generallybelieved to possess
morediversitythanspeciesthatreproduceclonally.
With the exceptionofthe valuestbr other mono
cots. bulbousbluegrasshas similar amountsof
geneticdive$ity comparedto plantsu,ith sinlilar
life history characte stics.at both thc speciesand
by Hamrickand
populationlevel.assumrnarized
short-livedperennials,
Godt ( 1989):hcrbaceous
temperateplants.plantswith gravity-dispersed
seeds.plantsthatcanreproduceboth sexuallyand
plants(Table,l).
asexual.andearly successional
Ellstrand1984).andwhltebryony(Br1'oniaalbaNovak andMack 1995).
high levcls
alsopossesses
Bulbousbluegrass
of hcterozygosity(H" = 0.202), and 6,17oof all
individuals, on average,maintainedas many as
three or more alleles at one or more loci (Table
.11.Our lindings.rr. consi.lent\\ ith pre\ i,,u\ rcof au
ports describingthe geneticconsequences
topolyploidy: autopolyploidplants tiequently
posscsshigher levels of hctcrozygosity,because
of enzymc multiplicity. when comparedto dip1986;Soltisand
loid plants(SoltisandRieseberg
Soltis 1988,Soltis and Soltis 1989a,Soltisand
Soltis 1989b,Wolf et al. 1989). Basedon the
results of this study, and the high chromosome
countscommonl-yreponedfor bulbousbluegrass,
it is likely that this speciesis an autopolyploid.
This likelihood pnrbablyexplainsthe higher levels ofgenetic variationreponedfor bulbousbluegrasswhencornparedto the otherintroducedplant
specieslistedabove,which arc primarily diploids.
Further insights into the type of autopolyploidy
exhibitcdby bulbousbluegrasswill be obtained
by performingchromosomescountson the populationsanalyzedin this study.
C o n . i L i e r i nl h
EJ l b u l b o u .h l u e p r l : ri s a n i n troducedplant speciesthat reproducesby clonal
means.the findingsof this studyare madeeven
nore surprising.Low levclsof geneticdiversity
haveofien becnreportedwithin and amongpopulationsof inhoduccdplant species(Brown and
Marshall 1981, Barrett and Richardson1986,
intro
B r r r r r rar n dS h , ' r el q x q ) . e s p e c i J lul )r n , ' n g
ducedplantsthat reproduceclonally (Barrettand
Richardson1986.Barrcttand Shore1989). For
instalce. the lcvel of genetic variation detected
was
ofbulbousbluegrass
in thesel0 populations
higherthanthatreportedt'orintroducedplantsthat
reproduce sexually such as Noogoora burr
(XduthiLltil stronqr i u nt-Moran and Marshall
1978). little jack (Enax spinosa-Marshall and
Weiss 1982),witchweed(Slrlg.r.rri.r/icd Werth
halepense
ct. al. 1984).JohnsonErasslSorghurn
Wanvick et. al. l9E:l;. and cheatgrass(Brorrrrs
te.Inrlrr Novak et. al. 1991,Novak andMack
I ' J o l ) . I n r d J i r i , \ nr.h cl c \ e l o Jl e n e t i e\ c r i r l i o n
in bulbousbluegrasswassubstantiallyhigherthan
the level reportedfor most introducedplantsthat
exhibit clonal reproductionsuchasskeletonweed
(Chontlrillu.junceo-Burdonet. al. 1980).dan
delion (Toru.rucurnrffitirule Lyntan and
Insightsinto the clonal structureofbulbous blue
grassarc providedby exarniningthe number and
distribution of multilocus genotypes.Thc distri
bution ofmultilocus genotypeswithin ard among
populationsof this grassis in generalagreement
with resultsreponed tbr other clonal plant species(for a reviewseeEll strandandRoose1987).
The vast majorityof genotypes(76 of 84) possesseda local distribution,being rcstrictedtojust
a single (althoughnot the sane) population.and
themostwidcspreadmultilocusgenotype(#2) was
detectedin only live ol l0populations(BSU, POC,
BC, PEN, and ML). In addition.none of the
multilocus gcnotypesdetectedin multiple popu
lations appearedto have a strong geographical
pattemto their distribution. However.scvcralof
thesegenotypeswere consistcntlydetectedin eiwiLh
thertheBSU, POC,BC. orML populations,
threc of thesepopulations(BSU. BC. and ML)
locatedin westcrnportionsofthe samplcdrange.
Forinstance,genotype#4wasdetectedin BSU and
ML, genotype#7 was detectedin BSU and BC.
andgenotype#19 wasdetectedin BC andML (data
not shown). The abundanceancldistribution of
thesemultilocusgenoq'pesmay havercsultedfrom
nultiple introductionsof this glassirto the arca
278
Novak and Weltley
C ona Structure
sanlplcdand its subsequcntaccidentalspread.
Altematively,this abundanceanddistributionmay
have resultedfiom multiple introcluctions
and
subsequentpurloscful introduction of thc grass
to preventsoil erosiol'lor control of moretroublesone $'eeds.Puryosefulintroductionsarea more
Iikely meansof spreadbecause
bulbousblucgrass
bulblctsappearto possesslimited dispe$alcapabilities.
Bulbousbluegrassdid not havea singlepopulatior that was uniclonal(Table3). The lewest
number of genotypesdetectedu'ithin a single
population(PVR) was two. while 2,1diflerent
genotypeswcre detectedin the PEN population.
These 2,1distinct genotvpeswere detectcdfrom
a total of 36 individuals.indicatinga high level
of diversitywithin this population.Thcsetindings ale in generalagreementwith the resultsre
ported fbr other clonal plant species. ln rheir
analysisof27 studies.
EllstrandandRoose( 1987)
repofiedthatthc percentage
ofmulticlonal popula
tions per study tendedto be high. with a mcan of
77% and a rangeof0 100%. The resultsobtained
lbr bulbousbluegrassue clearlyat the high cnd of
ths range.EllstrandandRoose(1987)aisorcpofied
thal the averlrgenumberofgenotypesdetectcdper
populationwas 16.1. However'.
this valueis inflated becauseonc ol thesespeciespossessed
167
gcnotypesper population.andifthis \?lue is eliminatedfrorr their calculationthe averagenumberof
genotypesper populationis reducedto 10.8 The
numberof genolypesdetectedper populationfbr
bulbousbluegrassis similar to the valuereported
above:on average,eachpopulationpossessed
9.6
multilocusgenotypes(Trrble3).
The numberof multilocusgenotypes
thatbu1bousbluegrasspossesses
is remarkablyhigh tbr
an lntoduccd clonal species.Thcory predictsthat
the number of genotypesdctectedis positively
conclatedwith the numberof individualsanaJyzedper population.and the number of characters(loci) employed(Ellstrandrnd Roose1987,
Bayer 1990). The lar-senumbel of multilocus
genotypes(clones)detectedin this studynay be
due to the tact that \\,e analyzcd,on average.26
individualsper population.and scoredvaliabililv in thesepopulationsusingthe lesultsof nine
polymorphicloci. A slightlyhighernumberof
chalacterswere employed for the identit-rcation
of clonesin the studicssummarized
by Ellstrand
andRoose( 1987):on average.I I characterswere
uscd.
In addition.suchhigh levelsofgeneticvariation lbr this speciesmay also be due to several
othel faclors:1) nrultipleiDlroductionol dil'1crent genotypesnav hare occurreddirecllv into
thcsclecations,and/or2) sone sexualreproduc
tion may havcoccurredwithin variouslocations
in iLsintroducedrangecventhoughall of the re
productivestructures
analyzedfuomthesepopulationswerc bulblets.
Conclusions
Bulbousbluegrasspossesses
a largeamountol'
geneticdivcrsitvdespitethe wideJyheld belicf
thatclonalspeciesdo nol possess
asmuchdiversity asscxualones. Thercfore,our resultsare in
generalagreement
with thesecondgroupof moclels
describedabove.and suggcstth t clonal spccies
arecapableof possessing
asmuchgeDeticdivcrsity assexualspccies(MaynardSmith 1971,Lynch
198,1.Ellstrandand Roose1987). Multiple infoduction eventsare a likely causeof thc high
levelof geneticdiversitywithin populationsand
the rcstricteddistributionof multilocusgcnotypes
p , , p u h l i o n .l.h c s c r e \ u l l . . i o i a
:lnrong
n sr,,$in!
body of geneticeyidencethat suggestsmultiple
introductionsofan alienspeciesmay bemorecommon thanpreviouslythoughl. In addition,asmall
amountofsexualrcproductionmay alsohtrvecontributcd to the high levcl of geneticdiversity ob
sencd ti)r this species.Finallv. it is intcrestingto
nolc thatthe role ofintroduction events,sexualre
production.and autopolyploidyin off-scttingthe
antlcipalcdlossofgenetic varirtion in thesepopulatlonscan only be fully resolvedby the analysis
ofpopulationsfiom thenativerange.As thispr(iect
expands,it shouldalsoincludethe analysisof Eul
asianpopulationsof bulbousbluegrass.
Acknowledgements
This studl'was conductedin partial fulfillment
of thc requirementslbr the undergraduateHon
ors Programat Boise StateUniversity by AYw.
We thank Jim Snrith, Loren Ca er. Regina
Rlche1,,n.
art,, a'"rn.andanln,'nrrrr,rr. rcriesr:r
l i r r c o n . t r u c t i r cc i r t n l n ( n l \o n t h e m i r n u s e r i p t :
JenniferOft tbr assistance
in the laboratory:and
K l r n S p e l m r nf o r r \ \ i \ r . l n c ei n t h e p r e p r r l l i o n
on tables. This projcct was llnded by a grant
from the FacultyRcsearchProgramat BoiseState
Unversityto SJN. and was aidcdby a Grant inAid of Researchfiorn Sigma Xi, the Scienlific
Research
Society,to AYW.
GeneticDilcrsity in BulbousBluegrass 2i9
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