Biological Journal of the Linnean Society (1992), 47: 249-260. With 2 figures
Philopatry and genetic differentation in the
Aphelocoma jays (Corvidae)
A. TOWNSEND PETERSON
Committee on Evolutionary Biology, The University of Chicago, Chicago, Illinois 60637,
U.S.A.*
Received I 1 December 1990, acceptedfor Publication 6 March 1991
The effects of philopatry on levels of genetic differentiation were examined in the Aphelocoma jays
through comparisons of gray-breasted jays (A. ultramarina; highly philopatric) and scrub jays
( A . comlescm; dispersing). Gray-breasted jays breed cooperatively in groups of up to 25 individuals,
with individuals typically breeding either on the natal territory or on adjacent territories. Western
North American scrub jays breed in non-cooperative pairs, with individuals typically dispersing at
least 0.5 km, and often much farther. Genetic differentiation among six populations in northern
Mexico and the south-western United States in each of the species was compared using starch-gel
electrophoresis of protein products of 29 presumptive genetic loci. Strong differences in levels of
genetic differentiation exist between the two species, both when measured using F-statistics and in
terms of the slope of the isolation by distance relationship. These results suggest that social systems
involving high degrees of philopatry may lead to considerably elevated rates of genetic
differentiation and speciation.
KEY WORDS:-Philopatry - cooperative breeding - genetic differentiation
coerulescms - Aphelocoma ultramarina - shifting balance theory.
CONTENTS
Introduction . . . . . . . . . . .
Social systems and philopatry in the Aphelocoma jays
Methods . . . . . . . . . . . .
Results . . . . . . . . . . . .
Discussion . . . . . . . . . . . .
Acknowledgements
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References
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Appendix . . . . . . . . . . . .
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INTRODUCTION
The consequences of philopatry for social behaviour have recently been a
subject of intense empirical attention (e.g. Brown, 1987; Stacey & Ligon, 1987).
The effects of philopatry on differentiation and speciation of natural
populations, however, have had little attention since the work of Wright (1938,
1978, 1982). Wright pointed out that gene frequencies in sets of subdivided
populations can respond more rapidly than those in non-subdivided populations
*Present address: Field Museum of Natural History, Roosevelt Road at Lake shore Drive, Chicago, Illinois
60605-2496 U.S.A.
249
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A. T. PETERSON
to evolutionary processes such as adaptation, genetic drift and interdemic
selection. Hence, empirical investigations of the effects of philopatry on
evolutionary processes are of considerable interest (Barrowclough, 1980;
Rockwell & Barrowclough, 1987).
A number of factors can be demonstrated to affect genetic neighbourhood size
(the area within which an individual’s parents can be considered to have been,
drawn randomly from a panmictic population; Wright, 1969), including
dispersal distance, sex ratio, population density and variance in reproductive
success (Wright, 1978). Theoretical treatments predict that highly philopatric
species should be more genetically subdivided than less philopatric species
(Wright, 1938, 1978; Hartl, 1980). Decreased dispersal distance reduces the
genetic neighbourhood size, leading to increasing genetic difference with
geographic distance. Wright ( 1938, 1978) describes details of this positive
relationship between genetic and geographic distances. Hence, even within a
continuous geographic range, philopatric species are expected to exhibit genetic
subdivision.
I n spite of the theoretical interest, the relationship of philopatry to
interpopulation differentiation in natural populations is poorly known.
Cheverud, Buettner-Janusch & Sade ( 1978) documented increased genetic
differentiation after social group fission on a very local scale in rhesus macaques
(Macaca mulatta). Similar studies of local differentiation owing to social
structuring have been conducted by Johnson & Brown (1980) and Chesser
( 1983) for gray-crowned babblers (Pomastostomus temporalis) and black-tailed
prairie dogs (Cynomys ludovicianus), respectively. To date, only one study has
tested for such a relationship across species: Lidicker & Patton (1987) compared
levels of philopatry and interpopulation differentiation in four species of rodents,
and found no relationship. Additional studies incorporating more taxa and
better controlling confounding factors are needed.
Because avian social systems are relatively well documented, comparisons
among bird taxa provide a promising opportunity for investigations of this sort.
Numerous populations of the three Aphelocoma jay species (Aves: Corvidae) that
have been subjects of demographic studies [e.g. scrub jays ( A . coerulescens):
Atwood, 1980a, b (Santa Cruz Island, California); Woolfenden & Fitzpatrick,
1984 (Florida); D. B. Burt, personal communication (central Texas); W.
Carmen, personal communication (central California); M. J. Elpers, personal
communication (southern California); B. Winternitz, personal communication
(central Colorado); and D. B. Burt & A. T. Peterson, unpublished (southern
Mexico); gray-breasted jays ( A . ultramarina); Brown, 1963 (Arizona)] indicate
contrasting social systems and levels of philopatry both within and between
species. Hence, the Aphelocoma jays provide an ideal situation to test for an effect
of philopatry on genetic differentiation.
I compared the genetic structure of gray-breasted jays and scrub jays across
their shared range in northern Mexico and the south-western United States to
test the hypothesis that extreme philopatry associated with the communal
breeding system of gray-breasted jays causes greater genetic subdivision than in
the non-cooperative scrub jays. Restricting the comparison geographically to the
area of overlap between the ranges of two sister species allows some degree of
control of geographic and historical factors that might otherwise obscure the
effects of philopatry on levels of genetic differentiation. The test is conservative
PHILOPATRY AND GENETIC DIFFERENTIATION
25 1
Figure 1. Distribution maps and sampling scheme for scrub jays (circles) and gray-breasted jays
(squares) in Mexico and the south-western United States. Sample locations for each of the two
species are numbered and sample location details are given in the Appendix.
because the range of scrub jays is highly fragmented and local in the region (i.e.
common in certain localities, but apparently absent in others with similar
habitats), whereas that of gray-breasted jays is continuous (Fig. 1; Pitelka, 1951;
Peterson & Vargas, in press); this difference should increase structuring in scrub
jays relative to that in gray-breasted jays.
Social systems and philopatry in the Aphelocoma j a y s
The two species of Aphelocoma jays treated in the present study exhibit a
variety of social behaviours in different parts of their ranges. Scrub jays live in
territorial, non-cooperative pairs throughout western North America south to
the vicinity of Mexico City, but the distinctive Florida and southern Mexican
populations (Oaxaca) live in cooperative, single-pair family groups of 2-8
individuals (Woolfenden & Fitzpatrick, 1984; D. B. Burt & A. T. Peterson,
unpublished). Gray-breasted jays are found in large, communally-breeding
groups throughout their range, although groups appear smaller at the far northeastern tip of their range (Strahl & Brown, 1987; Brown & Horvath, 1989).
These differences in social systems are associated with differences in dispersal
distances, Three studies of western North American scrub jays indicate relatively
252
A. T. PETERSON
large dispersal distances: scrub jays in central California had a modal dispersal
distance of less than 1 km, but several individuals were found to disperse much
longer distances (up to 56 km; W. Carmen, personal communication), which
strongly affects gene flow estimates (Moore & Dolbeer, 1989); scrub jays in
southern California all dispersed at least 0.5-1.0 km (M. J. Elpers, personal
communication); and scrub jays in central Texas move a t least 2 km before
breeding (D. B. Burt, personal communication). Taken together, these studies
suggest that a minimum dispersal distance for scrub jays in western North
America is probably between 0.5 and 1.0 km.
In sharp contrast to the western North American scrub jays, gray-breasted
jays in Arizona often breed very close to or within their natal territories (Brown
& Brown, 1984, 1990). The great majority of individuals either remain to breed
on the natal territory or move to adjacent territories (J. L. Brown, personal
communication). Although territory size is larger in gray-breasted jays than in
scrub jays (Brown & Brown, 1990), the actual distance dispersed is reduced in
gray-breasted jays. Hence, the Arizona populations of gray-breasted jays are
characterized by dispersal distances substantially shorter than those of scrub
jays.
I n this study, I focus on genetic differentiation in populations in the area of
overlap in geographic range between gray-breasted and scrub jays (Fig. 1)’ thus
controlling several geographic and historical factors that often confound such
comparisons. Although the only long-term demographic study of either species in
this region is that of Brown & Brown (1984, 1990), my own field observations
during 1986-1992 (Peterson, 1990; Peterson & Vargas, in press) indicate that
the social behaviour of these populations is similar to that of better-studied
populations elsewhere in the species’ ranges. Although no data on dispersal
distances exist for the populations of scrub jays in the region, cooperative and
non-cooperative populations of Aphelocoma jays appear quite uniform in their
dispersal characteristics in the populations for which information is available.
Hence, for the purposes of this paper, it is assumed that the cooperative and noncooperative populations of Aphelocoma jays in northern Mexico and the southwestern United States disperse distances similar to those of their better-studied
northern counterparts.
METHODS
As part of a large-scale study of genetic differentiation in the Aphelocoma jays, I
collected 107 gray-breasted and 129 scrub jays a t six sites each throughout their
shared range in northern Mexico and the south-western United States (Fig. 1,
Appendix), for averages of 17.8f5.7 S.D. and 22.6k2.7 S.D. individuals per
site, respectively. Subject to limitations imposed by permit restrictions and
logistics, collecting sites were placed ( 1 ) to cover the species’ ranges as evenly as
possible and (2) to represent patterns of morphological differentiation (Pitelka,
1951). Sample locations and numbers are given in the Appendix. Genetic data
on 16 additional scrub jay populations from throughout the species’ western
North American range are included in the calculations of rate of isolation by
distance; complete details are given in Peterson (1990). Tissue samples are
deposited in the Frozen Tissue Collection of the Field Museum of Natural
History, and voucher specimens (skins and skeletons) are deposited in the Field
PHILOPATRY AND GENETIC DIFFERENTIATION
253
Museum of Natural History and the Museo de Zoologia, Facultad de Ciencias,
Universidad Nacional Aut6noma de MCxico.
Equal portions of heart, muscle, and liver were homogenized in a 1 mM
disodium EDTA/100 mM Trizma Base/0.2 mM NAD, NADP and ATP buffer,
centrifuged for 20-45 min at 12 000 r.p.m., and the supernatants drawn into
capillary tubes for storage. Samples were electrophoresed for 4-10 h on 10-12%
starch gels, depending on the specific analysis desired. Gels were sliced
horizontally, and each slice stained using protein assays from Shaw & Prasad
(1970) and Harris & Hopkinson (1978).
Each sample was analysed for protein variation at 29 presumptive genetic loci,
including the following (enzyme number codes from Harris & Hopkinson, 1978):
ACON (4.2.1.3), ACP (3.1.3.2; erythrocytic acid phosphatase form), ADA
(3.5.4.4),ADH ( l . l . l . l ) , A K (2.7.4.3;2loci),CK (2.7.3.2;2loci),ES (3.1.1.1;2
loci), FH (4.2.1.2; 2 loci), GDA (3.5.4.3), GOT (2.6.1.1), GPD (1.1.1.8), GPI
(5.3.1.9), ICD (1.1.1.42), LDH (1.1.1.27; 2 loci), MDH (1.1.1.37; 2 loci), MPI
(5.3.1.8), PEP (3.4.11; Leu-Ala-two loci, Leu-aminopeptide-one locus), PGD
(1.1.1.44), PGM (2.7.5.1), SOD (1.15.1.1) and SORDH (1.1.1.14). To assure
correct assignment of homologies between gels, reference individuals were
included on each gel. Alleles in different populations were not considered
equivalent until found indistinguishable in at least one side-by-side comparison.
Homology assignments for each locus were rechecked under different buffer
conditions and/or at increased migration distances. Complete details of
laboratory procedures are given in Peterson (1990).
Allele frequencies were summarized by direct count. Heterozygosity (4and
its standard error were calculated by averaging the observed proportion of loci
heterozygous across individuals. Other measures of genetic variability used were
proportion of loci polymorphic and number of alleles per polymorphic locus
within populations.
Populations were tested for departure from Hardy-Weinberg expectations by
calculating expected heterozygosities as
where the first summation is over all loci and the second is over all alleles at the
ith locus, N is the number of loci examined, and xij is the frequency of the j t h
allele at the ith locus. Observed and expected numbers of heterozygotes were
then compared using a chi-square test, with degrees of freedom (d.f.) equal to
the number of alleles minus one summed over all loci.
Distribution of genetic variation within and between populations was assessed
using three forms of F-statistics (Wright, 1978): ‘Wright’s’, uncorrected and
corrected. F-Statistics and the genetic distance measure of Rogers (as modified
by Wright, 1978) were calculated over all variable loci using programs
developed by Scott M. Lanyon (unpublished). Significance of differences in Fs,s
between the species was evaluated using a jackknife manipulation (Lanyon,
1987), in which each population sample of each species was omitted sequentially
from analysis, and the resulting two sets of six estimates compared using a
Student’s t-test. Results based on Nei’s genetic distances (Nei, 1978) were
qualitatively identical to those reported here.
I first tested the statistical significance of the isolation by distance relationship
(i.e. correspondence between genetic and geographic distances) and then
254
A. T. PETERSON
described its form, as follows. Geographic distances were calculated from
latitude-longitude data using a great-circle approximation (Maling, 1989). This
measure was found to be accurate to within 1 km on a continental scale
compared with values calculated on the length of the geodesic (Fitzpatrick &
Modlin, 1986). Genetic and geographic distance matrices were compared using
a Mantel’s test from the NTSYS-pc package (Rohlf, 1988). The degree of
isolation by distance was estimated as the slope of the regression of genetic
distance (D)on geographic distance. T h e usual tests for equality of regression
parameters could not be employed because ( 1 ) neither genetic nor geographic
distances were normally distributed, and various transformations failed to
improve normality, and (2) sample sizes were inflated due to non-independence
of points in the matrices. I therefore used a bootstrap manipulation, resampling
the data for each species 100 times with replacement and compared the resulting
distributions of parameter estimates using a Mann-Whitney U-test.
RESULTS
Genetic variation within scrub jay populations is generally greater than
variation within gray-breasted j a y populations (Table 1). Based on a
conservative, non-parametric comparison of population means, scrub jays have
significantly higher levels of heterozygosity than gray-breasted jays (Table 1,
Wilcoxon signed-ranks test, P < 0.05). Deviations from Hardy-Weinberg
expectations do not differ signficantly from zero in any population ( P > 0.05).
Geographic variation in allele frequencies in scrub jay populations in this
study is relatively minor, the most extreme example being ES1, in which one
allele varies in frequency between 0.45 and 0.90 (complete allele-frequency table
given in Peterson, 1990). Allele-frequency variation in gray-breasted jays,
however, is much more pronounced. For example, an allele at the ADA locus
varies in frequency from 0.27 in the east to 1.00 in the north-west; one of the
alleles at the GDA locus is fixed in central-southern populations, but the other
allele is fixed in the north-west, and present a t 0.46 frequency in the north-east.
Variation within the continuous gray-breasted jay populations of the Sierra
Madre Occidental (Pitelka, 1951) is similarly strong, with an allele at the GDA
locus ranging in frequency from 1.00 in the northwest to 0.35 in the southwest.
F-Statistics are strikingly different in the two species (Table. 2). In all
calculations of F-statistics, values for gray-breasted jays (Wright’s F,, = 0.2502)
are more than three times greater than those for scrub jays (Wright’s F,, =
0.0558). [These calculations are based on 14 variable loci in scrub jays and 12
variable loci in gray-breasted jays; although some loci are variable in one species
TABLE1 . Levels of within-population variation in scrub jays and gray-breasted jays in six
populations each, reported as meanf S.E. (range)
Species
Heterozygosity
Percent of polymorphic
Number of alleles
Scrub jay
0.048&0.016
(0.032-0.073)
0.195 0.083
(0.103-0.344)
2.725 f0.312
(2.5-3.3)
Gray-breasted jay
0.035 & 0.017
(0.006-0.052)
0.138f0.062
(0.034-0.207)
2.31 7 f0.402
(2.0-3.0)
255
PHILOPATRY AND GENETIC DIFFERENTIATION
TABLE2. F-Statistics describing the distribution of genetic
variation in six populations each of scrub jays and gray-breasted
jays
F-Statistic
Wright's F,,
Corrected F,,
Uncorrected F,,
Scrub jay
Gray-breasted jay
0.0558
0.0265 f 0.01 10
0.0474f0.0110
0.2502
0.0849f 0.0442
0.1082f0.0439
and not in the other, strong differences in levels of subdivision are evident at a
number of loci (e.g. ADA, GPD) variable in both species. Calculations based
only on the loci polymorphic in both species indicate that the difference between
species remains strong.] That the higher levels of differentiation in gray-breasted
jays do not simply result from a more subdivided geographic range (Sierra
Madre Occidental vs Sierra Madre Oriental; Pitelka, 1951) is indicated by a
high value of F,, within the continuous populations of the Sierra Madre
Occidental (Wright's F,, = 0.1705), as well as marked geographic differences in
frequencies of a number of alleles (Peterson, 1990). Several individual loci show
high Fs,s in gray-breasted jays, including G D A (Fst= 0.5401), A D A (Fst=
0.1599), and GPD (F,, = 0.1339). A jacknife manipulation indicates that graybreasted jays show significantly higher Fs,s than scrub jays (Student's t-test,
t = 8.686, d.f. = 10, P < 0.0001).
A Mantel's test indicates that genetic and geographic distance matrices for the
six populations of gray-breasted jays are marginally significantly more similar
Gray-breasted jays
(0)
0
0
.
0
1000
2000
3000
4000
Geographic distance (km)
Figure 2. Regressions of modified Roger's genetic distances on geographical distanres in scrub jays
and gray-breasted jays.
256
A. T. PETERSON
than expected by chance (P= 0.052). I n scrub jays, no significant relationship is
found for the six populations under study (P> 0.300). The points from the six
scrub j a y populations considered here form a generally positive relationship, but
it appears that the range of genetic distances is insufficient to allow detection of
significance. However, among 22 scrub jay populations throughout the species’
mainland range sampled as part of a larger study of scrub jay genetics, a highly
significant result was obtained (P< 0.001; Peterson, 1990); further analyses of
isolation by distance in scrub jays are hence based on this expanded set of
populations.
Based on the relationships between genetic differentiation and geographic
distance, the slope of the isolation by distance relationship is estimated as
D.km-’ in scrub jays
5.42 x lov5D .km-’ in gray-breasted jays, and 1.87 x
(Fig. 2). The two estimates are significantly different based on a bootstrap
manipulation (P< 0.0005). The higher slope in gray-breasted jays indicates that
genetic differentiation accumulates about three times more rapidly with distance
in gray-breasted jays than in scrub jays.
DISCUSSION
Variation in social systems and demographic parameters is well documented
for a number of vertebrate species (e.g. Greenwood & Harvey, 1982; Smuts
et al., 1986; Brown, 1987; Chepko-Sade & Halpin, 1987). Rodent social systems,
for example, range from individual, separate-sex territories to complex territorial
social groups (Lidicker & Patton, 1987). I n birds, social systems range from pairbreeding, territorial populations, to highly social group-living populations
(Brown, 1987). Variation in demographic features is hence a common feature of
vertebrate taxa, leading to the question of whether long-term evolutionary
consequences derive specifically from this variation.
To date, only two studies have explored this question. Lidicker & Patton
(1987) compared dispersal distances and genetic differentiation in four species of
rodents. Although the taxa considered spanned the range of rodent social
systems, levels of genetic differentiation were not strikingly variable, and no
significant relationship was found. Bush et al. (1977) compared rates of
speciation and chromosomal evolution in 225 non-avian vertebrate genera. On
finding a strong positive relationship between rates of speciation and
chromosomal evolution, they presented anecdotal evidence for a causal
relationship with social structure. Hence, previous studies have not
convincingly demonstrated the predicted relationship between philopatry and
levels of differentiation.
The results of this study indicate that gray-breasted jays are more genetically
structured than scrub jays. Scrub jays in northern Mexico show relatively little
among-population differentiation (not true elsewhere in the species’ range;
Peterson, 1990) and hence resemble the majority of temperate zone species
studied to date. T o the extent that confounding factors have been controlled,
differences in levels of philopatry thus appear to affect levels of genetic
differentiation in these two species. The test is conservative given that two factors
(range fragmentation and reduced vagility) should lead to greater structuring in
scrub jays. A third factor, geographic diversity, should further increase
heterogeneity in scrub jays, as the north-eastermost and north-westernmost
PHILOPATRY AND GENETIC DIFFERENTIATION
257
samples of that species are each about 200 km farther removed from populations
to the south than are the corresponding gray-breasted jay samples. Moreover,
the result that gray-breasted jays, which show low levels of within-population
variation, are much more genetically structured than scrub jays is surprising
given that lower levels of heterozygosity might be expected to retard population
differentiation for lack of variation to be assorted among populations.
Few alternative hypotheses yield the prediction of greater genetic structuring
in gray-breasted jays. One potential explanation is rejected as implausible: scrub
jays could be more recent invaders in northern Mexico than gray-breasted jays.
At least on a coarse scale, this scenario improbable because well-marked, near
species-level differentiates of scrub jays are found both north and south of the
region in question, indicating long presence in the area treated in this study
(Pitelka, 1951; Peterson, 1990). Furthermore, even if gray-breasted jays have a
longer history, they show greater differentiation among populations even within
continuous habitat.
A second hypothesis warrants more consideration. Because gray-breasted jays
inhabit higher-altitude habitats than scrub jays, they may have been subjected
to periods of subdivision during Pleistocene climatic fluctuations. This
explanation appears untenable because the distribution is currently nearly
continuous, and no available palaeoclimatic evidence indicates that life zones
during the Pleistocene were significantly higher than current levels (Ericson,
Ewing & Wollin, 1964; Betancourt, 1984; Van Devender, Thompson &
Betancourt, 1987). Hence, the difference in philopatry is the only factor
predicting greater genetic subdivision in gray-breasted jays than in scrub jays.
The results of this study constitute a more controlled test than previous
investigations of this sort. The two species compared are sister species (Peterson,
1990), have an almost identical distribution in the region under study and
appear to have similar histories in the region. Perhaps controlling these
potentially confounding factors allowed the effects of social structure to be
detected, whereas they were obscured in other studies.
The results of this study, as well as a number of theoretical treatments (e.g.
Wright, 1978), lead to an interesting prediction: long-term rates of
differentiation and speciation should be higher in lineages having social systems
involving high degrees of philopatry. This hypothesis is testable in within-species
comparisons of populations differing in demographic parameters and in higherlevel comparisons of social and non-social sister lineages.
These results also lead to speculations about how well these species fit into the
scenario for Wright’s (1965,1978) Shifting Balance Theory of evolution. Wright
(1965) describes the process as consisting of three stages: (1) “the differentiation
of innumerable small local populations by more or less random processes that
lead, here and there, to the crossing of shallow saddles in the surface of selective
values.. .,; (2) “the occupation of the higher peaks by local mass selection and
[this stage] involves much greater changes of gene frequency than phase 1”; and
(3) “the diffusion of the significant aspects of the genetic constitution of these
successful populations throughout the species” by interdemic selection.
The results of this study demonstrate that genetic differentiation is much
stronger in a species with populations that are behaviourally subdivided than in
a species lacking such subdivision. This pattern is consistent with phase 1
(subdivision) and possibly phase 2 (differentiation) of Wright’s theory. Whether
258
A. T . PETERSON
or not certain populations have characters lending a selective advantage over
other populations is as yet unknown.
In this regard, however, the difference in beak-colour maturation rates
between the eastern populations and the western and southern populations of
gray-breasted jays (Pitelka, 1951; Peterson, 1991a) becomes very interesting.
Western and southern populations retain the ‘juvenile’ yellow beak colouration
often until 1.5 years of age, whereas the beak colour of the eastern populations
matures to black within a few months. A zone of intergradation between the two
ontogenetic types is found in the Mexican states of Guanajuato, Aguscalientes,
Jalisco and Zacatecas (Pitelka, 1951; Peterson, 1991a). Monitoring the position
of this transition zone may provide evidence that an apparently adaptive
character (delayed beak-colour maturation; Peterson, 1991a ) is spreading
among the subdivided populations of the species.
ACKNOWLEDGEMENTS
Many people have provided invaluable assistance to me during these studies;
to all of them, I give my heartfelt thanks. Scott Lanyon generously provided
instruction, advice and access to the Biochemical Systematics Laboratory at the
Field Museum of Natural History. Special thanks go to my advisors Stuart
Altmann and John Fitzpatrick for interest and advice; to Amy Peterson; and to
Frank Pitelka for interest and advice throughout the study. Thanks to Brent
Burt, John Fitzpatrick, Scott Lanyon, Robert Zink and Steve Schuster for
critical reviews of the manuscript; to the governments of Mexico and the states of
Arizona and Texas for providing collecting permits; and to Adolfo Navarro and
Patricia Escalante for making my field studies in Mexico possible. My research
was supported by grants from the National Science Foundation Dissertation
Improvement Grant program (BSR-8700850), the National Geographic Society,
the Chapman Fund of the American Museum of Natural History, Sigma Xi, the
Field Museum of Natural History and the University of Chicago.
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APPENDIX
Details of sample locations
Gray-breastedjays: (1) Mtxico, Sierra El Carmen, 4 km S, 3 km W Madero El Carmen, 28"56", 102"36'W,
22 inds.; (2) Hidalgo, 5 km N, 2 km E Jacala, 21"3'N, 99"W, 20 inds.; (3) San Luis Potosi, Sierra de Bledos,
5 km N, 5 km E Bledos, 21"52'N, 101"9'W, 22 inds.; (4) Jalisco, Sierra de Bolaiios, 8 km W Villa Guerrero,
21"59", 103"40'W, 7 inds.; (5) Zacatecas, 9 km N, 6 km W Valparaiso, 22"51'N, 103"38W, 20 inds.;
(6) U.S.A., Arizona, Santa Cruz Co., 5 km Petia BIanca Lake, 31"25'N, 111"8W, 16 inds.
Scrubjays: ( 1 ) U.S.A., Texas, Jeff Davis Co., 25 km W, 10 km N Ft. Davis, 30"42'N, 104"8'W,26 individuals;
(2) Mexico, Coahuila, El Diarnante Pass, 12 km E, 6 km S Saltillo, 25"22", 1OO052'W, 21 inds.; (3) San Luis
Potosi, 2 km N, 3 km W Bledos and Sierra de Bledos, 5 km N, 5 km E Bledos 21"52'N, 101"9'W, 22 inds.; (4)
Jalisco, 10 km E Lagos de Moreno, and Rancho Santa Rita, 9 km N Lagos de Moreno, 21"27'N, 101"55'W, 20
inds.; (5) Durango, 3 km N, 2 krn E Villa Ocampo, 26"28'N, 105"29'W, 21 inds.; and (6) U.S.A., Arizona,
Coconino Co., 9.7 km E Drake and Yavapai Go., 11.3 km E and 12.9 km ESE Drake, 35"N, 112"15'W, 26 inds.