Colony Isolation and Isozyme Variability of the Western Seep Fritillary, Speyeria Nokomis Apacheana (Nymphalidae), in the Western Great Basin

Great Basin Naturalist

Volume 54 Number 2 Article 1

4-29-1994

Colony isolation and isozyme variability of the western seep fritillary, Speyeria nokomis apacheana (Nymphalidae), in the western Great Basin

Hugh B. Britten Nevada Biodiversity Research Center, Department of Biology, University of Nevada, Reno

Peter F. Brussard Nevada Biodiversity Research Center, Department of Biology, University of Nevada, Reno

Dennis D. Murphy Nevada Biodiversity Research Center, Department of Biology, University of Nevada, Reno

George T. Austin Nevada State Museum and Historical Society, Las Vegas, Nevada

Follow this and additional works at: https://scholarsarchive.byu.edu/gbn

Recommended Citation Britten, Hugh B.; Brussard, Peter F.; Murphy, Dennis D.; and Austin, George T. (1994) "Colony isolation and isozyme variability of the western seep fritillary, Speyeria nokomis apacheana (Nymphalidae), in the western Great Basin," Great Basin Naturalist: Vol. 54 : No. 2 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol54/iss2/1

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. The Great Basin Naturalist PuBLISHED AT PROVO, UTAH, BY BRIGHAM YOUNG UNIVERSIn'

ISSN 0017-3614

VOLUME 54 30 APRIL 1994 No.2

Great Basin Naturalist 54(2), el994, pp. 97-105

COLONY ISOLATION AND ISOZYME VARIABILITY OF THE WESTERN SEEP FRITILLARY, SPEYERlA NOKOMIS APACHEANA (NYMPHALIDAE), IN THE WESTERN GREAT BASIN

Hugh B. Brittenl, Peter F. Brussard l , Dennis D. Murphy!, and George T. Austin2

ABSTRACT.-Thirteen Speyeria nokomis apacheana (Edwards) (Nymphalidae) populations from the western Creat Basin were assayed for isozyme variability using starch-gel electrophoresis. Eight of the 25 presumptive isozyme loci analyzed were found to be polymorphic. Collections made in 1991 and 19H2 allowed for between-year comparisons of heterozygosit)' and the estimation of effective population size for five of the sampled populations. Speyeria nokomis apacheana populations exhibit lower mean heterozygosity levels than other nymphalids. This may be attributed to genetic drift in apparently isolated populations with small effective sizes.

Key words: Lepidoptera, protein electrophoresis, population structure, hel-erozygosity, Great Basin, gene flow.

The western seep fritillary, Speyeria numbers ofpopulations. In this way extirpated nokomis apacheana (w. H. Edwards) (Nymph populations are recolonized, and declining alidae), is confined to mesic areas in the Great populations are genetically and demographi Basin where botb its larval foodplant, Viola cally augmented. Protein electrophoresis is a nephrophylla (Greene) (Violaceae), and the most useful tool for assessing population structure important adult nectar source, Onium (Mill.) and levels ofgenetic variability in species with (Asteraceae), co-occur. Adults ofthe single brood this type ofdistribution (e.g., Vrijenhoek et al. are present from late July through mid-Sep 1985, Waller et al. 1987, Dinerstein and tember and are rarely observed far from McCracken 1990). The two goals of this study colony sites. Population sizes are variable. were to ascertain population structure of Some colonies contain many hundreds ofindi Speyeria nokomis apacheana in the western viduals, while others can be quite small with Great Basin and to estimate levels of isozyme fewer than 10 adults obselVed over several days. variability \vithin its populations. Small, isolated populations theoretically are exposed to a number of demographic, environ MATERLALS A. D METHODS mental. and genetic threats to their persis tence (Gilpin and Soule 1986, Shaffer 1987, Speyeria nokomis apacheana adults were Boyce 1992). Long-term persistence of such collected from 10 sites in Nevada and eastern populations usuaUy requires dispersal among California in late August and September 1991

'Nevada Biodiversity Rese;m:h Center. Deporhocnt dBiolngy, University of Nevada-Reno, Reno. NC"lOda 89557. 2Nevllda SUite MIl$euni ~nd Historical Society. iOOTwin Lakes Drive. Las Vegas, NeY3tLi S9107.

97 98 GREAT BASIN NATURALIST [Volume 54

Seem Pass 0 Ruby Valley 0

Reno Reno o • Reese River * * o .. Kingston Canyon

• Sweetwater NOM* • Nye Canyon * CA Route 108. • Sweetwater South *, Devil's Gale

Round Valley.

Fig. L Map of the western Creat Basin with SpelJerla nokomis a:pachean.a collection sites denoted with closed circles (e). Sites sampled in 1991 and 1992 are indicated by •. and from 8 sites in late summer 1992 (Fig. 1). designated as "D," and progressively later let One or two collectors sampled each popula ters in the alphahet were assigned to still tion, and collecting efforts required 1-3 h per slower allozymes. site. Captured individuals were frozen in liquid Data from each year of sampling were nitrogen for transport and were subsequently analyzed separately. Estimates of polymor stored in an ultra-cold freezer at -80'C. phism level and heterozygosity and lests for Allozyme variation was assayed at 25 pre conformance to Hardy-Weinberg expectations sumptive loci (Table 1); general methods and were made using BIOSYS-l (Swofford and procedures followed Brossard et a1. (1985). Selander 1981). AX2 test for heterogeneity Genotype frequencies were obtained by (Sokal and Rohlf 1981) was used to lest the direct count from phenotypes observed on the significance of allele frequency differences gels. The most commou electromorph between populations at all polymorphic loci. (aJlozyme) at each locus was designated as FIXation indices (F-statistics) were estimated 'C," with relatively faster migrating allozymes for a hierarchy with three levels:total sample, scored as "B." Still faster migrating allozymes regional samples, and individual populations. were scored as 'K alleles. Likewise, allozymes Regions were delineated as (1) western, that migrated slower than the ·C· alleles were including nine sites in eastern California and 1994] WESTERN SEEP FRITILLARY COLONY ISOLATION 99

TABLE J. Enzymes assayed and buffer systems used in tht: protein electrophoretic analysis of Speyeria nukomis apacheana populations in the Great Basin.

Enzyme commission Locus Enzyme number BuffeT AAT-I,2,3 Aspartate aminotransferase 2.6.1.1 R' AK Adenylatc kinase 2.7.4.3 4" DlA NADH diaphorase 1.8.1.1 R GP-I,2.3 General (unidentified) protein C' CPl-l,2 Glucosephm..phate isomerase 5.3.1.9 4 G6PDH Glucose-6-phospbate dehydrogenase 1.1.1.19 4 HBDH Hydroxybuteric dehydrogenase 1.1.1.30 R IDDH [...iditol dehydrogenase 1.1.1.L4 R IDH-I,2 Isocilmte dehydrogenase 1.1.1.42 C MDH-l,2 NAD Malate dehydrogenase 1.1.1.37 4 MDHP NADP Malate dehydrogenase 1.1.1.10 C MPI Mannosephosphate isomerase 5.3.1.8 R PEP-A Peptidase (glycyl-leucinc) 3.4.-.- R PEP-E-I,2 Aminopeptidase (cytosol) 3.4.11.1 4 PGD Phosphogluconate dehydrogenase 1.1.1.43 C PGM Phosphoglucomutase 5.4.2.2 R SOD Superoxide dismutase 1.15.1.1 C

·Fmm R,dgt-....'ll.)' et al. (J970). bFmm Selasodcr ef;ll. (1971). CEloctrotRlino-pO"O()y1).morpholine; diluted 1:10 for gel buffer ((.1aytoll am! Tretiak 1972). western Nevada; (2) central, including Reese RESULTS River and Kingston Canyon sites; and (3) east Allele Frequencies and ern, including Secret Pass and Ruby Valley Genetic Variability sites (Fig. 1). Because F-statistics are hierar chical "inbreeding coefficients" (Hartl and Six of the 25 presumptive allozyme loci Clark 1989), they can be used to compare assayed were polymorphic in at least one of directly relative levels of gene flow among the populations sampled in 1991 (Table 2), and populations within regions and among popula all populations conformed to Hardy-Weinberg tions within the total sample. The simultane expectations at these loci. The 10 sampled ous test procedure (Sokal and Rohlf 1981) was populations were fixed for the same alleles at used to test for homogeueity of genotype fre all other loci analyzed. Mean observed het quencies among samples in the western erozygosity estimates ranged from 0.014 in the region to provide further insight into popula Secret Pass population to 0.042 for the Nye tion structure along Ihe eastern slope of the Canyon population (Table 2). Sierra Nevada. The genetically e/Tective num Seven of the 25 presumptive alIozyme loci ber of migrants per generation (Nm) within assayed in the 1992 samples were polymor homogeneous groups of populations was esti phic (Table 2), and all these samples con mated from the F-statistics following Slatkin formed to Hardy-Weinberg expectations at all (1987). Samples from sites collected in both polymorphic loci. As in 1991, all populations years were pooled for the calculation ofgenet were fixed for the same alleles at the ic dislances. The UPGMA clustering algo monomorphic loci. Mean observed heterozy rithm was used to derive a phenogram based gosity estimates ranged from 0.020 in the ye on genetic distances. Canyon population to 0.044 in the Sweetwater Genetically e/Tective population sizes (N:s) North population (Table 2). were calculated for populations sampled in both 1991 and 1992 using the methods of Nei Geographical Structure and Tajima (1981) and Pollack (1983). These Among Colonies methods calculate standardized variances in Sample sizes for 1991 and 1992 collection allele frequency change at polymorphic loci efforls are given in Table 2. Five sites were sampled at two or more difTerenl times. Tbese repeat-sampled in 1992 (Sweelwater North and variances provide an estimate of genetic drift South) Nye Canyon, Reese River, and Kingston which, in tum, is inversely related to Ne. Canyon), and yearly allele frequencies for 100 GREAT BASIN NATURAUST [Volume 54

TABLE 2. Sample sizes and allele frequencies at polymorphic loci assayed in Speyerla nokomis apocheana populations sampled in 1991 and 1992 with percentpolymorphic loci (P) and direct count mean heterozygosity estimates (H).

Western Central Eastern Sample site" SWN SWS DC Ne el08 ML se Rve LV RR Ke RV SP Sample size (1991) 21 42 18 20 10 20 0 0 0 58 34 17 14 Locu, Allele

AAT-2 B 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.25 e 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.75

CPI-I e 1.00 1.00 0.94 1.00 1.00 1.00 1.00 1.00 1.00 1.00 D 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00

CPI-2 B 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 C 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.68 1.00

MPI e 0.62 0.88 0.94 0.62 1.00 0.97 1.00 1.00 1.00 1.00 D 0.38 0.12 0.06 0.38 0.00 0.03 0.00 0.00 0.00 0.00

PCM B 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 C 0.74 0.33 0..,7 0.60 0.45 0.32 0.81 0.26 0.32 1.00 D 0.26 0.65 0.53 OAO 0.55 0.68 0.19 0.14 0.68 0.00

SOD C 1.00 1.00 1.00 1.00 1.00 1.00 0.65 1.00 1.00 1.00 0 0.00 0.00 0.00 0.00 0.00 0.00 0.35 0.00 0.00 0.00

P 8 8 12 8 4 8 8 4 8 4 H 0.036 0.024 0.027 0.042 0.020 0.016 0.032 0.016 0.028 0.014

Sample size (1992) 37 32 0 10 0 0 48 80 13 33 31 0 0

Locu' Allele

CPI-I e 1.00 1.00 1.00 1.00 1.00 1.00 0.98 1.00 0 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00

GPI-2 B 0.00 0.08 0.00 0.00 0.00 0.00 0.00 0.00 e 1.00 0.92 1.00 1.00 1.00 1.00 . 1.00 1.00

MOH-l B 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 e 1.00 1.00 1.00 1.00 1.00 1.00 0.98 1.00

MPI C 0.62 0.84 0.75 0.83 0.99 1.00 1.00 1.00 0 0.27 0.04 0.05 0.17 O.oJ 0.00 0.00 0.00 E 0.11 0.12 0.20 0.00 0.00 0.00 0.00 0.00

PCO B 0.00 0.00 0.00 0.00 O.oJ 0.00 0.00 0.00 e 1.00 1.00 1.00 1.00 0.99 1.00 0.97 0.95 0 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.05

PCM B 0.00 0.11 0.00 0.00 0.08 0.12 0.00 0.00 e 0.69 0.33 0.90 0.56 0.28 0.58 0.98 0.35 0 0.31 0.56 0.10 0.44 0.64 0.30 0.02 0.65

SOD e 1.00 1.00 1.00 1.00 1.00 1.00 0.61 1.00 0 0.00 0.00 0.00 0.00 0.00 0.00 0.39 0.00

P S 8 8 8 12 4 20 8 H 0.044 0.032 0.020 0.034 0.023 0.022 0.021 0.022

~Slllllple sites: SWN - Sweetwatet" North, SWS Swcet.watel' South, DC • ~vi!'i GAte. NC '" Nye Canyoo, CIOS '" Cal Rt 108, ML '" Mono Lake, SC Scossa. Ranch, RVe '" Round Valley, CA. LV - Lee Vining. RR .. R~ Rr.w, KG "" XJnguoll Ca.n)"XI. BV - Ruby Va!lsy. SP '" Secret Pass. 1994] WESTERN SEEP FRITILLARY COLONY ISOLATION 101

TABLE 3. Unbiased genetic distances (Nei 1978) above diagonal and unbiased genetic identities (Nei 1978) below diagonal for 13 Great Basin populations ofSpeyeria nokomis apacheana sampled in 1991 and 1992.

Population SWS SWN DC NC C108 ML SC RVC LV RV SP RR KC Sweetwater South ***** 0.007 0.000 0.006 0.000 0.000 0.002 0.000 0.003 0.004 0.020 0.017 0.001 Sweetwater North 0.993 ***** 0.005 0.000 0.007 0.010 0.002 0.011 0.005 0.D15 0.011 0.012 0.011 Devil's Gate 1.000 0.995 ***** 0.004 0.000 0.000 0.000 0.001 0.001 0.005 0.014 0.012 0.001

Nye Canyon 0.994 1.000 0.996 ***** 0.006 0.008 0.001 0.009 0.004 0.013 0.009 0.010 0.010 CA Rt 108 1.000 0.993 LOaD 0.994 **"'** 0.000 0.001 0.000 0.001 0.004 0.014 0.012 0.000 Mono Lake 1.000 0.990 1.000 0.992 l.000 ***** 0.003 0.000 0.004 0.004 0.021 0.D18 0.000 Scossa Ranch 0.998 0.998 1.000 0.999 0.999 0.997 ***** 0.003 0.001 0.007 0.011 0.011 0.004 Round Valley 1.000 0.989 0.999 0.991 1.000 1.000 0.997 ***** 0.004 0.004 0.022 0.019 0.000

Lee Vining 0.997 0.995 0.999 0.996 0.999 0.996 0.999 0.996 **"'** 0.008 0.008 0.008 0.004

Ruby Valley 0.996 0.985 0.995 0.987 0.996 0.997 0.993 0.996 0.992 ***** 0.025 0.022 0.004

Secret Pass 0.981 0.989 0.987 0.991 0.986 0.979 0.989 0.979 0.992 0.975 ***** 0.008 0.022

Reese River 0.983 0.988 0.988 0.990 0.988 0.982 0.989 0.982 0.992 0.978 0.992 ***** 0.019

Kingston Canyon 0._ 0.989 0.999 0.990 1.000 1.000 0.996 1.000 0.996 0.996 0.978 0.981 ***** these populations were pooled to represent an Hierarchical F-statistics also pointed to fine intergenerational mean that can be used to scale population structuring within regions for calculate genetic distances among the sampled hoth years. For example, the 1991 within populations. A UPGMA phenogram hased on region fixation index was 0.227. Using the Ners (1978) unbiased genetic distances (Tahle relationship F = 1/(1 + 4Nm) (Slatkin 1987), 3) did not represent the geographical relation we arrive at a figure suggesting an average of ships of the assayed populations particularly only 0.851 individuals dispersed between well (Fig. 2). For example, Secret Pass, an east colonies within each region in 1991. ern population, clustered on the UPGMA The six 1991 western samples were sub phenogram most closely with Reese River, a jected to a simultaneous test procedure (Sokal central population. Similarly, Kingston and Rohlf 1981) to obtain further insight into Canyon, a central population, clustered among the geographic structures among them. AU a group of western populations in the populations were heterogeneous except two phenogram. Because of the nonconcordance groups. The first, consisting of California of the phenogram in Figure 2 with the geo Route 108, Devi!'s Gate, Mono Lake, and graphical dispersion of the populations (Fig. Sweetwater South, was found to he homoge 1), we undertook a more detailed analysis of neous with respect to allele frequencies across the genetic structure of the sampled popula two ofthe three (MPI and PGM) polymorphic tions. loci in the samples. The greatest linear dis tance between any pair of these populations is Genetic Structure Among approximately 46 km (Fig. 1). The mean F and Within Regions st among the four populations was 0.022. The Significant heterogeneity in allele frequen second homogeneous group consisted of Nye cies (X2 test, p < .05) at all polymorphic loci Canyon and Sweetwater North, two popula among all sampled populations in both years tions separated by 2 km of apparently suitable of sampling indicated substantial population hahitat (Fig. 1). The mean Fst estimate for structuring. When regions were considered these two populations was 0.010. independently, significant levels of hetero The simultaneous test procedure revealed geneity in allele frequencies were observed no homogeneous groups among the 1992 west among the populations within each region. ern populations. Nye Canyon and Sweetwater 102 GREAT BASIN NATURALIST [Volume 54

Similarity

.98 .99 1.00 Region ----+----+----+----+----+

I I Sweetwater South West I I I I Devil's gate West I I --- california Route 108 West I I I I Mono Lake West I I ---- Round Valley West ,I I I Kingston canyon Central I I - 1-- Scossa Ranch West II II ,- Lee Vining ------I West ----- RUby Valley East I Sweetwater North ------I West I I Nye Canyon West ------Secret Pass East 1------1 ------Reese River Central

----+----+----+----+----+ .98 .99 1.00

Fig. 2. UPGMA phenogram based on Nei's (1978) unbiased genetic identities for 13 Great Basin populations of Spey~ eria nokomis apacheana. Regional designations indicate that topology ofthe phenogram does not correspond to the geo" graphic arrangement ofthe populations. Cophenetic correlation coefficient is 0.873.

North formed a marginally heterogeneous large confidence intervals around these esti group (total X2 for two loci = 8.45, df = 3, mates (Table 4) result from the small number p = .04) with a mean F st estimate of 0.05 of alleles used in their estimation and the (Nm = 4.7; Slatkin 1987). small number of generations (n = 1) over which the study was conducted (Nei and Taji Estimates of Effective Population Size ma 1981, Pollack 1983, Waples 1989). Despite Five Speyeria nokomis apacheana popula these limitations, the estimates are consistent tions, Sweetwater North and South, Nye with the high degree of structuring observed Canyon, Reese River, and Kingston Canyon, and indicate that the Ne's of Speyel'ia nokomis provided large enough samples in 1991 and in the Great Basin are generally small. 1992 (Table 2) to allow estimation ofNe's using the methods ofNei and Tajima (1981) and Pol DISCUSSION lack (1983). Estimates ofNe derived from both methods for replicated samples are given in Mean population heterozygosity estimates Table 4. Estimates were smaller than the num for Speyeria nokomis apacheana are consis ber of individuals sampled at each site. The tently lower than heterozygosity in other 1994] WESTERN SEEP FRITILLARY COLONY ISOLATION 103

TABLE 4. Estimates of effective population sizes (Ne's) relative to genetic drift in small populations for five repeat-sampled Speyeda nokomis apacheana pop (Crow 1986, Hartl and Clark 1989). ulations collected in 1991 and 1992. Confidence intervals are in parentheses. Because genetic drift in small, isolated pop ulations can erode heterozygosity over num Estimates ofNe bers of generations (Hartl and Clark 1989), it Population Nei and Tajima Pollack is the most plausihle explanation for the (1981) (1983) observed low levels of isozyme variability in Sweetwater North 36 10 the Speyeria nokomis populations included in (4-=) (0-37) this study. Drift is most effective in eroding Sweetwater South 9 6 heterozygosity and causing loss ofneutral alle (2-=) (0-17) les when populations are small and isolated. Speyeria nokomis populations in the Great Nyc Canyon 2 1 Basin appear to meet both criteria. Although (0-=) (0-4) fairly large sample sizes were obtained at sev Reese River 4 3 eral sites, much smaller samples were taken at (1-=) (0-11) most sites with similar collecting efforts (Tahle 2). Sample size, therefore, is a rough indicator Kingston Canyon 73 70 of relative population size, and most popula (3-=) (0-1ll8) tions appeared to consist of far fewer than 100 individuals on the days they were sampled. Estimates of N (Tahle 4) corroborate the evi nymphalid butterflies. For example, Brussard e dence for small effective population sizes in et al. (1989) estimated a range of mean het this taxon. erozygosities of 0.17-0.26 among western Several authors (e.g., Frankel and Soule North American populations in a complex of 1981, Allendorf 1986, Hedrick and Miller semispecies within the variable species highly 1992) have stressed the importance of drift in Euphydryas chaleedona. Britten et al. (1993) the loss of selectively neutral alleles from pop estimated mean heterozygosities of 0.041 ulations suhjected to hottlenecks. Populations 0.127 in Canadian Boloria improba, and 0.031 with chronically small sizes may be consid for the closely related, endangered, and nar ered analogous to populations that have suf rowly endemic butterfly Boloria acrocnema fered a series of hottlenecks. In that light, (Britten et al. 1994); both values are near the larger Speyeria nokomis populations would be high range of estimates for those of Speyeria expected to retain a larger complement ofalle nokomis in the Great Basin (Table 2). In addi les over longer periods of time than would tion, Brittnacher et al. (1978) estimated that smaller ones. mean heterozygosity in a number of California Furthermore, allele frequencies are expect Speyeria species and subspecies ranged from ed to fluctuate less between generations when 0,141 in Speyeria coronis caron-is to 0.067 in Ne's are consistently large. This hypothesis is Speyeria atlantis. Brittnacher et al. (1978) esti partially testahle by comparing the results of mated a mean heterozygosity of 0.034 for our study with those of Brittnacher et al. Speyeria nokomis apacheana at Round Valley, (1978) for the Round Valley population. Britt a figure somewhat higher than our estimated nacher et al. (1978) collected 58 Speyeria heterozygosity for that population (0.023, nokomis from this colony in 1974 and 1975. A Table 2), but within the range of estimates single locus (PGM) was polymorphic with the made herein for other Speyeria nokomis following allele frequencies: 0.69 for apaeheana populations (Tahle 2). "PGM97," 0.23 for "PGMlOO," and 0.08 for A number of evolutionary forces could be "PGM103" (Brittnacher et al. 1978). Based on responsible for the apparent lack of heterozy relative migration rates of alleles within each gosity in the sampled Speyeria nokomis study, PGM97, PGMlOO, and PGMI03 are apach-eana populations. Selection against het assumed to be homologous with PGMD, erozygous individuals is theoretically capahle PGMC, and PGMB, respectively, ofthe present of reducing heterozygosity. There is, however, study. As shown in Table 2, allele frequencies little indication that selection acts frequently at the PGM locus have changed little in this on allozymes, Furthermore, selection is weak large colony over the 18 years intervening 104 GREAT BASIN NATURALIST [Volume 54 between the two studies. In contrast, the Reese ACKNOWLEDGMENTS River sample, with an estimated Ne of 3-4 (Table 4), experienced some rather large This work was supported by the Nevada changes in allele frequencies at several loci in Biodiversity Research Center. We wish to the short interval between the 1991 and 1992 thank two anonymous reviewers for their use geuerations (Table 2). ful comments on the manuscript. Dispersal among butterfly colonies is expected to ameliorate the erosive effects of LITERATURE CITED genetic drift in individual populations. Het erogeneity tests and F-statistics, however, sug ALLENDORF, F, W. 1986. Genetic chift and the loss ofalleles versus heterozygosity. Zoo Biology 5: 181-190. gest that Speyeria nokomis colonies are gener BOYCE, M. S. 1992. Population viability analysis. Annual ally isolated from each other and that even Review of Ecology and Systematics 23: 481-506. geographically proximate populations are like BRITTEN, H. B., P. F. BRUSSAHD, AND D. D. MURPHY. ly to be drifting independently. Even though 1994. The pending extinction of the Uncompahgre the 1991 data suggest that two sets of popula fritillary butterfly. Conservation Biology: In press. BRIITNACHER, J. G., S. R. SIMS, AND F. J. AYALA. 1978. tions were homogeneous and that there was Genetic differentiation between species ofthe genus suhstantial gene flow among them (Slatkin Speyeria (Lepidoptera: Nymphalidae). Evolution 32: 1987), sample sizes from these populations 199-210. were necessarily small and the resultant BRUSSARD, P. F., J. F. BAUGHMAN, D. D. MURPHY, P. R. power of the G-test (Sokal and Rohlf 1981) to EHRLICH, AND J. WRIGHT. 1989. Complex popula tion differentiation in checkerspot butterflies detect heterogeneity among allele frequencies (Euphydryas spp.). Canadian Journal of Zoology 67: was low (mean power for painvise G-tests = 330-335. 0.046). Thus, the apparent homogeneity and BRUSSARD, P. F., P. R. EHRLICH, D. D. MUHPHY, B. A. implied high rate of gene flow among these WILCOX, AND J. WRIGHT. 1985. Genetic distances populations may not be real. Alternatively, dis and the taxonomy of checkerspot butterflies (Nymphalidae: Nymphalinae). Journal of the Kansas persal rates among colonies may change Entomological Society 58: 403--412. between years depending on weather or other CLAYTON, J. W., AND D. N. TRETIAK. 1972. Aminocitrate environmental conditions. In any case, buffers pH control in starch gel electrophoresis. colonies are not static; the number of individ Journal of Fisheries Research Board of Canada 29: 1169-1172. uals dispersing among colonies apparently CROW, J. F. 1986. Basic concepts in population, quantita changes from generation to generation. This tive, and evolutionary genetics. W. H. Freeman and situation probably reflects environmentally Co., New York. 213 pp. mediated fluctuations in population sizes and DINERSTEIN, E., AND G. F. MCCRACKEN. 1990. Endan one~homed lev~ resource availability. gered greater rhinoceros carry high els of genetic variation. Conservation Biology 4: The results of this study further eonfirm 417-422. that Speyeria nokomis populations are con FRANKEL, O. H., AND M. E. SOULE. 1981. Conservation fined to mesic seep, spring, and riparian areas and evolution. Cambridge University Press, Cam in the Great Basin. Such habitats are often bridge. 327 pp. GILPIN, M. E., AND M. E. SOULE. 1986. Minimum viable separated by tens of kilometers of unsuitable populations: the process of species extinction. Pages habitat in whieh individual butterflies have 13-34 in M. E. Soule, ed., Conservation biology: the never been observed. The isozyme data pre science of scarcity and diversity. Simmer Associates, sented' here indicate very low levels of gene Inc., Sunderland, Massachusetts. HARTL, D. L., AND A. G. CLAIIK. 1989. Prindples ofpopu flow among the sampled populations and sug lation genetics. Sinauer Associates, Inc., Sunderland, gest that these populations may have lost Massachusetts. 682 pp. genetic variability as a result of small effective HEDRICK, P. W., AND P. S. MILLER. 1992. Conservation sizes and genetic drift. Because a number of genetics: techniques and fundamentals. Ecological unique alleles were detected in several popu Applications 2: 30-46. NEI, M. 1978. Estimation of average heterozygosity and lations (Table 2), eonservation of individual genetic distance from a small number of individuals. colonies may he important to the evolutionary Genetics 89: 583-590. potential of this subspecies (Frankel and SouIe NEI, M., AND F. TAJIMA. 1981. Genetic drift and the esti 1981, Allendorf 1986). The apparent philo mation of effective population size. Genetics 98: 625-640. patrie nature of this butterfly results in geneti POLUCK, E. 1983. A new method for estimating the effec cally unique colonies whose habitat should be tive population size from allele frequency changes. preserved in order to achieve this goal. Genetics 104: 531-548. 1994] WESTERN SEEP FRITILLARY COLONY ISOLATION 105

RIDGEWAY, G. J., S. W. SHERBURNE, AND R. D. LEWIS. SWOFFORD, D. L., AND R. B. SELANDER. 1981. BIOSYS-1: 1970. Polymorphism in the esterases of the Atlantic a FORTRAN program for the comprehensive analy herring. Transactions of the American Fisheries sis of electrophoretiC data in populations genetics Society 99: 147-151. and evolution. Journal ofHeredity 72: 281-283. SELANDER, R. K., M. H. SMITH, S. Y. YANG, W. E. JOHN VRIJENHOEK, R. C., M. E. DOUGLAS, AND G. K. MEFFE. SON, AND J. B. GENTRY, 1971. Biochemical polymor 1985. Conservation genetics ofendangered fish pop phism and systematics in the genus Peromyscus. I. ulations in Arizona. Science 229; 400-402. Variation in the old-field mouse PeromysCU8 poliono WALLER, D. M., D. M. O'MALLEY, AND S. C. GAWLER. tus. Studies in Genetics VI. University ofTexas Pub 1987. Genetic variation in the extreme endemic lication 7103: 49-90. Pedicularis furbishiae (Scrophulariaceae). Conserva SHAFFER, M. 1987. Minimum viable populations: coping tion Biology 1: 335-340. with uncertainty. Pages 69-86 in M. E. SouIe, ed., WAPLES, R. 1989. A generalized approach for estimating Viable populations for conservation. Cambridge effective population size from temporal changes in University Press, Cambridge. allele frequency. Genetics 121: 379-391. SLATKIN, M. 1987. Gene £low and the geographic struc ture ofnatural populations. Science 236: 787-792. SOKAL, R. R., AND F. J, ROHLF. 1981. Biometry: the prin Received 24 August 1993 ciples and practice ofstatistics in biological research. Accepted 29 September 1993 W. H. Freeman and Co., San Francisco. 805 pp.