Biochemical Genetics, VoL 16, Nos. 7/8, 1978
Heterozygosity in Yellowstone Park Elk, Cervus canadensis D. G. Cameron 1 and E. R. Vyse 1 Received 7 Sept. t977--Fina118 Jan. 1978
Protein products of 24 loci from the genomes of Yellowstone Park elk were analyzed by electrophoresis. Heterozygosity was detected in only one system, making elk much less polymorphic than eastern whitetailed deer. Data for several other large mammals are compared with those for elk and reveal similarly low levels of isozymic variation. The data are consistent with the fine-grained niche theory but difficult to reconcile with bottlenecks and genetie
drift. KEY WORDS: isozymes; mammals; heterozygosity; polymorphism; elk.
INTRODUCTION Surveys of isozymes in natural populations of sexually reproducing animals have usually revealed large reservoirs of genetic variability (Selander, 1976; Powell, 1975). Small vertebrates frequently contain less variability than insects or marine invertebrates. In comparison, little is known about the genetic structure of large mammals, particulai'ly western North American big game ungulate species. Although their total population numbers are large, the harvest of big game in North America is attained by public hunting over extensive areas, making the collection of fresh tissue samples difficult. At irregular intervals, however, climatic conditions force elk to emigrate out of Yellowstone National Park in Wyoming, presenting an unusual opportunity to collect specimens. In 1973-1975 intensive elk hunts were allowed in the Gallatin River Canyon west of the Park, and in January 1976 a special hunt 1 Department of Biology, Montana State University, Bozeman, Montana, 59717. 651 0006-2928/78/0800.0651505.00[0©1978PlenumPublishingCorporation
652
Cameron and Vyse
took place near Gardner, Montana, north of the Park, allowing access to different segments of the Yellowstone herd. We report the results of electrophoretic studies conducted on tissues collected from entrails left by hunters during these hunts and also from tissues obtained from a Yellowstone-derived herd inhabiting the Big Belt Mountains near Cascade, Montana. The level of heterozygosity found in Cervus canadensis will be compared with available genetic data on other large mammals. MATERIALS AND METHODS Samples were collected on the day of the kill, either while the hunters were dressing their game or as soon after as possible. Usually entrails were left on frozen ground or snow, which helped to minimize enzyme degradation. When possible, samples of heart, muscle, liver, kidney, and blood were taken. Blood samples were frequently obtainable from the heart. Tissue samples were frozen immediately on dry ice and stored at - 50 C. Blood samples were kept on ice and later centrifuged to separate cells and serum before storing at - 50 C. The number of specimens analyzed differed for each protein system but varied between 25 and 200. Both sexes and all age groups were included. Horizontal starch gel electrophoresis was performed using the methods reported by Selander et al. (1971) and Manlove et al. (1976). Direct comparisons between white-tailed deer and elk were made during a working visit to the Savannah River Ecology lab by D. G. C. The proteins analyzed by electrophoresis and the abbreviations used are as follows: lactate dehydrogenase, LDH (1.1.1.27); esterase, Est (3.1.1.1); phosphoglucomutase, PGM (2.7.5.1); malate dehydrogenase, M D H (1.1.1.37); phosphoglucoisomerase, PGI (5.3.1.9); glutamate-oxaloacetate transaminase, GOT (2.6.1.1); ph0sphogluconate dehydrogenase, 6PGD (1.1.1.44); glucose-6-phosphate dehydrogenase, G6PD (1.1.1.49); glucose dehydrogenase, G D H (1.1.1.47); sorbitol dehydrogenase, SDH (1.1.1.14); isocitrate dehydrogenase, IDH (1.1.1.42); superoxide dismutase, SOD (1.15.1.1); malic enzyme, ME (1.1.1.40); acid phosphatase, AP (3.1.3.2); albumin, Alb; transferrin, Trf; hemoglobin, Hb. RESULTS Elk genetic variation will be compared with other large mammals in two ways. In Table I, the 24 presumptive genetic loci studied are compared with homologous loci in all other large mammals for which comparable data are available. By restricting the comparisons to homologous loci, the precision by which/~is estimated is decreased, particularly in elephant seals, but the method has merit because different genetic systems are suspected of having different intrinsic h
Heterozygosity in Yellowstone Park Elk
653
+1
+~
o
0
0
0 >
0
2
0
0
0
f~ 0 0
o
+~
+~
~
0
E Q
~ ~
E 0
I
+1
k-,
+t
Cameron and Vyse
654
Table I1. Heterozygosity and Polymorphic Loci in Large Mammals° Speciesb
Loci
Er
p
Reference
Elk Moose~ White-tailed deer Man Northern elephant seal Southern elephant seal Black beara
24 23
0.012+0.012 0.0006 + 0.0002
0.04 0.04
Ryman et al. (1977)
28 74
0.I0+_0.033 0.099 + 0.21
0.32 0.31
Manlove et aL (1976) Nei and Roychoudhury (1974b)
24
0.0
0.0
Bonnell and Selander (1974)
18 16
0.03 _ 0.016 0.02 _+0.025
0.27 0.12
McDermid et at. (t972) Manlove et aL (1978)
a Data for all loci in the reference cited. b Genera and species in order: Cervus canadensis, Alees alces, Odocoileus virginianus, Homo sapiens, Mirounga angustirostris, M. leonina, Ursus americanus. Average of three populations, 2 years. aAverage of three populations, 16 loci.
values irrespective of the species in which they function (Selander, 1976). By these criteria elk appear to be comparatively monomorphic. Only one locus out of 24 is polymorphic (Table I). This locus was polymorphic in all samples and the allele frequencies did not differ between samples. Standard errors o f / t are large in all these studies, so one should be cautious in concluding that significant differences exist among the tabulated species, with the possible exception of eastern white-tailed deer which are highly polymorphic. In Table II the/7 and/~ values are presented on all loci published for large mammals (excluding domestic animals). The/-7 values calculated when all loci are used suggest that elk, moose, bear, and elephant seals fall into one group and that man and whitetail deer are more highly polymorphic. The proportions of polymorphic loci in elk, moose, and northern elephant seals are much lower than in the other species. DISCUSSION In a pioneer study on large mammals, Bonnell and Selander (1974) found no polymorphism in 24 presumptive loci in northern elephant seals. This monomorphy they attributed to a bottleneck effect brought about by the near extinction of the species in the mid-nineteenth century. Elk heterozygosity is not significantly different from that of northern elephant seals, but Yellowstone elk have not experienced a serious bottleneck. Houston (1974) estimates that the northern Yellowstone herd contained at least 4000 individuals and the
Heterozygosity in Yellowstone Park Elk
655
Gallatin herd 1000 individuals throughout the period when game animals were being decimated across western North America. The current herd sizes exceed 10,000 and 2000, respectively. Unfortunately, we cannot accurately estimate Are for these herds, but their effective population numbers are less than their census counts because of overlapping generations, harem breeding behavior, and population subdivision. Nevertheless, using conservative Ne/N ratios, the effective population numbers must have been several hundred or more at and since the nineteenthcentury bottleneck in the Yellowstone herds. Do the low levels of isozyme variation found in large mammals represent a special adaptive genetic strategy, or do they simply reflect stochastic interactions between neutral mutations and genetic drift? If the stochastic explanation is to hold and mutation rates in large mammals are not unusual, then genetic drift is strongly implicated (King and Jukes, 1969). Either the longterm Arewas low in large mammals or recent bottlenecks have rendered them genetically depauperate. Nei et al. (1975) have shown that bottlenecks can produce surprisingly little short term dimunition in heterozygosity. For example, a sample of only two individuals drawn from a randomly mating population should contain 75% of the heterozygosity found in the parent population, a sample of ten should contain 95%, and a sample of 100 should contain 99.95%. Nei's argument leads us to conclude that today's low levels of heterozygosity in northern elephant seals, moose, or elk probably were not generated by nineteenth-century bottlenecks but more likely by population subdivision or inbreeding of long duration if neutralist theory is applicable at all. /?values calculated using all of the loci available (Table II) are larger than those calculated in Table I. Variation does not appear to be randomly distributed among the loci amenable to analyses by electrophoreses, but polymorphic systems do not group conveniently by function (Gillespie and Kojima, 1968), substrate (Kojima et al., 1970), or quaternary structure (Ward, 1977). Unpublished data on polar bears, Thalarctos maritimus (Allendorf et al., 1978), suggest that this large mammal is also relatively monomorphic. All of these findings seem inconsistent with the neutral allele theory unless by some ecological constraint large mammals have small effective population sizes. Several niche or adaptational theories of population heterozygosity have been reviewed by Soule (1976) and Valentine (1976). We find little in the environmental amplitude or resource stability theories to explain low heterozygosity in large mammals. There is, however, consistency with Selander and Kaufman's (1973) prediction that low heterozygosity would be found in organisms experiencing fine-grained environmental variation because of their high mobility. There is even consistency in the different/? values between the highly
656
Cameron and Vyse
m o b i l e elk a n d m o r e s e d e n t a r y white-tailed deer. A m o r e c o m p r e h e n s i v e survey o f N o r t h A m e r i c a n C e r v i d a e c o u l d be revealing in this regard.
ACKNOWLEDGMENTS W e express o u r a p p r e c i a t i o n to the M o n t a n a State F i s h a n d G a m e for help in collecting samples, A s s o c i a t e d Universities o f O a k R i d g e Visiting F e l l o w P r o g r a m for travel s u p p o r t , a n d Dr. M. H. S m i t h a n d M. M a n l o v e for assistance at the S a v a n n a h R i v e r E c o l o g y L a b o r a t o r y .
REFERENCES
AUendorf, F. W., Christiansen, F. B., Eanes, W, F., and Frydenberg, O~(1978). Homozygosity in the polar bear. Science (submitted). Bonnell, M. L., and Selander, R. K. (1974). Elephant seals: Genetic variation and near extinction. Science 184:908. Gillespie, J. H., and Kojima, K. (1968). The degree of polymorphism in enzymes involved in energy production compared to that in nonspecific enzymes in two Drosophila ananassae populations. Proc. NatL Acad. Sci. 61:582. Houston, D. (1974). The northern Yellowstone elk. Parts I and II. History and demography. Yellowstone National Park Report, 182 pp. King, J. L., and Jukes, T. H. (1969). Non-Darwinian evolution: Random fixation for selectively neutral alleles. Science 164:788. Kojima, K., Gillespie, J. H., and Tobari, Y. N. (1970). A profile of Drosophila species"enzymes assayed by electrophoresis. I. Number of alleles, heterozygosities and linkage disequilibrium in glucose-metabolizing systems and some other enzymes. Biochem. Genet. 4:627. Manlove, M. N., Avise, J. C, Hillestad, H. O., Ramsey, P. R., Smith, M. H., and Straney, D. O. (1976). Starch gel etectrophoresis for the study of population genetics in white-tailed deer. Proc. 29th Ann. Conf. S.E. Game and Fish Comm. 29:392. Manlove, M. N., Baccus, R., Pelton, M. R., Smith, M. H., and Gruber, D. (1978). Genetic variability in black bear populations. In Martinka, C. J. (ed.), Proceedings o f the 4th International Conference on Bear Research and Management, Wildlife Management Institute, in press. McDermid, E. M., Ananthakirshnan, R., and Agar, N. S. (1972). Electrophoretic investigation of plasma and red cell proteins and enzymes of Macquarie Island elephant seals. Anim. Blood Groups Biochem. Genet. 3:83. Nei, M,, and Roychoudhur3', A. K. (1974a). Sampling variances of heterozygosity and genetic distance. Genetics 76:379. Nei, M., and Roychoudhury, A. K. (1974b). Genetic variation within and between the three major races of man, Caucasoids, Negroids and Mongoloids. Am. J. Hum. Genet. 26:421. Nei, M., Maruyama, T., and Chakraborty, R. (1975). The bottleneck effect and genetic variability in populations. Evolution 29:1. Powell, J. R. (1975). Protein variation in natural populations of animals. Evol. Biol. 8:79. Ryman, N., Beckman, G., Bruun-Petersen, G., and Reuterwall, C. (1977). Variability of red cell enzymes and genetic implications of management policies in Scandinavian moose (Alces alces). Hereditas 85:157. Setander, R. K. (1976). Genie variation in natural populations. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 21-45. Selander, R. K., and Kaufman, D. W. (1973). Genic variability and strategies of adaptation in animals. Proc. Natl. Acad. Sci. 70:1875.
Heterozygosity in Yellowstone Park Elk
657
Selander, R. K., Smith, M. H., Yang, S. Y., Johnson, W. E., and Gentry, J. B. (1971). IV. Biochemical polymorphism and systematics in the genus Peromyscus. I. Variation in the old-field mouse (Peromyscus polionotus). Stud. Genet. VI: Univ. Texas Publ. 7103:49. Soule, M. (1976). Allozyme variation: Its determinants in space and time. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 60-77. Valentine, J. W. (1976). Genic strategies of adaptation. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 78 94. Ward, R. D. (1977). Relationships between enzyme heterozygosity and quaternary structure. Biochem. Genet. 15:123.
Heterozygosity in Yellowstone Park Elk, Cervus canadensis D. G. Cameron 1 and E. R. Vyse 1 Received 7 Sept. t977--Fina118 Jan. 1978
Protein products of 24 loci from the genomes of Yellowstone Park elk were analyzed by electrophoresis. Heterozygosity was detected in only one system, making elk much less polymorphic than eastern whitetailed deer. Data for several other large mammals are compared with those for elk and reveal similarly low levels of isozymic variation. The data are consistent with the fine-grained niche theory but difficult to reconcile with bottlenecks and genetie
drift. KEY WORDS: isozymes; mammals; heterozygosity; polymorphism; elk.
INTRODUCTION Surveys of isozymes in natural populations of sexually reproducing animals have usually revealed large reservoirs of genetic variability (Selander, 1976; Powell, 1975). Small vertebrates frequently contain less variability than insects or marine invertebrates. In comparison, little is known about the genetic structure of large mammals, particulai'ly western North American big game ungulate species. Although their total population numbers are large, the harvest of big game in North America is attained by public hunting over extensive areas, making the collection of fresh tissue samples difficult. At irregular intervals, however, climatic conditions force elk to emigrate out of Yellowstone National Park in Wyoming, presenting an unusual opportunity to collect specimens. In 1973-1975 intensive elk hunts were allowed in the Gallatin River Canyon west of the Park, and in January 1976 a special hunt 1 Department of Biology, Montana State University, Bozeman, Montana, 59717. 651 0006-2928/78/0800.0651505.00[0©1978PlenumPublishingCorporation
652
Cameron and Vyse
took place near Gardner, Montana, north of the Park, allowing access to different segments of the Yellowstone herd. We report the results of electrophoretic studies conducted on tissues collected from entrails left by hunters during these hunts and also from tissues obtained from a Yellowstone-derived herd inhabiting the Big Belt Mountains near Cascade, Montana. The level of heterozygosity found in Cervus canadensis will be compared with available genetic data on other large mammals. MATERIALS AND METHODS Samples were collected on the day of the kill, either while the hunters were dressing their game or as soon after as possible. Usually entrails were left on frozen ground or snow, which helped to minimize enzyme degradation. When possible, samples of heart, muscle, liver, kidney, and blood were taken. Blood samples were frequently obtainable from the heart. Tissue samples were frozen immediately on dry ice and stored at - 50 C. Blood samples were kept on ice and later centrifuged to separate cells and serum before storing at - 50 C. The number of specimens analyzed differed for each protein system but varied between 25 and 200. Both sexes and all age groups were included. Horizontal starch gel electrophoresis was performed using the methods reported by Selander et al. (1971) and Manlove et al. (1976). Direct comparisons between white-tailed deer and elk were made during a working visit to the Savannah River Ecology lab by D. G. C. The proteins analyzed by electrophoresis and the abbreviations used are as follows: lactate dehydrogenase, LDH (1.1.1.27); esterase, Est (3.1.1.1); phosphoglucomutase, PGM (2.7.5.1); malate dehydrogenase, M D H (1.1.1.37); phosphoglucoisomerase, PGI (5.3.1.9); glutamate-oxaloacetate transaminase, GOT (2.6.1.1); ph0sphogluconate dehydrogenase, 6PGD (1.1.1.44); glucose-6-phosphate dehydrogenase, G6PD (1.1.1.49); glucose dehydrogenase, G D H (1.1.1.47); sorbitol dehydrogenase, SDH (1.1.1.14); isocitrate dehydrogenase, IDH (1.1.1.42); superoxide dismutase, SOD (1.15.1.1); malic enzyme, ME (1.1.1.40); acid phosphatase, AP (3.1.3.2); albumin, Alb; transferrin, Trf; hemoglobin, Hb. RESULTS Elk genetic variation will be compared with other large mammals in two ways. In Table I, the 24 presumptive genetic loci studied are compared with homologous loci in all other large mammals for which comparable data are available. By restricting the comparisons to homologous loci, the precision by which/~is estimated is decreased, particularly in elephant seals, but the method has merit because different genetic systems are suspected of having different intrinsic h
Heterozygosity in Yellowstone Park Elk
653
+1
+~
o
0
0
0 >
0
2
0
0
0
f~ 0 0
o
+~
+~
~
0
E Q
~ ~
E 0
I
+1
k-,
+t
Cameron and Vyse
654
Table I1. Heterozygosity and Polymorphic Loci in Large Mammals° Speciesb
Loci
Er
p
Reference
Elk Moose~ White-tailed deer Man Northern elephant seal Southern elephant seal Black beara
24 23
0.012+0.012 0.0006 + 0.0002
0.04 0.04
Ryman et al. (1977)
28 74
0.I0+_0.033 0.099 + 0.21
0.32 0.31
Manlove et aL (1976) Nei and Roychoudhury (1974b)
24
0.0
0.0
Bonnell and Selander (1974)
18 16
0.03 _ 0.016 0.02 _+0.025
0.27 0.12
McDermid et at. (t972) Manlove et aL (1978)
a Data for all loci in the reference cited. b Genera and species in order: Cervus canadensis, Alees alces, Odocoileus virginianus, Homo sapiens, Mirounga angustirostris, M. leonina, Ursus americanus. Average of three populations, 2 years. aAverage of three populations, 16 loci.
values irrespective of the species in which they function (Selander, 1976). By these criteria elk appear to be comparatively monomorphic. Only one locus out of 24 is polymorphic (Table I). This locus was polymorphic in all samples and the allele frequencies did not differ between samples. Standard errors o f / t are large in all these studies, so one should be cautious in concluding that significant differences exist among the tabulated species, with the possible exception of eastern white-tailed deer which are highly polymorphic. In Table II the/7 and/~ values are presented on all loci published for large mammals (excluding domestic animals). The/-7 values calculated when all loci are used suggest that elk, moose, bear, and elephant seals fall into one group and that man and whitetail deer are more highly polymorphic. The proportions of polymorphic loci in elk, moose, and northern elephant seals are much lower than in the other species. DISCUSSION In a pioneer study on large mammals, Bonnell and Selander (1974) found no polymorphism in 24 presumptive loci in northern elephant seals. This monomorphy they attributed to a bottleneck effect brought about by the near extinction of the species in the mid-nineteenth century. Elk heterozygosity is not significantly different from that of northern elephant seals, but Yellowstone elk have not experienced a serious bottleneck. Houston (1974) estimates that the northern Yellowstone herd contained at least 4000 individuals and the
Heterozygosity in Yellowstone Park Elk
655
Gallatin herd 1000 individuals throughout the period when game animals were being decimated across western North America. The current herd sizes exceed 10,000 and 2000, respectively. Unfortunately, we cannot accurately estimate Are for these herds, but their effective population numbers are less than their census counts because of overlapping generations, harem breeding behavior, and population subdivision. Nevertheless, using conservative Ne/N ratios, the effective population numbers must have been several hundred or more at and since the nineteenthcentury bottleneck in the Yellowstone herds. Do the low levels of isozyme variation found in large mammals represent a special adaptive genetic strategy, or do they simply reflect stochastic interactions between neutral mutations and genetic drift? If the stochastic explanation is to hold and mutation rates in large mammals are not unusual, then genetic drift is strongly implicated (King and Jukes, 1969). Either the longterm Arewas low in large mammals or recent bottlenecks have rendered them genetically depauperate. Nei et al. (1975) have shown that bottlenecks can produce surprisingly little short term dimunition in heterozygosity. For example, a sample of only two individuals drawn from a randomly mating population should contain 75% of the heterozygosity found in the parent population, a sample of ten should contain 95%, and a sample of 100 should contain 99.95%. Nei's argument leads us to conclude that today's low levels of heterozygosity in northern elephant seals, moose, or elk probably were not generated by nineteenth-century bottlenecks but more likely by population subdivision or inbreeding of long duration if neutralist theory is applicable at all. /?values calculated using all of the loci available (Table II) are larger than those calculated in Table I. Variation does not appear to be randomly distributed among the loci amenable to analyses by electrophoreses, but polymorphic systems do not group conveniently by function (Gillespie and Kojima, 1968), substrate (Kojima et al., 1970), or quaternary structure (Ward, 1977). Unpublished data on polar bears, Thalarctos maritimus (Allendorf et al., 1978), suggest that this large mammal is also relatively monomorphic. All of these findings seem inconsistent with the neutral allele theory unless by some ecological constraint large mammals have small effective population sizes. Several niche or adaptational theories of population heterozygosity have been reviewed by Soule (1976) and Valentine (1976). We find little in the environmental amplitude or resource stability theories to explain low heterozygosity in large mammals. There is, however, consistency with Selander and Kaufman's (1973) prediction that low heterozygosity would be found in organisms experiencing fine-grained environmental variation because of their high mobility. There is even consistency in the different/? values between the highly
656
Cameron and Vyse
m o b i l e elk a n d m o r e s e d e n t a r y white-tailed deer. A m o r e c o m p r e h e n s i v e survey o f N o r t h A m e r i c a n C e r v i d a e c o u l d be revealing in this regard.
ACKNOWLEDGMENTS W e express o u r a p p r e c i a t i o n to the M o n t a n a State F i s h a n d G a m e for help in collecting samples, A s s o c i a t e d Universities o f O a k R i d g e Visiting F e l l o w P r o g r a m for travel s u p p o r t , a n d Dr. M. H. S m i t h a n d M. M a n l o v e for assistance at the S a v a n n a h R i v e r E c o l o g y L a b o r a t o r y .
REFERENCES
AUendorf, F. W., Christiansen, F. B., Eanes, W, F., and Frydenberg, O~(1978). Homozygosity in the polar bear. Science (submitted). Bonnell, M. L., and Selander, R. K. (1974). Elephant seals: Genetic variation and near extinction. Science 184:908. Gillespie, J. H., and Kojima, K. (1968). The degree of polymorphism in enzymes involved in energy production compared to that in nonspecific enzymes in two Drosophila ananassae populations. Proc. NatL Acad. Sci. 61:582. Houston, D. (1974). The northern Yellowstone elk. Parts I and II. History and demography. Yellowstone National Park Report, 182 pp. King, J. L., and Jukes, T. H. (1969). Non-Darwinian evolution: Random fixation for selectively neutral alleles. Science 164:788. Kojima, K., Gillespie, J. H., and Tobari, Y. N. (1970). A profile of Drosophila species"enzymes assayed by electrophoresis. I. Number of alleles, heterozygosities and linkage disequilibrium in glucose-metabolizing systems and some other enzymes. Biochem. Genet. 4:627. Manlove, M. N., Avise, J. C, Hillestad, H. O., Ramsey, P. R., Smith, M. H., and Straney, D. O. (1976). Starch gel etectrophoresis for the study of population genetics in white-tailed deer. Proc. 29th Ann. Conf. S.E. Game and Fish Comm. 29:392. Manlove, M. N., Baccus, R., Pelton, M. R., Smith, M. H., and Gruber, D. (1978). Genetic variability in black bear populations. In Martinka, C. J. (ed.), Proceedings o f the 4th International Conference on Bear Research and Management, Wildlife Management Institute, in press. McDermid, E. M., Ananthakirshnan, R., and Agar, N. S. (1972). Electrophoretic investigation of plasma and red cell proteins and enzymes of Macquarie Island elephant seals. Anim. Blood Groups Biochem. Genet. 3:83. Nei, M,, and Roychoudhur3', A. K. (1974a). Sampling variances of heterozygosity and genetic distance. Genetics 76:379. Nei, M., and Roychoudhury, A. K. (1974b). Genetic variation within and between the three major races of man, Caucasoids, Negroids and Mongoloids. Am. J. Hum. Genet. 26:421. Nei, M., Maruyama, T., and Chakraborty, R. (1975). The bottleneck effect and genetic variability in populations. Evolution 29:1. Powell, J. R. (1975). Protein variation in natural populations of animals. Evol. Biol. 8:79. Ryman, N., Beckman, G., Bruun-Petersen, G., and Reuterwall, C. (1977). Variability of red cell enzymes and genetic implications of management policies in Scandinavian moose (Alces alces). Hereditas 85:157. Setander, R. K. (1976). Genie variation in natural populations. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 21-45. Selander, R. K., and Kaufman, D. W. (1973). Genic variability and strategies of adaptation in animals. Proc. Natl. Acad. Sci. 70:1875.
Heterozygosity in Yellowstone Park Elk
657
Selander, R. K., Smith, M. H., Yang, S. Y., Johnson, W. E., and Gentry, J. B. (1971). IV. Biochemical polymorphism and systematics in the genus Peromyscus. I. Variation in the old-field mouse (Peromyscus polionotus). Stud. Genet. VI: Univ. Texas Publ. 7103:49. Soule, M. (1976). Allozyme variation: Its determinants in space and time. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 60-77. Valentine, J. W. (1976). Genic strategies of adaptation. In Ayala, F. J. (ed.), Molecular Evolution, Sinauer Associates, Sunderland, Mass., pp. 78 94. Ward, R. D. (1977). Relationships between enzyme heterozygosity and quaternary structure. Biochem. Genet. 15:123.
