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Variation and differentiation among populations provide a framework to decipher how populations are, or are not, changing due to gene flow, genetic drift, and selection. The sagebrush least chipmunk (Tamias minimus scrutator) is distributed in arid and semi-arid habitats throughout much of the Great Basin and adjacent regions. The broad distribution and variation in elevation of populations make this a good system to assess population variation and the forces shaping differentiation. Here, we use allozyme and morphological datasets to: 1) assess the relative roles of geographic locality and elevation of populations in shaping population structure; 2) examine the level of differentiation of peripheral and isolated populations; and 3) compare the genetic and morphological signals of population variation and structure. We sampled 312 individuals from 12 T. minimus scrutator populations and other areas of their distribution. Individuals were measured for 27 genetic and 61 morphological traits. These datasets were analyzed to determine the distribution of variation and the differentiation among populations and tested for correlations with geographic distance and elevation. Multiple approaches were used to thoroughly compare the signals from each dataset. We found 13 polymorphic electrophoretic loci with most of the variation structured among populations within regions. Eight loci exhibited elevational heterogeneity but most high-elevation populations showed no heterogeneity among populations. Thirty-two morphological characters varied among populations but with no discernable trends across regions or elevations. Populations had varying levels of asymmetric distinctness in morphological characters, but there were no significant differences among populations. Morphological and genetic distance measures were correlated and there was some evidence of a correlation of genetic and geographic distance. We also found some correlation of asymmetric distances with morphological or genetic distances at smaller scales. There was substantial variation of genetic and morphological traits among sagebrush least chipmunk populations. Each population had a unique genetic signature and significant morphological differentiation. Our results suggest that genetic drift is contributing to the structure of these populations, with some evidence of selection shaping the distribution of variation at different elevations. The peripheral populations had mixed signals of isolation among the different datasets, with an overall signature suggesting that genetic drift is also driving the variation among these populations. The different measures of population variation yielded inconsistent signals of population structure, highlighting the need for multiple approaches to assess population variation. The variation among sagebrush least chipmunk populations is impacted by a variety of factors and contemporary investigations may reveal populations responding to alterations in habitat and climate.

Substantial genetic divergence was found among chum salmon (Oncorhynchus keta) populations collected from North America and Russia. Five major groups of populations can be identified by geographic region: (1) lower Yukon River summer run; (2) upper Yukon River fall run; (3) Bristol Bay area; (4) Alaska Peninsula; and (5) Russia. Mean heterozygosities were 0.064, 0.062, 0.065, 0.064, and 0.063, respectively; and the percent polymorphic loci values at the 0.99 level were 33.7, 31.3, 32.6, 30.6, and 30.9%, respectively. The hierarchical gene diversity analysis showed that 95.42% of the diversity can be explained by heterogeneity within sites, 1.36% among sites, 0.49% between Yukon River run timing, 1.69% among areas, and 1.04% among countries. The Alaska Peninsula populations are genetically more similar to populations from Russia than to those from western Alaska, and two populations from the upper Yukon River are distinct from other nearby populations. Possible reasons for these findings concern the complex glacial histories of the watersheds.

The dispersion pattern of 360 juvenile white-footed mice, Peromyscus leucopus , from 158 matings was monitored to determine whether dispersal was sufficient to prevent close inbreeding. Dispersal was male-biased with 20% of the daughters remaining in their natal home ranges. Dispersal of sons was not ‘forced’ by adult males, but may have been influenced by the presence of their mothers. One mother-son and five father-daughter pairs had overlapping home ranges during the breeding season, but the maximum number of matings among close relatives was three of 135 (2·2%). Dispersal of juvenile males was sufficient to keep close inbreeding at a minimum. Dispersal did not result from reproductive competition. Pregnant and post-lactating females frequently moved to new home ranges. The reproductive success of immigrants was the same as that of natal residents.

Populations of two species of cricetine rodents, Peromyscus leucopus and P. maniculatus , sampled during a 6-year period were analyzed by electrophoresis for genetic variability at 33 presumptive loci. Population densities fluctuated concurrently for both species during this time period. There were no significant differences in mean heterozygosities, percent polymorphic loci, or average number of alleles per locus between species. During years with high-density populations, the two species were more similar genetically than during years with low to mid-density populations. Two isozyme systems, GDH and CAT, showed little or no difference between species within any 1 year, yet both exhibited highly significant differences among years. Over-all genetic-identity values for the populations among years were higher than genetic-identity values for the species within each year. However, for five isozyme systems (GDH, CAT, IDH-1, SDH, and βNA), genetic identities across species within years were greater than those for among-year comparisons within each species. Genetically, in many respects, these two sympatric species operated as one.

An extensive live-trapping system, consisting of 700 trap stations over 16 ha indicated that a demographic unit or demographically distinct subpopulation of Peromyscus leucopus can occupy an area as large as 13.5 ha or as small as 2.4 ha. The 2.4 ha demographic unit was located in a successional habitat and was characterized by consistently lower densities, winter extinction in four consecutive years, and a large number of immigrants relative to emigrants. Significant heterogeneity in allelic frequency and significant F st values indicated that genetic structure occurred on the same scale. However, the units of genetic heterogeneity did not correspond to the demographic units.

Electrophoretic variation at 19 loci was examined in 10 species of even-toed ungulates (Artiodactyla). Mean level of genetic heterozygosity (H) and proportion of polymorphic loci (P) in large mammals do not differ from the values for mammals in general (H = 0.033 and P = 0.128). Level of genetic variability among species does not appear to be correlated with body size within the large mammals. Large grazing mammals are closely related genetically; all species share at least some electromorphs at some loci. Genetic relationships are in general agreement with most previously accepted systematic relationships, but there are some exceptions. Species of the Cervidae and Antilocapridae are genetically closer than the latter is to the Bovidae even though the Antilocapridae and Bovidae belong to the same superfamily (Bovoidea). Genetic distance and amount of chromosomal rearrangement are correlated in the large grazing mammals. Chromosome rearrangement and accumulation of point mutations are correlated processes in large mammals.

Because of the complex manner in which selection may occur, its measurement is a formidable problem. Adequate measurements require characterization of all selection components, age-dependence of fertility and mortality, immigration and emigration, and the temporal constancy and geographic variation of these patterns (Lewontin, 1974). One of the most comprehensive methods to detect selection in natural populations is based on analyses of selection components of natural polymorphisms in population samples which include mother-offspring combinations. The Christiansen-Frydenberg selection component analysis (SCA) (Christiansen and Frydenberg, 1973, 1976) consists of a hierarchy of hypotheses and tests which together characterize the modes of selection acting on particular chromosomal segments. Because it is based on one randomly selected progeny per mother-offspring combination, the hypotheses are interdependent. As a consequence, testing along the sequence is terminated at the first significant deviation from a null hypothesis. In addition, tests for gametic and sexual selection are confounded (Christiansen and Frydenberg, 1973; Nadeau et al., in press). Nadeau et al. (in press) showed that by analyzing all progeny of each mother-offspring combination, all tests except gametic selection in females are independent, gametic selection in males can be unambiguously detected, and even with analyses of entire litters

mouse (P. polionotus). Univ. Texas Publ. 7103: 49-90. SNYDER, L. R. G. 1978a. Genetics of hemoglobin in the deer mouse, Peromsycus maniculatus. I. Multiple aand,f3-globin structural loci. Genetics 89:511-530. SNYDER, L. R. G. 1978b. Genetics of hemoglobin in the deer mouse, Peromyscus maniculatus. II. Multiple alleles at regulatory loci. Genetics 89: 531-550. SNYDER, L. R. G. 1980a. Evolutionary conservation of linkage groups: additional evidence from murid and cricetid rodents. Biochem. Genet. 18: 209-220. SNYDER, L. R. G. 1980b. Closely linked alphachain hemoglobin loci in Peromyscus and other mammals: speculations on the evolution of duplicate loci. Evolution 34:1077-1098.

The demographic characteristics and consequences of dispersal were studied in a population of Peromyscus leucopus with an extensive system of live-trapping grids. Dispersal events of up to 1 km (minimum straight-line distance) could be detected with this system. Although the absolute numbers of dispersers increased with density, relative indices of dispersal showed no correlation with population density. Two classes of dispersers could be detected: (1) dispersers colonizing an area which annually goes extinct were a random sample of the resident population with respect to age structure, sex ratio and reproductive condition, (2) dispersers which were not of this colonizing group tended to be biased toward adult age classes and the sex ratio was significantly biased toward males. After recolonization of the vacant area, dispersal was not preferentially directed to regions of lower density. It is suggested that dispersal in this species is more intimately related to social interactions and the avoidance of inbreeding than to local density. INTRODUCTION Studies of dispersal in small mammals have focused on the evolutionary and ecological consequences of movement from the home area (Gaines and McClenaghan, 1980; Tamarin, 1978; Riggs, 1979; Gadgil, 1971; Lidicker, 1975; Fairbairn, 1978). Various authors have discussed the evolution of behavior in which the organism leaves the familiar home area for unknown and unguaranteed benefits elsewhere (Lidicker, 1975; Gaines and McClenaghan, 1980). For saturation dispersers (Lidicker, 1975) emigration may truly be a desperation move at high density which is beneficial only when the consequences of staying are likely to be dire. Presaturation dispersers (Lidicker, 1975) emigrate prior to the attainment of carrying capacity and thus may receive other benefits. One example would be the genetic advantages of avoiding inbreeding (Haigh, 1983). In addition, presaturation dispersers might benefit from attaining a new and perhaps higher social status in the new home area. There may also be advantages in terms of reproductive value if the disperser locates a low density area which has the potential for population increase. These evolutionary advantages have been considered in relation to the existence of demographic heterogeneity which dispersers can exploit (Wiens, 1976; Roff, 1974a and 1974b; Levin, 1976). That such heterogeneity exists is not in doubt as numerous examples have been documented (Anderson, 1970). However, few dispersal studies have documented the pattern of local habitat heterogeneity and related the patterns of movement to it, particularly in an unmanipulated system. The present study attempted to do this for a population of Peromyscus leucopus. One aspect of such habitat heterogeneity may be a dispersal sink which Lidicker (1975) defines as a region of empty or unsuitable habitat to which dispersal may be directed and in which survival is low.

Genotypic proportions and heterozygosity of beta-hemoglobin in a white-tailed deer (Odocoileus virginianus) herd were secured to estimate the association of sex, location, year, and age with the variability of this locus. No differences (P > 0.05) in heterozygosity or genotypic frequencies occurred between sexes or among 5 regions on the Savannah River Plant. Heterozygote proportions among 2,455 deer varied (P 3.5 years) had higher (P < 0.05) frequency of heterozygotes than those of younger age-classes. The association of age and heterozygosity did not differ among regions or between years. Because age is an important determinant of social status in deer, shifts in the age structure of the herd may increase competitive interactions and, thus, be the source of selection for the changes in heterozygosity. J. WILDL. MANAGE. 46(4):983-990 Genetic variability in the white-tailed deer is higher than in other large mammals (Smith et al. 1976). Natural selection helps maintain genetic variability in this species, because the type, direction, and intensity of selection vary through space and time (Baccus et al. 1977). Important characters such as reproduction, aggressive behavior, and survivorship in birds and mammals are associated with heterozygosity (Krebs et al. 1973; Smith et al. 1975, 1978; Garten 1976; Johns et al. 1977; Baker and Fox 1978). These characters are intimately associated with the efficiency of resource use, and resource limitation may be the source of selection for heterozygosity. Differential selection of animals from various cohorts, sexes, or age-classes could also cause high heterozygosity in deer. Susceptibility to disease and competitive ability for limited resources also differ among life stages (Verme 1977). Few studies have documented genetic changes with age. Tinkle and Selander (1973) found age-specific selection respons ble for changes in genotypic proportions in a lizard population; heterozygosity was considerably higher in the oldest age-class. In white-tailed deer, no genetic differences for beta-hemoglobin (PHB) were found among animals of different ages from Iowa and Nebraska (Miller et al. 1965). However, Ramsey et al. (1979:139) reported age-specific differences in the heterozygosity of PHB in de r from the Savannah River Plant (SRP). Deer of each sex and age-class are also characterized by different gene frequencies for other loci (Manlove et al. 1975, Ramsey et al. 1979). Thus, a deer herd seems to be composed of genetically heterogeneous groups but this point needs further documentation. The objectives of our study were to test 4 null hypotheses. These were that genotypic proportions of beta-hemoglobin in white-tailed deer do not vary between sexes, and among ageclasses, regions of the SRP, and years. We thank personnel of the U.S. For1 Present address: Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409. J. Wildl. Manage. 46(4):1982 983 This content downloaded from 157.55.39.159 on Sun, 18 Sep 2016 05:44:40 UTC All use subject to http://about.jstor.org/terms 984 HETEROZYGOSITY IN WHITE-TAILED DEER * Chesser et al. estry Station, SRP and our colleagues at the Savannah River Ecology Laboratory for help in the field. Financial support came from contract DE-AC09-76SR00819 between the U.S. Department of Energy and The University of Georgia.