Considering the multinomial sampling of genotypes, unbiased estimators of various gene diversity measures in subdivided populations are presented. Using these quantities, formulae for estimating Wright's fixation indices (FIS, FIT, and FST) from a finite sample are developed.

No abstract

Abstract-Free-ranging mammals near the Chornobyl nuclear reactor are experiencing substantial radiation dose rates from intramuscular concentrations of 134,137 Cs and skeletal 90 Sr. Radiocesium concentrations averaged 3,200 Bq/g of dry muscle, compared to a mean of 297 Bq 90 Sr/g in bone for mammals in the Exclusion Zone, a region of restricted human activity surrounding the reactor. Estimates of dose rates from intramuscular sources of radiocesium averaged 2.4 mGy/d within 8 km of the reactor and ranged as high as 60 mGy/d. Overall dose rates from internal 90 Sr for mammals in the Exclusion Zone averaged 1.0 mGy/d, although doses to specific tissues are likely much higher. Mammals captured 30 km southeast of the reactor averaged only 2 Bq/g of muscle and were receiving an average of 1.4 Gy/d from internal radiocesium. Dramatic variation exists in the spatial pattern of radiocesium in areas immediately surrounding the reactor and within and between remediated and unremediated regions. The variance of 90 Sr for taxa among sites was significantly less than that for 134,137 Cs. Thermoluminescent dosimeters placed on free-ranging mice showed that dose rates from external sources of radiation were much greater than the dose rates from internal sources of radiocesium. Estimated dose rates in very small areas of the Chornobyl region exceed those reported to impede reproductive success in mammals.

No abstract

Abstract-At radioactive sites, at least two mechanisms may affect the genetic diversity of populations of a given species. Increased mutation rates due to radiation exposure may increase the amount of genetic diversity in a population. Alternatively, population bottlenecks exacerbated by environmental degradation may lead to a reduction of diversity. The relationship between these two contradictory forces is complex. To explore this relationship, long-term monitoring of a genetic marker within a population is needed. To provide baseline data on the population genetics of the bank vole (Clethrionomys glareolus) living in the most contaminated regions at Chornobyl, Ukraine, we have sequenced 291 base pairs of the mitochondrial DNA control region. Bank voles were chosen as a model system because they have the highest levels of internal dose of cesium-134, cesium-137, and strontium-90 within the Chornobyl exclusion zone. We sampled three geographic sites, which were Oranoe, a reference site with virtually no radioactive contamination (Ͻ2 Ci/km 2 ), and two highly contaminated sites, Glyboke Lake and the Red Forest (both 1,000 Ci/ km 2 ). Genetic diversity in the population from Red Forest (0.722 Ϯ 0.024) was significantly greater than at the Oranoe reference site (0.615 Ϯ 0.039), while genetic diversity at Glyboke Lake (0.677 Ϯ 0.068) was intermediate. It is concluded that long-term studies of historical and demographic characteristics for experimental and reference populations are required in order to employ population genetics to understand the biological impact of environmental contaminants on the genetics of natural populations.

No abstract

Abstract. Genetic markers that differ in mode of inheritance and rate of evolution (a sex-linked Z-specific microsatellite locus, five biparentally inherited microsatellite loci, and maternally inherited mitochondrial [mtDNA] sequences) were used to evaluate the degree of spatial genetic structuring at macro-and microgeographic scales, among breeding regions and local nesting populations within each region, respectively, for a migratory sea duck species, the spectacled eider (Somateria fisheri). Disjunct and declining breeding populations coupled with sex-specific differences in seasonal migratory patterns and life history provide a series of hypotheses regarding rates and directionality of gene flow among breeding populations from the Indigirka River Delta, Russia, and the North Slope and YukonKuskokwim Delta, Alaska. The degree of differentiation in mtDNA haplotype frequency among breeding regions and populations within regions was high ( CT ϭ 0.189, P Ͻ 0.01; SC ϭ 0.059, P Ͻ 0.01, respectively). Eleven of 17 mtDNA haplotypes were restricted to a single breeding region. Genetic differences among regions were considerably lower for nuclear DNA loci (sex-linked: ST ϭ 0.001, P Ͼ 0.05; biparentally inherited microsatellites: mean ϭ 0.001, P Ͼ 0.05) than was observed for mtDNA. Using models explicitly designed for uniparental and biparentally inherited genes, estimates of spatial divergence based on nuclear and mtDNA data together with elements of the species' breeding ecology were used to estimate effective population size and degree of male and female gene flow. Differences in the magnitude and spatial patterns of gene correlations for maternally inherited and nuclear genes revealed that females exhibit greater natal philopatry than do males. Estimates of generational female and male rates of gene flow among breeding regions differed markedly (3.67 ϫ 10 Ϫ4 and 1.28 ϫ 10 Ϫ2 , respectively). Effective population size for mtDNA was estimated to be at least three times lower than that for biparental genes (30,671 and 101,528, respectively). Large disparities in population sizes among breeding areas greatly reduces the proportion of total genetic variance captured by dispersal, which may accelerate rates of inbreeding (i.e., promote higher coancestries) within populations due to nonrandom pairing of males with females from the same breeding population. Recent advances in molecular biology have greatly increased the number and accessibility of molecular techniques capable of resolving variation in genetic markers with contrasting modes of inheritance. Comparative analyses of spatial distributions and the depths of genealogical topologies across multiple markers have provided strong support linking contemporary population structure with historical processes (Wilson et al. 1985; Avise et al. 1987). Behavioral events linked to the timing of pair bonds, degree of philopatry, and dispersal strategies can also play significant roles in defining how genetic variation is partitioned within and among populations and may be rea...

Considerable controversy surrounds the importance of inbreeding in natural populations. The rate of natural inbreeding and the influences of behavioral mechanisms that serve to promote or minimize inbreeding (e.g., philopatry vs. dispersal) are poorly understood. We studied inbreeding and social structuring of a population of black-tailed prairie dogs (Cynomys ludovicianus) to assess the influence of dispersal and mating behavior on patterns of genetic variation. We examined 15 years of data on prairie dogs, including survival and reproduction, social behavior, pedigrees, and allozyme alleles. Pedigrees revealed mean inbreeding coefficients (F) of 1-2%. A breeding-group model that incorporated details of prairie dog behavior and demography was used to estimate values of fixation indices (F-statistics). Model predictions were consistent with the minimization of inbreeding within breeding groups ("coteries," asymptotic F = -0.18) and random mating within the subpopulation ("colony," asymptotic F = 0.00). Estimates from pedigrees (mean F = -0.23, mean F = 0.00) and allozyme data (mean F = -0.21, mean F = -0.01) were consistent with predictions of the model. The breeding-group model, pedigrees, and allozyme data showed remarkably congruent results, and indicated strong genetic structuring within the colony (F = 0.16, 0.19, and 0.17, respectively). We concluded that although inbreeding occurred in the colony, the rate of inbreeding was strongly minimized at the level of breeding groups, but not at the subpopulation level. The behavioral mechanisms most important to the minimization of inbreeding appeared to be patterns of male-biased dispersal of both subadults and adults, associated with strong philopatry of females. Incest avoidance also occurred, associated with recognition of close kin via direct social learning within the breeding groups.