Genetics of insular Peromyscus leucopus populations at Norris Lake, Tennessee

A total of 138 Peromyscus leucopus were sampled from 9 island and 3 mainland sites at Norris Lake in eastern Tennessee. Liver and muscle extracts were used to identify 17 allozyme loci using starch gel electrophoresis, 9 of these loci were polymorphic. Using the 8 largest collection of insular mice and the two largest collections of mainland mice it was determined that the insular populations are no less genetically variable (estimated as P , proportion of polymorphic loci, and H₀, mean individual heterozygosity) than the mainland populations. Genetic identities were not significantly correlated with geographical distances between island pairs. Gene flow is the probable mechanism that prevents these populations from diverging. Significant differences between island and mainland heterogeneity and among subpopulation genetic variance (F_st) estimates could not be shown. Significant genetic heterogeneity was found among the insular populations at the 4 most robustly polymorphic loci (EST, αGPD, IPO, and 6-PGD). Social structuring of these populations may account for the significant genetic heterogeneity among them. A pattern of heterozygote deficiency was found at the 6-P6D and EST loci in both insular and mainland populations. There are 4 possible explanations for these results: 1) negative heterosis, 2) population structuring, 3) Wahlund effect, and 4) the presence of "null" alleles. It could not be shown that insular P. leucopus populations were any more subject to the stochastic processes usually attributed to island habitation than the mainland populations at Norris Lake. A large difference was found between F_st estimates of males from 6 islands with the largest collections (F_st = .0399) and females from 4 islands with the largest collections (F_st = .1929). Sexual differences in dispersion probably account for these results. Males move further than females and are, therefore, probably less closely related to one another within a sample.