Translocation history and genetic diversity in reintroduced bighorn sheep

Because genetic diversity provides the substance for adaptation and evolution and its decline signifies the potential for deleterious effects on demography, biologists must understand how management action can facilitate or hinder the retention of genetic diversity at the level of the population being managed. We assessed genetic diversity in 8 reintroduced populations of bighorn sheep using 16 microsatellite markers and a 515-base-pair segment of the mitochondrial control region. Populations were categorized by their translocation histories: first-order populations were those established directly from large source populations, second-order populations were established using individuals from first-order populations, and populations with mixed translocation histories were those established or supplemented with sheep from more than 1 sample on a source population. Nuclear and mitochondrial datasets yielded complementary signals of declining genetic diversity (mixed > first order > second order) that differed predictably in magnitude. Our suite of microsatellites revealed that populations with mixed translocation histories had greater allelic richness (AR) and expected heterozygosity (HE) than second-order populations, but we found no statistical differences between mixed:first order or first:second order population pairs. Mitochondrial diversity, however, was limited to populations with mixed translocation histories. Similarly, we detected significant differentiation (FST) among most populations using data from microsatellites, but found major differentiation in mitochondrial diversity. All first-order and second-order populations shared a single haplotype, whereas mixed populations contained 6 haplotypes. Finally, estimates of effective population size (Ne) derived from our microsatellite data were uniformly low (range 9–27), indicating that the maintenance of genetic diversity in the reintroduced populations of bighorn sheep in our study likely will require management action; possibly including future translocations and improvements in natural connectivity among populations. © 2013 The Wildlife Society.