Conservation biology of the black-footed ferret (Mustela nigripes): Changes in genetic diversity and morphology before, during and after a population bottleneck

The decrease of a population to a small size, a population bottleneck, is a process central to conservation biology. Although the theoretical genetic and phenotypic consequences of a population bottleneck are well understood, empirical demonstration has been rare. Likewise, the theoretical underpinnings for the strategies used to manage small populations have been modeled extensively, but the efficacy of these strategies to conserve genetic variability and limit phenotypic changes has received less attention. I documented genetic and phenotypic changes due to a population bottleneck in the critically endangered blackfooted ferret (Mustela nigripes) in an effort to better understand the processes of population decline and small population size. I used 24 microsatellite markers developed for various mustelid species and black bear (Ursus americanus) to describe spatial and temporal patterns of genetic diversity in historical populations of pre-bottleneck black-footed ferrets, in the founders of the captive population and in two reintroduced populations. I analyzed genetic diversity in two sister species, the European polecat ( M. putorius) and the steppe polecat (M. eversmanni). I measured skull size and fluctuating asymmetry in bilateral traits of pre- and post-bottleneck black-footed ferrets. Historical populations showed spatial structure in patterns of genetic diversity. Anthropogenic disturbances were correlated with local decline in genetic diversity, and a population bottleneck in the last population contributed to further declines in genetic diversity. Pre-bottleneck animals had genetic diversity comparable to Old World ferrets, but post-bottleneck black-footed ferrets had less genetic diversity than either Old World ferret. Once taken into captivity, however, genetic diversity ceased to decline; captive and wild-born individuals retained the allelic and gene diversity present in the founders. Genetic conservation appeared to be the result of using the mean kinship strategy of genetic management; variance in individual mean kinship decreased between 1991 and 1999. Phenotypic changes occurred to captive animals. Captive black-footed ferrets had skulls 6--10% smaller than, but less fluctuating asymmetry than pre-captive animals. It is unclear whether the change in skull size was due to unintentional selection or due to environmental factors. I attributed the decrease in fluctuating asymmetry to a decrease in energetic stress associated with captivity.