Genetic evaluation of captive populations of endangered species and merging of populations: Gila topminnows as an example

To avoid extinction, captive populations of a number of endangered species have been established. While in captivity, these populations have been managed to retain genetic variation although direct evaluation of this strategy using molecular markers is not common. In addition, when the number of founders for a captive population is small, other founders or populations may be added to increase genetic variation. Here we examined refugial populations of the endangered Gila topminnow (Poeciliopsis occidentalis) from 4 locations in the southwestern United States. We found that over 5 years (about 10 generations), genetic variation as measured by 5 microsatellite loci was not lost, presumably because the adult census population size was 500 or greater. In addition, some variation not initially observed was observed later. Some of these variants may have been missed because of sampling but it appears that some may have been contributed by new mutations. In addition, 2 populations of successfully merged ancestry from the 4 source populations were examined. Based on population-specific markers and a quantitative evaluation of ancestry using a likelihood approach, it appears that ancestry from each of the source populations was retained in both populations.