Genetic Characterization of Variation in Captive and Wild Woundfin

The woundfin Plagopterus argentissimus is an endangered species that has been extirpated front most of its historic range in the Colorado River basin, now occurring only in the main-stem Virgin River. In 1987, refugial stocks were established at the Dexter National Fish Hatchery and Technology Center (Dexter) as a hedge against extinction. Offspring from the captive populations have been released in the Virgin River since 1993, by which time wild populations had markedly declined. This study was conducted to determine whether the stocks at Dexter have retained the character of the wild donor stocks as indicated by the distribution of genetic variation within and between stocks. The genetic composition of captive populations may diverge from that of wild donor populations, even over relatively short time periods, owing to founder effect, genetic drift, and selection for traits that are advantageous in captivity. Captive and wild stocks were surveyed, both spatially and temporally, using 10 microsatellite markers developed at Dexter. Microsatellite markers are considered selectively neutral, and this study measured genetic changes due to random evolutionary processes (given our approach, it would be unlikely to identify changes at nonneutral loci due to selection). Overall, the woundfin exhibited high levels of genetic variation for a freshwater species. The samples from the captive and wild woundfin populations had similar levels of heterozygosity, but generally the captive populations had fewer alleles. A comparison of composite samples of captive stocks and recent wild stocks yielded an F-ST value of 0.004. Although statistically significant, this level of genetic distance is typical of well-mixed or undifferentiated stocks. After 20 years of captive propagation, the stocks at Dexter do not appear to have been impacted by founder effect or genetic drift.