Molecular variation and evolutionarily significant units in the endangeredGila topminnow

Determining evolutionarily significant units in endangered species is one o f the most significant challenges facing conservation biology Often genetic information has been used as the primary basis of recommendations for evol utionarily significant units, but these data should be evaluated carefully and used in conjunction with other information. The endangered Gila topminn ow (Poeciliopsis. o. occidentalis) has been the subject of extensive conser vation biology research and genetic investigation. We extended these data t o highly variable genetic markers, examined variation in microsatellite loc i, and compared it with previous measures of genetic diversity for the Gila topminnow from the four watersheds in Arizona in which they are still natu rally extant. Fish from Monkey Spring were the most highly differentiated f rom the other populations. Overall, the amounts and patterns of genetic var iation were consistent with known historical and physical differences among sites. the four watersheds are highly physically isolated from one another and differ in a number of important factors in their physical habitat biot a, and the life-history of the topminnows. Based on these geographic patter ns and the genetic results, we recommend that the four watersheds all be ma naged and conserved separately.