Conservation genetics in aquatic species: General approaches and case studies in fishes and springsnails of arid lands

Many aquatic species have become endangered because of the elimination and fragmentation of their habitat, human alteration of the environment, and introduced species. New applications and insights from genetic studies of endangered species are being used to formulate management plans to prevent extinction of endangered taxa. Here we discuss three applications of genetic techniques to the conservation of endangered aquatic species in the desert Southwest, USA. First, we discuss estimation of long-term effective population size in three endangered big-river fishes, bonytail chub (Gila elegans), humpback chub (G. cypha) and razorback suckers (Xyrauchen texanus), of the lower Colorado River. For all three species, the current census number is much smaller than the estimated effective population size in which these species evolved. Second, we discuss the determination of species, ESUs, and MUs in the endangered Sonoran topminnow. Molecular genetic data show that the Gila and Yaqui topminnows are different species. Experimental examination of pre-mating and post-mating reproductive isolation demonstrates that some reproductive isolation has already developed between these two species. Finally, springsnails (Pyrgulopsis) of the lower Colorado River basin exist only in remote and isolated springs. Examination of molecular variation generally supports the morphological designation of 16 different species, although a few species have several ESUs. There does not appear to be a correlation of genetic and geographic distance between species, suggesting that they are quite old. These genetic studies provide insight into the conservation of these rare aquatic species. Although mitigating ecological factors may be most significant in preventing extinction, genetic studies can provide the evolutionary context for endangered species and identify what units are most in need of conservation.