Comparative phylogeography of spring invertebrates from the northern Chihuahuan Desert

Comparative phylogeography can reveal current and historical patterns of diversity that are shared among taxonomic groups. Springs of the northern Chihuahuan Desert contain significant endemicity among benthic invertebrates. We are conducting phylogeographic analysis of mtDNA for two taxa (amphipods of the genus Gammarus, and flatworms of the genus Girardia) from springs in southeastern New Mexico and west Texas. Amphipod populations showed high degrees of differentiation; each spring system contained an endemic lineage. Amphipods also exhibited an isolation-by-distance pattern within spring systems, but no association of genetic distance and geographic distance among spring systems. This pattern is likely due to geographic isolation resulting in low gene flow, along with genetic drift. Because amphipods and flatworms both have limited dispersal capabilities, the degree of isolation and drift should be similar for both taxa. We will compare phylogeographic patterns in these groups. Desert springs are threatened by anthropogenic activities; there is a great need to identify evolutionarily significant units that merit conservation action. If these disparate invertebrate groups show similar patterns, it is likely that such patterns will extend across a broad array of taxonomic groups. As such, these desert spring ecosystems will contain large numbers of species that are threatened with extinction.