Comparative Population Genetics of Two Gila River Cyprinids

Authors: Tyler J. Pilger, Thomas F. Turner

Year: 2010 (xlii)

Abstract

The upper Gila River basin in southwest New Mexico, USA is one of the few unimpounded drainage basins remaining in North America and provides a stronghold for a unique and largely endemic fish fauna. However, coincident with introduction of nonnative predators, distributions of native fishes have severely declined. Reaches with high predator densities could inhibit dispersal of native fishes, disrupt migration corridors, and isolate populations by reducing gene flow and decreasing genetic diversity. We used microsatellite loci to examine population structure of two cyprinids with similar life history strategies, but with different current distributions. Spikedace, Meda fulgida, is a federally listed species that is found in only a few sites in the Gila River of New Mexico, whereas longfin dace, Agosia chrysogaster, is common and widely distributed. We collected fin clips from spikedace and longfin dace at three and seven localities, respectively, over a 96 km longitudinal section of the Gila River of New Mexico. We compared population substructure of the rare spikedace with that of the common longfin dace. Both species showed similar observed and expected heterozygosity. Although FST of both species indicated significant genetic structure between upstream and downstream sites, the more common longfin dace showed less genetic structure than the rare spikedace, suggesting there is more gene flow between reaches with longfin dace than spikedace. Preliminary data indicate that genetic divergence most likely results from isolation by geographic distance. Future work will examine the possibility that gene flow is disrupted by other abiotic or biotic factors related to habitat suitability and/or negative effects of predation.