Development of twenty-one novel microsatellite loci for Gila topminnow, Poeciliopsis occidentalis occidentalis

Gila topminnow (Poeciliopsis occidentalis occidentalis) was once highly abundant throughout the Lower Colorado River Basin of the southwestern United States. However, this Sonoran Desert endemic suffered extreme population declines over the past century because of habitat degradation and nonnative species introductions. Much of the prior conservation genetic work conducted on the species relied upon a small number of microsatellite loci; many exhibiting low variability in extant populations. Consequently, there was a need for additional microsatellite loci to provide high-resolution delimitation of populations for conservation purposes.

Paired-end Illumina sequencing was utilized to screen the Gila topminnow genome for novel microsatellite loci. We identified 21 novel loci that exhibited no deviations from expectations of genetic equilibrium, and cross-amplified in Yaqui topminnow (P. o. sonoriensis). These loci were amplified from 401 samples representing eight populations of Gila topminnow and Yaqui topminnow. Although diversity was low for all populations (observed heterozygosity = 0.12 to 0.45), these novel markers provided ample power to identify population of origin for each individual in Bayesian assignment tests.

This novel set of microsatellite loci provide a useful genetic tool to assess population genetic parameters of the endangered Gila topminnow and delineate populations for identifying conservation priorities. The cross-amplification of these loci in Yaqui topminnow shows promise for application to other Poeciliopsis species of Mexico and Central America.