Comparative population genetics of Gila River fishes: Life history influences on genetic diversity and gene flow

Authors: Tyler J. Pilger, Thomas F. Turner

Year: 2012 (xliv)

Abstract

The upper Gila River Basin in southwestern New Mexico is one of the last unimpounded drainage basins in North America, and is a stronghold for a unique and largely endemic fish fauna. However, coincident with introduction of nonnative predators, such as Smallmouth Bass, Micropterus dolomieu, and Yellow Bullhead, Ameiurus natalis, distributions of native fishes have declined. Reaches with high predator densities could inhibit natural source-sink dynamics of native fishes by disrupting migration and reducing gene flow, thereby isolating local populations and decreasing overall genetic diversity. We used microsatellite DNA markers to examine population structure of seven native species with varying life history strategies and different distributions in the system. Species with opportunistic life history strategies include Spikedace, Meda fulgida, Loach Minnow, Tiaroga cobitis, Speckled Dace, Rhinichthys osculus (species with patchy or limited distributions), and Longfin Dace, Agosia chrysogaster (widespread throughout the basin). Species with periodic life history strategies are Headwater Chub, Gila nigra (limited distribution), Desert Sucker, Catostomus clarkii, and Sonora Sucker, Catostomus insignis (widespread throughout the basin). We collected fin clips from 16 locations representing mainstem and tributaries; however, not all species occurred at each site. Genetic diversity of opportunistic species increased longitudinally upstream to downstream and tests of genetic divergence indicated significant population substructure within the basin. Longfin dace showed the least amount of longitudinal genetic divergence, but more patchily-distributed opportunists exhibited higher divergence values. A canyon-bound reach with high densities of predators was identified to be a substantial barrier to gene flow of opportunistic species. Analyses of periodic species indicated higher genetic diversity at upstream sites than those downstream but no appreciable population substructure. Our comparative genetic study shows that migration and persistence of patchily-distributed opportunistic species will be most strongly affected by anthropogenic and natural factors that limit habitat connectivity in the Gila River.