Genetic Structure of Creek Chub, a Headwater Minnow, in an Impounded River System

Abstract

The population-level effects of landscape heterogeneity in migration corridors are not well understood, especially in aquatic ecosystems. Using 17 microsatellite loci, we assessed the spatial genetic structure of creek chub Semotilus atromaculatus, a headwater stream fish, in eight small tributaries (202 individuals) connected by a river (a lotic corridor) and eight small tributaries (200 individuals) connected by a nearby downstream reservoir (a lentic corridor). Genetic diversity measured in terms of gene diversity and allelic richness was higher in the river tributaries than reservoir tributaries. Both the river and reservoir tributaries exhibited significant population differentiation but differed in their patterns of isolation by distance. Pairs of river tributaries showed increasing genetic differentiation with increasing geographic distance, whereas reservoir tributaries showed no effect of geographic distance on genetic distance. Bayesian estimates of gene flow showed a trend of higher recent migration among river tributaries than reservoir tributaries, but the difference was not statistically significant. Our results may indicate an association between one feature of the aquatic landscape's structure (i.e., whether a connecting water body and migration corridor is riverine or reservoir in type) and population genetic structure in a headwater stream fish. Accordingly, additional genetic studies of populations inhabiting tributaries of river-reservoir networks in other watersheds are needed to further assess this possibility.