LAUSR

The impacts of low-head dams on the genetic structure of small-bodied riverine fishes have not been fully explored. We used both novel and existing microsatellites to assess how 2 low-head dams affect genetic diversity and differentiation in Longear Sunfish (Lepomis megalotis) and Bluntnose Minnow (Pimephales notatus) in an Illinois river system. We expected reduced genetic diversity above dams in both species and greater genetic differentiation in Longear Sunfish, given the species’ more sedentary life history. No detectable patterns of genetic diversity were observed for L. megalotis, whereas a decrease in allelic richness and gene diversity occurred in P. notatus above 1 of the impoundments. The genetic differentiation analyses FST, principal components analysis, and Bayesian clustering revealed that slight genetic differences occurred among some L. megalotis throughout the study area, but these differences were not associated with either dam. In contrast, the same methods showed there were 2 genetically distinct populations of P. notatus separated by 1 of the 2 low-head dams. Our results show that dams do not necessarily impede gene flow or movement of L. megalotis in this region and that small genetic differences are likely the result of the species’ limited home range. However, the strong genetic differentiation we found in P. notatus is probably a result of poor-quality habitat created by a dam that restricts P. notatus movement. Our data show that even small dams can influence genetic structure in river systems but that they affect species in different ways that are not necessarily intuitive based on the life history of a species.