Incongruent genetic population structure between a unionid and its host fish

The movement and distribution of unionid mussels is largely a result of movement by their host fish. Recent research has discovered that Epioblasma triquetra, Snuffbox mussel (Unionidae) and other congeners use a fascinating fish trapping behavior to parasitize a potential host. Of particular interest is that darter species other than the logperch (Percina caprodes), trapped by the Snuffbox would not survive the trapping behavior. This made the logperch-Snuffbox relationship an ideal candidate system for a co-evolutionary study. Following co-evolutionary theory, we hypothesized that the population genetic structure of Snuffbox (assessed in a previous study) should closely match that of its host. Using Mantel tests (pairwise genetic distance matrices) and genetic assignment tests (STRUCTURE) on microsatellite DNA data, we found that the genetic population structures of parasite and host were incongruent. This means that logperch are likely not the sole host for the Snuffbox and are not entirely responsible for the genetic population structure observed for Snuffbox. Our results suggest, that another host (possibly blackside darter, Percina maculata) may be responsible for the population structure in combination with the specialized ecological preferences (riffle specialist) and limited mobility of Snuffbox. Management implications of these findings for the imperiled Snuffbox will be discussed.