Patterns of genetic structure in the endangered aquatic gastropodValvata utahensis(Mollusca: Valvatidae) at small and large spatial scales

Abstract

Summary1. The aquatic snailValvata utahensis(Gastropoda: Valvatidae) is a federally endangered aquatic mollusk known only from the Snake River in southern Idaho, U.S.A. The Snake River, like many other large river systems in the western United States, has undergone substantial anthropogenic modifications in recent history that have altered water flows, changed physicochemical attributes of the water and produced an overall spatially fragmented aquatic system.2. Because little is currently known about the basic biology and life history ofV. utahensis, we conducted a detailed genetic analysis of amplified fragment length polymorphism (AFLP) and mitochondrial DNA sequence variation in this species from six locations along the Snake River. This study was designed to discern (i) levels of within‐location genetic diversity, (ii) patterns of genetic structure at small spatial scales (i.e. within sampling locations) and (iii) patterns of genetic structure at large spatial scales (among sampling locations).3. We show that comparable levels of nuclear genetic variation exist within each of the six locations examined. However, reduced mitochondrial sequence diversity was observed at Thousand Springs compared with the other locations examined.4. We further illustrate thatV. utahensisshows no genetic structure within locations over relatively small physical distances up to approximately 3 km. We suggest that active dispersal of individuals via crawling and passive dispersal because of downstream displacement or floating behaviours may have produced this pattern. However, at large spatial scales genetic structure generally followed an isolation‐by‐distance pattern. This pattern was not directly correlated with the connectivity of locations through the river corridor and suggested the possible role of episodic passive dispersal via avian waterfowl or the effects of historical floods throughout the Snake Riverc.14 000 years ago.