First Name:
Erin
Last Name:
Abernathy
Major Department:
Biology
Thesis Director:
Mike Gangloff
Date of Thesis:
May 2011
Freshwater mussels are a vital component of stream ecosystems in the Southeastern United States. Of the 270 species that are found in this region, 70% are imperiled. While the causes of freshwater mussel declines at broad spatial scales are not well understood, dams are suspected to be a major factor in regional and local declines. Dams affect stream physiochemical habitat conditions and form barriers to migration, potentially restricting gene flow between populations. Surprisingly, few studies have examined the effects of dams on freshwater mussel population genetics. I examined the genetic structure of a freshwater mussel (Elliptio arca) population occurring in a small stream with a historic mill dam. I predicted that this dam should pose a significant barrier to mussel population gene flow by acting as a barrier to host fish. Restriction of host fish-mediated mussel dispersal across the dam and the reservoir should result in haplotype segregation and low gene flow between populations up and downstream of the dam. I examined the haplotype distribution using the mitochondrial NADH1 gene for 48 mussels from Sandy Creek, Alabama. Mussels were collected from sites up and downstream of Jones Mill Dam, a structure dating to the 1840s. I found unique haplotypes up and downstream from the dam, suggesting that population structuring may be occurring. High gene flow (Nm = 4.09) and interbreeding parameters (Fst = 0.05765) indicate that Jones Mill Dam may not be a complete barrier to downstream migration, but the presence of unique haplotypes downstream of the dam indicate that upstream exchange of genetic material may be restricted.
Comparison of E. arca specimens from Sandy Creek to published Genbank sequences indicates a substantial degree of genetic differentiation (~4.0% from both putative conspecifics and other Elliptio taxa) that is consistent with interspecific divergence. Intra-3 population genetic diversity is low, suggesting that these individuals may represent a previously un-recognized toxon endemic to the upper Tallapoosa River Drainage. Additional surveys and sequencing are needed in order to fully describe the range of this species, assess its conservation status, and its relationship to other Elliptio taxa. The influence of the dam is not entirely clear, but there is some evidence that it may act as a barrier to upstream gene flow. Genetic diversity up and downstream of the dam was similar, so it does not appear that Jones Mill Dam is increasing the likelihood that mussels upstream of the dam will be extirpated. Additional data from an adjacent, un-impounded reach of Sandy Creek will provide evidence to link haplotype distributions to dam effects or natural genetic variation.