Genetic characterization of the clubshell species complex (Pleurobema clava and P. oviforme) for enhanced conservation

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The diversity of freshwater mussels (family Unionidae) in the United States is unmatched in the rest of the world, yet this biodiversity is highly vulnerable, with more than 70% of recognized species considered to be either endangered, threatened, or of special concern.  Most species inhabit limited ranges and have small (and/or often unknown) dispersal abilities due to reliance on specific host fish for reproduction, making them easily fragmented and particularly susceptible to the activities of humans, such as habitat modification, pollution, and over-harvesting.

 

Species in the genus Pleurobema are difficult to distinguish because of shell similarities and shapes that may vary with age and ecological conditions within species. As such, molecular tools have proven useful as a supplement to traditional, morphology-based taxonomic methods. Recent genetic analyses have indicated that the ESA petitioned Tennessee clubshell (Pleurobema oviforme) and the federally endangered clubshell (Pleurobema clava) are very closely related and may not represent distinct species. Historically, the clubshell was abundant throughout the Ohio River drainage in seven states, including the Allegheny River in Pennsylvania, which now supports the largest reproducing population. The status of the remaining known P. clava populations is uncertain and several face threats to their continued existence. The Tennessee clubshell is considered endemic to the Cumberlandian region but appears to be imperiled in the Cumberland River system. Populations of Tennessee clubshell in the Upper Tennessee River basin appear more stable.

Effective conservation and restoration plans require clearly definable units of management. In this study we are employing a suite of molecular tools (i.e., mitochondrial DNA haplotype analysis and mitochondrial genome sequencing, nuclear DNA microsatellites, and next-generation sequencing technologies) to resolve species boundaries. Our species- and population-level evaluations will inform managers facing listing decisions for ‘at-risk’ species and aid in the recovery of currently listed species. If the Tennessee clubshell and clubshell are determined to be the same species, ESA protection may not be warranted for the Tennessee clubshell and status and recovery strategies may need to be re-evaluated for the clubshell.

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Dr. Nathan Johnson takes a non-invasive tissue sample of a freshwater mussel at the Green River, Kentucky

Dr. Nathan Johnson takes a non-invasive tissue sample of a freshwater mussel at the Green River, Kentucky.

(Credit: Cheryl Morrison, USGS Leetown Science Center. Public domain.)

The clubshell, Pleurobema clava, from the Allegheny River, Pennsylvania

The clubshell, Pleurobema clava, from the Allegheny River, Pennsylvania

(Credit: Cheryl Morrison, USGS Leetown Science Center. Public domain.)