DNA adds some 'mussel' to conservation efforts


The Southeastern United States is a center for biodiversity in North America. This is particularly true for freshwater mussels. The Ohio Valley is home to numerous species of freshwater mussels (family: Unionidae; class: Bivalvia) and the upper Coosa River basin in Tennessee, Georgia and Alabama was once home to over 40 species of freshwater mussels making it among the most biologically diverse freshwater habitats on Earth. Unfortunately, however, human activity in the great watersheds of the Southeast have had devastating effects on freshwater mussel diversity. The building of locks and dams, agricultural and industrial run-off and urbanization along rivers have all contributed to the extinction of many species of freshwater mussel. In the Ohio valley species like the Clubshell (Pleurobema clava, see photo left) exist in populations that are considered highly vulnerable to extinction and other species, like the Tubercled Blossum (Epioblasma torulosa, see photo bottom right, both specimens are from the Cincinnati Museum Center Zoology collection), are likely extinct already. For freshwater mollusks in general over 70% of the known species are extinct or in danger of extinction.

Identifying one mussel species from another can however be difficult. Mussels are typically identified on the basis of the size, shape and texture of their shells, however, within populations these traits can vary significantly and often vary in response to variation in the environment. The difficulty in identifying one species from another confounds conservation efforts to identify threatened populations and leaves open the possibility that species thought to be extinct may persist in populations with aberrant characteristics making them difficult to distinguish from more common species.

In a recent paper by University of Alabama researcher David Campbell and his colleagues, DNA barcoding was used as a tool in identifying freshwater mussel species in the Coosa basin. DNA barcoding involves sequencing a segment of DNA common to all organisms. In general, sequences should be unique to a species, although there is often some sequence variation within species as well. DNA barcodes can be used in addition to analysis of morphological characteristics as a tool in identifying species. Focusing on the freshwater mussel genus Pleurobema, DNA barcoding revealed the existence of four species thought to be extinct from the Coosa basin; Pleurobema chattanoogaese, P. hanleyianum, P. troschelianum, and P. stabile. The DNA evidence showed that all of the Coosa basin specimens previously identified as Peurobema perovatum were actually the supposedly extinct P. hanleyianum. Also, the Warrior Pigtoe (Pleurobema rubellum), a mussel species currently listed as extinct, was identified using DNA barcoding from the nearby Black Warrior River system.

This study shows the utility of DNA analyses in conservation efforts. With the growing emphasis on DNA techniques here at Cincinnati Museum Center plans are underway to adopt DNA barcoding protocols on threatened and difficult to identify groups, like freshwater mussels, in the Ohio Valley.

CAMPBELL, D.C., JOHNSON, P.D., WILLIAMS, J.D., RINDSBERG, A.K., SERB, J.M., SMALL, K.K., LYDEARD, C. (2008). Identification of ‘extinct’ freshwater mussel species using DNA barcoding. Molecular Ecology Resources DOI: 10.1111/j.1755-0998.2008.02108.x