A holistic approach to taxonomic evaluation of two closely related endangered freshwater mussel species, the oyster mussel Epioblasma capsaeformis and tan riffleshell Epioblasma florentina walkeri (Bivalvia: Unionidae) |
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| Authors: | Jones, Jess W. Neves, Richard J. Ahlstedt, Steven A. Hallerman, Eric M. |
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| Affiliation: | 1 U.S. Fish and Wildlife Service, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, U.S.A.; 2 U.S. Geological Survey, Virginia Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, U.S.A.; 3 U.S. Geological Survey, 1820 Midpark Drive, Knoxville, TN 37921, U.S.A.; and 4 Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, U.S.A. |
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| Abstract: | Species in the genus Epioblasma have specialized life historyrequirements and represent the most endangered genus of freshwatermussels (Unionidae) in the world. A genetic characterizationof extant populations of the oyster mussel E. capsaeformis andtan riffleshell E. florentina walkeri sensu late was conductedto assess taxonomic validity and to resolve conservation issuesfor recovery planning. These mussel species exhibit pronouncedphenotypic variation, but were difficult to characterize phylogeneticallyusing DNA sequences. Monophyletic lineages, congruent with phenotypicvariation among species, were obtained only after extensiveanalysis of combined mitochondrial (1396 bp of 16S, cytochrome-b,and ND1) and nuclear (515 bp of ITS-1) DNA sequences. Incontrast, analysis of variation at 10 hypervariable DNA microsatelliteloci showed moderately to highly diverged populations basedon FST and RST values, which ranged from 0.12 to 0.39 and 0.15to 0.71, respectively. Quantitative variation between specieswas observed in fish-host specificity, with transformation successof glochidia of E. capsaeformis significantly greater (P<0.05)on greenside darter Etheostoma blennioides, and that of E. f.walkeri significantly greater (P<0.05) on fantail darterEtheostoma flabellare. Lengths of glochidia differed significantly(P<0.001) among species and populations, with mean sizesranging from 241 to 272 µm. The texture and colourof the mantle-pad of E. capsaeformis sensu stricto is smoothand bluish-white, whereas that of E. f. walkeri is pustuledand brown, with tan mottling. Based on extensive molecular,morphological and life history data, the population of E. capsaeformisfrom the Duck River, Tennessee, USA is proposed as a separatespecies, and the population of E. f. walkeri from Indian Creek,upper Clinch River, Virginia, USA is proposed as a distinctsubspecies. (Received 23 February 2005; accepted 16 January 2006) |
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