SREL Reprint #2135

Molecular systematics and evolution of reproductive traits of North American freshwater unionacean mussels (Mollusca: Bivalvia) as inferred from 16S rRNA gene sequences

Charles Lydeard1, Margaret Mulvey2, and George M. Davis3

1Aquatic Biology Program, Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487, USA
2Savannah River Ecology Laboratory, P.O. Drawer E, Aiken, SC 29802, USA
3Academy of Natural Sciences of Philadelphia, Nineteenth and the Parkway, Philadelphia, PA 19103, USA

Abstract: North American freshwater unionacean bivalves are a diverse group of nearly 300 species. Unionaceans exhibit an array of conchological, anatomical, life history, and reproductive characteristics that have figured prominently in proposed classification schemes. Recently, two very different classifications of North American unionaceans have been proposed. Depending on the classification system utilized, a very different evolutionary trajectory of anatomical and reproductive features is obtained. The lack of a robust, well corroborated phylogeny of North American unionacean bivalves hinders the progress of evolutionary and ecological studies involving these species. Here we present a mitochondrial DNA (mtDNA) based phylogeny for North American unionaccan mussels and compare it to previously proposed classifications. In addition, we present a 'total evidence' phylogeny which incorporates both the mtDNA sequence data and available morphological data. The molecular and total evidence phylogenies agree largely with the conclusions of a previous study based largely on immunoelectrophoretic data. North American unionaceans can be divided into two families: the Unionidae, which is comprised of most of the species and the Margaritiferidae. Within the Unionidae are two subfamilies, the Anodontinae and Ambleminae. The resultant phylogeny was used to examine the evolution of several key anatomical features including the number of gills (demibranchs) used by females to brood developing embryos, incubation length (bradytictic vs tachytictic), larval (glochidial) tooth structures, and shell texture. Both molecular and total evidence phylogenies indicate several of the aforementioned characters evolved independently or were subsequently lost or gained in several lineages.

SREL Reprint #2135

Lydeard, C., M. Mulvey, and G.M. Davis. 1996. Molecular systematics and evolution of reproductive traits of North American freshwater unionacean mussels (Mollusca: Bivalvia) as inferred from 16S rRNA gene sequences. The Royal Society (London) Series B 351:1593-1603.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).