Phylogeographic Patterns Among The Freshwater Mussel Elliptio lanceolate Species Complex

Integration of molecular, morphological and biogeographic data improves our ability to elucidate species boundaries and phylogenetic relationships. Extreme morphological variation among freshwater mussel Elliptio species has led to the proliferation of species names and debate about the phylogenetic structure within this genus. Earlier studies have considered Elliptio to be comprised of three species complexes; current species lists recognize seven taxa in the lanceolate complex. I examined phylogenetic relationships within the lanceolate Elliptio complex from 20 Atlantic Slope river basins using mitochondrial (COI and NDI) and nuclear (ITS-1 and 28S) DNA sequences. I constructed haplotype networks to examine species boundaries, biogeographic trends of gene exchange and to guide my single and multi gene phylogenetic analyses. My data revealed three taxa in the lanceolate Elliptio complex. E. lanceolata was recovered as monotypic and highly divergent from the core Elliptio group (E. complanata and related taxa). I found support for two morphologically distinct and genetically divergent lineages, a northern E. fisheriana and a southern E. angustata lance clade that are more closely related to the core Elliptio group than the E. lanceolata taxa. Future steps are to revise taxonomy and provide guidance to resource managers tasked with managing this imperiled group of organisms.