Phylogeography of the Wabash pigtoe, Fusconaia flava (Rafinesque, 1820) (Bivalvia: Unionidae)

摘要

Reconstructing the phylogeographic patterns of widely distributed and common freshwater mussel species (Bivalvia: Unionidae) may provide insight into unionid evolution and speciation. The Wabash pigtoe, Fusconaia flava, is currently recognized as a single, polytypic species that is widely distributed and common throughout the Mississippi River drainage and parts of the Canadian Interior, Great Lakes and Gulf Coast drainages. Sequence analysis of the mitochondrial COI gene revealed two divergent (3.43%) clades. Clade A consisted of specimens located throughout the upper and lower Mississippi River drainage and in the Red River (Canada) and Lake Erie drainages and all F. cerina specimens. All haplotypes within clade A differed by three (0.55%) or fewer nucleotide substitutions from the most widely distributed and abundant haplotype, F1. Clade B, consisting of specimens located in the far western portion of the species' range, may comprise an undescribed species. There was no evidence of genetic differentiation among F. flava inhabiting headwater and intermediate-sized river localities of the Muskingum River system and large river localities of the nearby Ohio River. The divergence among F. flava haplotypes comprising clade A (0.18–1.10%) was similar to the divergence between the F. cerina haplotypes and the F. flava haplotypes comprising clade A (0–1.10%). This study illustrates the importance of accessing genetic diversity across the distribution of a polytypic species. Additional analyses based on a combination of morphology and genetics are needed to determine the taxonomic status of clade B and to strengthen our understanding of the relationship between F. flava and F. cerina.