Diffusion of nuclear and mitochondrial genes across a zone of secondary contact in the maritime shrew, Sorex maritimensis: implications for the conservation of a Canadian endemic mammal

mtDNA and AFLP markers demonstrate limited genetic differentiation within the Pyganodon cataracta–Pyganodon fragilis freshwater mussel complex in Atlantic Canada

Two nominal species of freshwater mussels, Pyganodon cataracta (Say, 1817) (eastern floater) and Pyganodon fragilis (Lamarck, 1819) (Newfoundland floater), occur in Atlantic Canada, but their taxonomic status has been controversial. We analyzed the female-transmitted mitochondrial cytochrome c oxidase subunit I (i.e., FCOI) and nuclear internal transcribed spacer region (ITS-1) gene sequences, as well as multilocus amplified fragment length polymorphism (AFLP) markers, to evaluate genetic variation in Pyganodon specimens from Atlantic Canada. We found that Pyganodon samples from this region displayed no or extremely low (i.e., <0.5%) genetic divergence for ITS-1 and FCOI sequence data, respectively. Inferences from nested clade analysis of FCOI haplotypes suggest restricted gene flow with isolation by distance and contiguous range expansion. Analysis of molecular variance inferred from presence or absence of nuclear-encoded AFLP bands showed moderate geographic structuring among provinces but no correspondence between mtDNA haplotypes and AFLP profiles. Similarly, there was no correspondence between presence of a single or a double loop on the umbo and FCOI haplotype. These mtDNA and AFLP markers demonstrate limited genetic differentiation within the Pyganodon cataracta–Pyganodon fragilis freshwater mussel complex in Atlantic Canada and question the species-level distinctness of these putative taxa.