Molecular phylogenetic analysis of tropical freshwater mussels (Mollusca: Bivalvia: Unionoida) resolves the position of Coelatura and supports a monophyletic Unionidae

Abstract

In previous molecular phylogenetic analyses of the freshwater mussel family Unionidae (Bivalvia: Unionoida), the Afrotropical genus Coelatura had been recovered in various positions, generally indicating a paraphyletic Unionidae. However that result was typically poorly supported and in conflict with morphology-based analyses. We set out to test the phylogenetic position of Coelatura by sampling tropical lineages omitted from previous studies. Forty-one partial 28S nuclear rDNA and partial COI mtDNA sequences (1130 total aligned nucleotides) were analyzed separately and in combination under both maximum parsimony and likelihood, as well as Bayesian inference. There was significant phylogenetic incongruence between the character sets (partition homogeneity test, p < 0.01), but a novel heuristic for comparing bootstrap values among character sets analyzed separately and in combination illustrated that the observed conflict was due to homoplasy rather than separate gene histories. Phylogenetic analyses robustly supported a monophyletic Unionidae, with Coelatura recovered as part of a well-supported Africa–India clade (= Parreysiinae). The implications of this result are discussed in the context of Afrotropical freshwater mussel evolution and the classification of the family Unionidae.