A family-level Tree of Life for bivalves based on a Sanger-sequencing approach.

The systematics of the molluscan class Bivalvia are explored using a 5-gene Sanger-based approach including the largest taxon sampling to date, encompassing 219 ingroup species spanning 93 (or 82%) of the 113 currently accepted bivalve families. This study was designed to populate the bivalve Tree of Life at the family level and to place many genera into a clear phylogenetic context, but also pointing to several major clades where taxonomic work is sorely needed. Despite not recovering monophyly of Bivalvia or Protobranchia-as in most previous Sanger-based approaches to bivalve phylogeny-our study provides increased resolution in many higher-level clades, and supports the monophyly of Autobranchia, Pteriomorphia, Heteroconchia, Palaeoheterodonta, Heterodonta, Archiheterodonta, Euheterodonta, Anomalodesmata, Imparidentia, and Neoheterodontei, in addition to many other lower clades. However, deep nodes within some of these clades, especially Pteriomorphia and Imparidentia, could not be resolved with confidence. In addition, many families are not supported, and several are supported as non-monophyletic, including Malletiidae, Nuculanidae, Yoldiidae, Malleidae, Pteriidae, Arcidae, Propeamussiidae, Iridinidae, Carditidae, Myochamidae, Lyonsiidae, Pandoridae, Montacutidae, Galeommatidae, Tellinidae, Semelidae, Psammobiidae, Donacidae, Mactridae, and Cyrenidae; Veneridae is paraphyletic with respect to Chamidae, although this result appears to be an artifact. The denser sampling however allowed testing specific placement of species, showing, for example, that the unusual Australian Plebidonax deltoides is not a member of Donacidae and instead nests within Psammobiidae, suggesting that major revision of Tellinoidea may be required. We also showed that Cleidothaerus is sister group to the cementing member of Myochamidae, suggesting that Cleidothaeridae may not be a valid family and that cementation in Cleidothaerus and Myochama may have had a single origin. These results highlight the need for an integrative approach including as many genera as possible, and that the monophyly and relationships of many families require detailed reassessment. NGS approaches may be able to resolve the most recalcitrant nodes in the near future.

Molecular phylogenetic analysis supports a Gondwanan origin of the Hyriidae (Mollusca: Bivalvia: Unionida) and the paraphyly of Australasian taxa.

The freshwater mussel family Hyriidae (Mollusca: Bivalvia: Unionida) has a disjunct trans-Pacific distribution in Australasia and South America. Previous phylogenetic analyses have estimated the evolutionary relationships of the family and the major infra-familial taxa (Velesunioninae and Hyriinae: Hyridellini in Australia; Hyriinae: Hyriini, Castaliini, and Rhipidodontini in South America), but taxon and character sampling have been too incomplete to support a predictive classification or allow testing of biogeographical hypotheses. We sampled 30 freshwater mussel individuals representing the aforementioned hyriid taxa, as well as outgroup species representing the five other freshwater mussel families and their marine sister group (order Trigoniida). Our ingroup included representatives of all Australian genera. Phylogenetic relationships were estimated from three gene fragments (nuclear 28S, COI and 16S mtDNA) using maximum parsimony, maximum likelihood, and Bayesian inference, and we applied a Bayesian relaxed clock model calibrated with fossil dates to estimate node ages. Our analyses found good support for monophyly of the Hyriidae and the subfamilies and tribes, as well as the paraphyly of the Australasian taxa (Velesunioninae, (Hyridellini, (Rhipidodontini, (Castaliini, Hyriini)))). The Hyriidae was recovered as sister to a clade comprised of all other Recent freshwater mussel families. Our molecular date estimation supported Cretaceous origins of the major hyriid clades, pre-dating the Tertiary isolation of South America from Antarctica/Australia. We hypothesize that early diversification of the Hyriidae was driven by terrestrial barriers on Gondwana rather than marine barriers following disintegration of the super-continent.

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

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.