Nine families of bivalve molluscs have undergone successful radiations in freshwater habitats, including three heterodont taxa: the Sphaeriidae, Corbiculidae, and Dreissenidae. Although the phylogenetic relationships of these freshwater heterodont families are controversial, most workers place the first two in the superfamily Corbiculoidea and assume that they represent a monophyletic grouping. We have tested competing phylogenetic hypotheses for the Corbiculoidea by constructing a representative molecular phylogeny, based on domains D1-D3 of the nuclear large subunit 28S rDNA, for 18 heterodont bivalves and for two oyster outgroup taxa. Our results do not support the monophyly of the Corbiculoidea and are consistent with the hypothesis that all three families of freshwater heterodonts represent independent colonization events by marine ancestors. Similarities in developmental mode specializations exhibited by some sphaeriids and corbiculids, such as sequential direct-developing broods, represent convergent adaptations to the freshwater environment. The corbiculid taxa form a clade with venerid and mactrid outgroups but we were not able to identify a putative marine outgroup for the sphaeriids. (C) 2000 Academic Press.
Bibliographical noteFunding Information:
We thank Dr. B. L. Choe, D. Marelli, S. Allen, V. Kennedy, C. Ituarte, T. Lee, G. Paulay, L. Cooley, and R. Sherman for providing specimens. J. Megahan kindly drew the shells and D. Graf, L. Cooley, and J. Burch reviewed early drafts. We also thank two anonymous reviewers for their constructive comments. This study was supported by a KOSEF (Korea Science and Engineering Foundation) Postdoctoral Research Grant to J.-K. Park and by NSF Award 9617689 to D. Ó Foighil.
- 28S rDNA
- Freshwater heterodont bivalves
- Molecular phylogeny