INVASIVE SPECIES PALEOBIOLOGY: CORBULID BIVALVE PHYLOGENY AND THE FACILITATION OF ECOSYSTEM INVASION

The bivalve family Corbulidae includes about 35 nominal genera of which 15 are extant. Although corbulids are often overlooked in malacologic and paleontologic collections, in part because of their diminutive size, the family is of particular interest biologically and paleontologically because it contains two extant invasive species (Potamocorbula amurensis and Varicorbula gibba), and at least 20 fossil species that came to dominate the freshwater systems they colonized. A better understanding of corbulid evolutionary history is hindered by a number of taxonomic and systematic issues. For example, the generic designation "Corbula" has been applied so widely that it is virtually synonymous with family rank. More significantly, recent phylogenies reconstructed using 18S rRNA genes place Mya arenaria nested within a clade of four corbulid species, calling into question the monophyly of the Corbulidae.

We explore the phylogeny of the Corbulidae using separate and combined analyses of corbulid soft anatomy and shell morphology. Both datasets can yield highly resolved cladograms for molluscs. These datasets may not always complement each other. Often molluscan soft anatomy gives better phylogenetic resolution at higher taxonomic levels whereas shell morphology gives better resolution at lower levels. This study, which builds upon previous research, uses shell characters that describe external ornament, hinge features, pallial line and sinus, and adductor muscle scars. This analysis includes four genera (Notocorbula, Potamocorbula, Anticorbula, and Lentidium) previously uncoded for shell morphology, as well as new outgroups: Mya and Lyonsia. Soft anatomical characters describe all aspects of corbulid anatomy, but focus on more variable features such as the siphons, mantle, gills, muscles, and digestive system. This study presents the first full anatomical descriptions for several corbulid species including P. amurensis, and uses partial dissections to fact-check detailed published anatomical descriptions for other corbulids, including V. gibba. The phylogeny will be used to test hypotheses related to the number of times corbulids have successfully invaded ecosystems and which ecologic and life history characters correlate with these invasions.