GEODISPERSAL VERSUS VICARIANCE IN THE HISTORY OF CORBULID BIVALVES: IS THERE A LINK BETWEEN BIOGEOGRAPHIC ORIGIN AND INVASIVENESS?

The Corbulidae are a diverse (35 genera) and long-lived (Jurassic-Recent) clade of marine to freshwater bivalves with both extant and extinct invasive species. The two extant invasive species (Potamocorbula amurensis and Varicorbula gibba) dispersed via transcontinental jumps (Asia to North America and Europe to Australia, respectively) attributed to ballast water transport. In contrast, invasions by several corbulid subclades into freshwater ecosystems, as recorded in the fossil record, appear to occur via range expansion from proximal marine and/or brackish populations, followed by speciation.

Here, we use a revised phylogenetic analysis of the Corbulidae (including both shell and soft anatomic characters, and both extinct and extant taxa) with modified Brooks parsimony analysis to reconstruct the history of geodispersal and vicariance within the clade, and examine the potential link between biogeographic origin and invasiveness. Results suggest that basal splits in the Corbulidae are dominated by geodispersal, whereas the distal splits are dominated by vicariance. Further, both modern invasive species and most fossil freshwater invaders tend to be basal within the phylogeny, suggesting a link between the origin of these subclades via geodispersal and the presence of invasive species, whether the invasion occurs via geographic jumps to similar environments or expansion into new ecosystems. However, our results also document instances where clades originating through geodispersal have not become invasives (i.e., Bicorbula gallica and Lentidium mediterraneum), but no instances of invaders that originated through vicariance. These results suggest that origination via geodispersal is only a component of invasive potential and that other ecologic traits, such as the potential to be ecosystem engineers or wide environmental tolerances, also are critical to invasive success.