Brooding in Corbicula madagascariensis (Bivalvia, Corbiculidae) and the repeated evolution of viviparity in corbiculids

摘要

The limnic bivalve genus Corbicula Megerle von Muhlfeld, 1811 is a hyper-invasive neozoon in North and South America as well as in Europe, where currently some taxa are rapidly extending their range. In addition to its extraordinarily invasive potential, the 'Asiatic clam' is remarkable for its recently discovered wide spectrum of reproductive strategies comprising oviparity, ovoviviparity and euviviparity. It renders Corbicula an ideal model for studying evolutionary transformations of reproductive features, in particular with respect to intrabranchial incubation (brooding) of embryos and shelled larvae in freshwater lineages. Based on rare material from Madagascar we here present evidence for prolonged incubation interpreted as being indicative of euviviparous reproduction in C. madagascariensis Smith, 1882. This mode is not only novel for corbiculids from the Ethiopian biogeographical region, but suggests - in combination with a mtDNA phylogeny - a more complicated pattern of the evolution of reproductive modes in corbiculids than previously assumed. We find an independent origin of viviparity and even euviviparity in the South American Neocorbicula Fischer, 1887 and the Afro-Asian Corbicula, representing a remarkable example of parallel evolution in New and Old World corbiculids.