Mapping aquatic faunal exchanges across the Sunda shelf,South-East Asia,using distributional and genetic data sets from the cyprinid fish Barbodes gonionotus (Bleeker, 1850)

The islands of Sumatra, Java and Borneo and mainland South-East Asia are encompassed by a shallow marine shelf, the Sunda shelf. The striking faunal similarities between countries bordering the Sunda shelf have been attributed to faunal exchanges across the shelf during Pleistocene glacial maxima when sea levels fell by up to 120 m and the shelf was exposed and drained by large river systems which connected many of today's rivers. The widespread distribution of fish species reflecting extensive faunal exchange across the area is predicted to be observed within species through the broad geographic distribution of genetic lineages. Here I report a discontinuous species distribution across the region for the cyprinid fish, Barbodes gonionotus. Mitochondrial DNA control region sequence and nuclear locus data from populations sampled across the species range, suggest that the present species distribution largely reflects faunal exchanges early in the Pleistocene and that these two regional population groupings have subsequently diverged in isolation. However, the mtDNA data present some evidence for limited genetic dispersal during more recent Pleistocene low sea levels. These results broadly confirm previous work from a catfish species and suggest that freshwater faunal exchanges may have been limited across the region during the Pleistocene despite extended periods during which the Sunda shelf was exposed.