Testing alternative vicariance scenarios in Western Mediterranean discoglossid frogs.

Dated molecular phylogenies are often used to interpret evolutionary history with respect to paleogeographic events. Where more than one interpretation is possible, it is desirable but difficult to assess the alternatives in an objective manner. The present work demonstrates a formalized method for testing molecular clock calibrations and biogeographic scenarios based on them. We assessed the plausibility of several previously published biogeographic hypotheses, using the frog genera Alytes, Discoglossus, and Bombina as model groups. Our data set comprised ca. 900bp of partial mitochondrial 16S and 12S rRNA gene sequences (both genes evolved in a clock-like manner across genera) from nearly all the species and subspecies in the three genera. We tested several calibrations of a molecular clock, which resulted in competing temporal settings for the evolution of taxa. Although only one scenario was in complete accordance with paleogeographic data, statistical testing did not reject the alternatives. Limitations encountered with the present approach may be overcome by more comprehensive analyses in future.