Flying to the beat of a different drum: discordant patterns of butterfly dispersal across the Indo-Australian archipelago

The Indo-Australian Archipelago comprises over 20,000 islands from countries including Indonesia, Malaysia, and the Philippines. Tectonic forces and eustasy drove changes in the configuration of its landmasses and seas throughout the Cenozoic. We predicted that widespread butterfly species co-distributed throughout the region would show concordant patterns of genetic differentiation.  Specifically, we hypothesized that phylogenetic structure would result from past or present geographic isolation as demarcated by: 1) Wallace’s Line; 2) the Miocene “Savannah Corridor” separating forests on the eastern and western Sunda shelf; 3) the Sunda Strait between Java and Sumatra; and 4) Huxley’s Line between Palawan and the rest of the Philippines. We sequenced 1,825 bp of mitochondrial DNA from over 400 specimens representing seven butterfly species in three families collected from every major landmass where they occur.  Bayesian and parsimony trees provide some evidence for the geographic patterns we predicted.  To determine whether species with similar population structure experienced simultaneous divergence, we used methods incorporating Approximate Bayesian Computation, which takes into account the stochasticity of genetic coalescence. We find each of our hypothesized patterns in some but not all species, suggesting that common geographic barriers have caused isolation within some lineages. It is likely that each species has diverged independently, through asynchronous dispersal events.