Spotted stream frog diversification at the Australasian faunal zone interface, mainland versus island comparisons, and a test of the Philippine dual umbilici hypothesis

Aim To utilize comprehensive geographical sampling and a new, multilocus dataset to re-examine the biogeography of spotted stream frogs (Hylarana signata complex) throughout Southeast Asia. To compare patterns of diversification among stream frog populations on land-bridge islands and oceanic islands and to re-evaluate a previous ‘dual-invasion’ hypothesis for the origins of endemic Philippine taxa.

Location Southeast Asia, Sundaland, and the Philippines.

Methods We sequenced two mitochondrial and two nuclear gene regions for members of the Hylarana signata complex. We used summary statistics and phylogenetic networks to characterize genetic variation; phylogenetic relationships and ancestral ranges were estimated using Bayesian and likelihood methods. We used the preferred topology and Bayesian methods to evaluate a previous biogeographical ‘dual-invasion’ hypothesis.

Results In contrast to expectations, we found highly divergent, demographically stable and geographically regionalized lineages on the mainland and on land-bridge islands, but minimally divergent, widespread and clinally distributed populations, with evidence of recent demographic expansion, in adjacent oceanic island populations. Novel phylogenetic relationships depart from previous studies and our data strongly reject the previously published ‘dualinvasion’ hypothesis.

Main conclusions Our results join new literature demonstrating that species on mainland and continental shelf islands may harbour high levels of unrecognized diversity, whereas adjacent oceanic island archipelagos can and do support naturally occurring widespread species. Although our data indicate that the individual identities of species previously hypothesized to be involved in the ‘dualinvasion’ scenario may have been incorrect, this mechanism for faunal exchange between the archipelago and adjacent mainland undoubtedly has contributed substantially to the accumulation of endemic vertebrate diversity in the Philippines.