Impact of the Mid-Pleistocene Revolution and Anthropogenic Factors on the Dispersion of Asian Black-Spined Toads (Duttaphrynus melanostictus)

SIMPLE SUMMARY: Three distinct lineages of Duttaphrynus melanostictus, the Asian black-spined toad, are present in Southeast Asia. However, divergence times, dispersion mechanisms and colonisation processes are still unknown. In the present study, molecular dating based on mitochondrial DNA sequences demonstrated that D. melanostictus expanded into Eastern Indomalaya following the Quaternary glaciation and colonised new landscapes during the Last Glacial Maximum. Subsequent to natural colonisation of landscapes, we found human-induced dispersal into regions such as in Taiwan, Southern Sundaic and Wallacea, temporally matching with prehistoric human settlements. We provide comprehensive dispersal pathways and mechanisms of D. melanostictus to the Eastern Indomalayan realm, thus solving the climate-driven question relevant to the species distribution in the Southeast Asia. ABSTRACT: Divergence-time estimation critically improves the understanding of biogeography processes underlying the distribution of species, especially when fossil data is not available. We hypothesise that the Asian black-spined toad, Duttaphrynus melanostictus, expanded into the Eastern Indomalaya following the Quaternary glaciations with the subsequent colonisation of new landscapes during the Last Glacial Maximum. Divergence dating inferred from 364 sequences of mitochondrial tRNAGly ND3 supported the emergence of a common ancestor to the three D. melanostictus clades around 1.85 (±0.77) Ma, matching with the Lower to Mid-Pleistocene transition. Duttaphrynus melanostictus then dispersed into Southeast Asia from the central Indo-Pacific and became isolated in the Southern Sundaic and Wallacea regions 1.43 (±0.10) Ma through vicariance as a result of sea level oscillations. The clade on the Southeast Asian mainland then colonised the peninsula from Myanmar to Vietnam and expanded towards Southeastern China at the end of the Mid-Pleistocene Revolution 0.84 (±0.32) Ma. Population dynamics further highlight an expansion of the Southeast Asian mainland population towards Taiwan, the Northeastern edge of the species’ range after the last interglacial, and during the emergence of the Holocene human settlements around 7000 BP. Thus, the current divergence of D. melanostictus into three segregated clades was mostly shaped by Quaternary glaciations, followed by natural dispersion events over land bridges and accelerated by anthropogenic activities.