Phylogenetic relationships and genetic diversity of the Polypedates leucomystax complex in Thailand

Controversy in the taxonomic evaluation of the Asian tree frog Polypedates leucomystax complex presents the challenging task of gaining insight into its biogeographical distribution and diversification. Here, we describe the dispersion and genetic relationship of these species in Thailand where we connect the population of the P. leucomystax complex of the Sunda Islands to the mainland population based on the mitochondrial cytochrome c oxidase subunit I ( COI ) gene, derived from 266 samples. Our maternal genealogy implies that there are four well-supported lineages in Thailand, consisting of Northern A (clade A: Polypedates sp.), Nan (clade B: P. cf. impresus ), Southern (clade C: P . cf. leucomystax ) and Northern B (clade D: P. cf. megacephalus ), with Bayesian posterior probability >0.9. Phylogeny and haplotype networks indicate that clades A, B and D are sympatric. In contrast, clade C ( P . cf. leucomystax ) and clade D ( P. cf. megacephalus ) are genetically divergent due to the geographical barrier of the Isthmus of Kra, resulting in allopatric distribution. Climatic conditions, in particular rainfall, that differ on each side of the Isthmus of Kra may play an important role in limiting the immigration of both clades. For the within-populations of either clades C or D, there was no significant correlation between geographic and genetic distance by the isolation-by-distance test, indicating intraspecific gene flow of each clade. Population expansion occurred in clade C, whereas clade D showed a constant population. Taken together, the P. leucomystax complex in Southeast Asia may be diversified by climatic oscillation, leading to allopatric and/or sympatric speciation.