In situ glacial survival at the northern limit of tropical insular Asia by a lowland herb Begonia fenicis (Begoniaceae)

Equatorward contraction and re-expansion during and after the last glacial maximum has been reported for temperate plants, but little is known about latitudinal shifts of tropical plants in insular Asia. We used molecular methods to test the post-glacial migration hypothesis for Begonia fenicis at the northern limit of tropical insular Asia, namely, the northern Philippines, southern Taiwan and the southern Ryukyus of Japan. Based on internal transcribed spacer sequences, analyses of phylogeographical structure suggested long-term survival of island populations and negated recent northward migration; demographic analyses indicated spatial expansion in the early Pleistocene and subsequent stable demography. Based on nuclear microsatellites, Bayesian clustering and other spatial analyses indicated inter-island differentiation, and coalescent analysis of migration indicated the lack of inter-island migration during and after the last glacial maximum. Our results refuted the postglacial migration hypothesis for B. fenicis and suggest in situ survival through the last glacial maximum. The stable historical distribution and demography are probably attributable to the Kuroshio Current bringing warm and humid air, which washed these islands even during the glacial periods. Additionally, because these are low islands, absence of competition with montane plants descending to the lowlands during cooler periods may have mitigated the influence of temperature lowering and facilitated their survival. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 305–325.