The Phylogeography Of Neolitsea Sericea,an Island Endemic And Endangered Plant In East Asia

Neolitsea sericea (B1.) Koitz. (Lauraceae) is an element in the dioecious, warm-temperate evergreen forests, which is distributed from Taiwan (Orchid Island), through the Ryukyus to southern Japan, but also occurs disjunctively in off-shore islands of both East China (Zhoushan Archipelago) and South Korea (Jeju Island). A phylogeographic study of Neolitsea sericea was conducted:(i) to assess the population genetic structure and demographic divergence history of a bird-dispersed tree, Neolitsea sericea, endemic to East Asian land-bridge islands; and (2) to interpret the results in the light of controversies over the dating and configurations of land bridges through the Japanese Ryukyu Island Arc.We applied ten nuclear microsatellites (nSSRs) and one chloroplast (cp) DNA sequence marker (psbA-trnH intergenic spacer) to 31 populations from throughout the species’range to infer current patterns of genetic diversity and structure, and pollen-to-seed migration ratios (r). A coalescent-based isolation-with-migration (IM) model was fitted to the combined nSSR/cpDNA data set to estimate lineage divergence time and population demographic parameters.The geographic structure of nSSRs and the distribution of most cpDNA haplotypes revealed two distinct lineages located in areas north and south of the ’Tokara Gap’, a narrow (c.37 km wide) but deep (> 1000 m) sea-strait between the northern and central Ryukyus. Based on the IM analyses, we (1) dated the divergence of these northern and southern lineages to c.0.07 Ma (90% highest posterior density interval:0.02-0.38 Ma); (2) estimated a slightly smaller effective population size for the northern compared to the southern lineage; and (3) recovered only trivial signals of post-divergence gene flow between them.The estimated divergence time for northern and southern lineages is consistent with geological evidence for the existence of land connections in the Tokara region during cold stages of the latest Pleistocene; it is thus incompatible with an’ancient sea-barrier hypothesis’for the Ryukyu Arc, where we would have expected much older divergences related to the initial formation of the Tokara and Kerama tectonic straits during the Pliocene. Multiple factors are likely to have had a role in the divergence of N. sericea, including not only land-bridge submergence, but also island configuration, and/ or constraints on adaptation along a latitudinal temperature gradient.