Late Pleistocene lineage divergence among populations ofNeolitsea sericea(Lauraceae) across a deep sea‐barrier in the Ryukyu Islands

Abstract

Aim Our goals were: (1) 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. Location Japan–Ryukyu–Taiwan Island Arc and Chinese/Korean offshore islands. Methods We applied 10 nuclear microsatellites (nSSRs) and one chloroplast (cp) DNA sequence marker (psbA–trnH intergenic spacer) to 31 populations (397 and 326 individuals, respectively) 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 applied to the combined nSSR/cpDNA data set to estimate lineage divergence times and population demographic parameters. Results 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. Main conclusions 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.

Pleistocene glaciations, demographic expansion and subsequent isolation promoted morphological heterogeneity: A phylogeographic study of the alpine Rosa sericea complex (Rosaceae)

“…2). Based on our results, we suspect physical barriers to past or contemporary dispersal (e.g., the Mekong-Salween divide in Hengduan Mountains region for Sinopodophyllum hexandrum 34; the East China Sea/Tsushima-Korean straits for Croomia 35; the Tokara Gap, a deep sea-barrier in the Ryukyu Islands, for Neolitsea sericea 36) have had limited influence on the distributions of the R. sericea . In fact, the relative uniformity among geographic distributions of genotypes suggests sudden demographic expansion, and this type of pattern has been reported recently in Hippuris vulgaris (Plantaginaceae)37, an aquatic herb distributed on the QTP and in adjacent areas.…”

Molecular phylogeography and ecological niche modelling of a widespread herbaceous climber, Tetrastigma hemsleyanum (Vitaceae): insights into Plio–Pleistocene range dynamics of evergreen forest in subtropical China

“…Our data do not allow us to pinpoint these overall rare instances of inter-regional gene exchange to one factor or time; however, they might be associated with contraction/expansion dynamics at rather localized scales during the mid-to-late Pleistocene. The complex topography of subtropical China would have strengthened the phylogeographic structure by limiting gene flow (Qiu et al, 2011), and its breeding system (dioecy) may have imposed additional constraints on gene flow after long-distance dispersal (Rodr ıguez-S anchez et al, 2009;Zhai et al, 2012).…”

Genetic drift drives evolution in the bird-pollinated, terrestrial island endemicGrevillea georgeana(Proteaceae)

“…Populations of species with patchy or discontinuous distributions, such as those on islands, may experience pronounced genetic isolation leading to patterns of deep genetic divergence among populations (Sarthou, Samadi & Boisselier-Dubayle, 2001;Beheregaray et al, 2003;Juan et al, 2004;Barbará et al, 2007;Measey et al, 2007;Zhai et al, 2012). Terrestrial islands, such as granite outcrops and banded iron formations (BIFs), provide particularly interesting study systems, as the matrix between islands may be permeable, resulting in potentially complex spatial and temporal patterns of genetic structure (Masta, 2000;Robin, Sinha & Ramakrishnan, 2010).…”