A strong ‘filter’ effect of the East China Sea land bridge for East Asia’s temperate plant species: inferences from molecular phylogeography and ecological niche modelling of Platycrater arguta(Hydrangeaceae)

Abstract

BackgroundIn East Asia, an increasing number of studies on temperate forest tree species find evidence for migration and gene exchange across the East China Sea (ECS) land bridge up until the last glacial maximum (LGM). However, it is less clear when and how lineages diverged in this region, whether in full isolation or in the face of post-divergence gene flow. Here, we investigate the effects of Quaternary changes in climate and sea level on the evolutionary and demographic history of Platycrater arguta, a rare temperate understorey shrub with disjunct distributions in East China (var. sinensis) and South Japan (var. arguta). Molecular data were obtained from 14 P. arguta populations to infer current patterns of molecular structure and diversity in relation to past (Last Interglacial and Last Glacial Maximum) and present distributions based on ecological niche modelling (ENM). A coalescent-based isolation-with-migration (IM) model was used to estimate lineage divergence times and population demographic parameters.ResultsCombining information from nuclear/chloroplast sequence data with nuclear microsatellites, our IM analyses identify the two varieties as genetically distinct units that evolved in strict allopatry since the mid-Pleistocene, c. 0.89 (0.51–1.2) Ma. Together with Bayesian Skyeline Plots, our data further suggest that both lineages experienced post-divergence demographic growth, followed by refugial isolation, divergence, and in the case of var. arguta post-glacial admixture. However, past species distribution modelling indicates that the species’ overall distribution has not greatly changed over the last glacial cycles.ConclusionsOur findings highlight the important influence of ancient sea-level changes on the diversification of East Asia’s temperate flora. Implicitly, they challenge the notion of general temperate forest expansion across the ECS land bridge, demonstrating instead its ‘filter’ effect owing to an unsuitable environment for certain species and their biological (e.g., recruitment) properties.

Molecular Phylogeny and Biogeographic Diversification of Linnaeoideae (Caprifoliaceae s. l.) Disjunctly Distributed in Eurasia, North America and Mexico

“…The East China Sea Land Bridge [90, 91] may have allowed dispersal and gene exchange between woodland species of East China, Korea and Japan. Examples such as Cercidiphyllum japonicum [88] and Kalopanax septemlobus [89] have been documented.…”

Population demographic history of a temperate shrub, Rhododendron weyrichii (Ericaceae), on continental islands of Japan and South Korea

“…Statistical phylogeographic analyses of R. weyrichii populations using model‐based approaches revealed that history of population isolation between islands is likely to have a considerable influence on population survival on each island, even if the islands were sometimes connected geographically during climatic oscillations (Qi et al., 2014). Especially, differences in survival history due to the suitability of isolated habitats are reflected in the current effective population size on each island.…”

“…Validation of the distribution model was performed, using default settings with 100 replicates of cross‐validation procedures, with 25% of the data used for model testing, implemented in Maxent v. 3.3.3e (Phillips et al., 2006). Five bioclimatic variables (annual mean temperature, mean temperature in the driest quarter, annual precipitation, precipitation in the wettest quarter, and precipitation in the driest quarter), which showed high values of area under curve (AUC) and are critically important for temperate species that are distributed in humid and warm environments, were chosen for inclusion in the distribution model, as they have been used in ecological niche modeling for other species with similar distribution ranges (Qi, Yuan, Comes, Sakaguchi, & Qiu, 2014; Worth et al., 2013). …”

Molecular evidence reveals a closer relationship between Japanese and mainland subtropical specimens of a widespread tree species, Acer mono

“…Species mainly distributed in the subtropical region may also show different patterns compare to higher-latitudes species. Qi et al (2014) concluded that tall canopy trees with long generation times, abundant seeds and large effective population sizes tended to disperse across the ECS. However, understory plant species may be fragmented even when the land bridge is exposed (Table 1) because population recovery and colonization of those species in the forest interior may be negatively affected by those exterior species (Eriksson and Ehrl en, 1997;Suzuki et al, 2002).…”

“…There are also closely related species that are hypothesized to have dispersed across the KS, e.g., Picea jezoensis (Aizawa et al, 2007), Kalopanax septemlobus , and Neolitsea sericea (Lee et al, 2013). However, the ECS could also have blocked the gene flow of many species, such as Croomia japonica (Li et al, 2008), Kirengeshoma palmate (Qiu et al, 2009b), Ligularia hodgsonii (Wang et al, 2013), and Platycrater arguta (Qiu et al, 2009a;Qi et al, 2014). The KS could similarly have been a barrier and thereby responsible for allopatric speciation of Kirengeshoma palmata, a sister species of K. koreana (Qiu et al, 2009b).…”