Abstract
Subtropical China harbours the world’s most diverse temperate flora, but little is known about the roles of geographical and eco-climatic factors underlying the region’s exceptionally high levels of species diversity and endemism. Here we address this key question by investigating the spatio-temporal and ecological processes of divergence within the Dysosma versipellis-pleiantha species complex, endemic to subtropical China. Our cpDNA phylogeny showed that this monophyletic group of understory herbs is derived from a Late Pliocene ancestor of the Qinghai-Tibetan Plateau (QTP)/Southwest China. Genetic and ENM data in conjunction with niche differentiation analyses support that the early divergence of D. versipellis and D. pleiantha proceeded through allo-peripatric speciation, possibly triggered by Early Pleistocene climate change, while subsequent climate-induced cycles of range contractions/expansions enhanced the eco-geographical isolation of both taxa. Furthermore, modelling of population-genetic data indicated that major lineage divergences within D. versipellis likely resulted from long-term allopatric population isolation in multiple localized refugia over the last glacial/interglacial periods, and which in turn fostered endemic species formation (D. difformis, D. majoensis) from within D. versipellis in Southwest China. These findings point to an overriding role of Quaternary climate change in triggering essentially allopatric (incipient) speciation in this group of forest-restricted plant species in subtropical China.
Highlights
Across subtropical China (Fig. 1a,b)[16,18]
Cheng ex Ying and D. pleiantha (Hance) Woodson, form a parapatric species pair with abutting ranges in East China; the former occurs in isolated stands of montane warm-temperate deciduous (WTD) forest [c. 800–2000 (2700) m] throughout Central-East China, whereas D. pleiantha is associated with warm-temperate evergreen (WTE) forest habitats in the hilly/coastal areas of East China (300–800 m) and the mountains of Taiwan (1000–2500 m)
46 were specific to D. versipellis (H2–H46, H56), five to D. pleiantha (H47–H51) and three to D. difformis (H52–H54), while D. majoensis was fixed for H55 (Fig. 1a)
Summary
Across subtropical China (Fig. 1a,b)[16,18]. Two of them, D. versipellis (Hance) M. Cheng ex Ying and D. pleiantha (Hance) Woodson, form a parapatric species pair with abutting ranges in East China; the former occurs in isolated stands of montane WTD forest [c. Hiroe are rare endemics with proximate but non-overlapping ranges in the WTD forests of Central-Southwest China, where both are broadly sympatric (but usually not locally admixed) with D. versipellis (Fig. 1b). We combined phylogeographic analyses using both nuclear and cpDNA data with cpDNA-based phylogenetic and dating approaches at the genus level, as well as Approximate Bayesian Computation (ABC), (palaeo-)climatic data and niche identity tests, to elucidate the spatial-temporal and ecological processes of divergence within the species complex that eco-geographically varies across the two major forest biomes of subtropical China. The specific aims of this study were: (1) to evaluate the phylogenetic relationships and divergence times of the four focal species and their intraspecific lineages; (2) to compare patterns of genetic diversity and structure among these four species; and (3) to infer the phylogeographic and demographic history of the species complex, including levels of admixture and/or hybridization
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