Evolutionary history of the subnival flora of the Himalaya‐Hengduan Mountains: first insights from comparative phylogeography of four perennial herbs

Abstract

Aim The Himalaya-Hengduan Mountain (HHM) biodiversity hotspot including the 'sky islands' of Southwest China harbour exceptional plant diversity and endemicity at subnival summits (most of them exceeding 4300 m a.s.l.). This study is the first using a comparative phylogeographical framework to gain insights into the temporal origin of this highly fragmented subnival flora, and the historical factors shaping its genetic architecture as exemplified by four perennial herbs.Location Himalaya-Hengduan Mountains, China.Methods Based on nuclear and/or chloroplast (cp) DNA sequences for each of the four studied species, we performed AMOVA and mismatch distributional analyses to assess molecular structure, diversity and demographic history in relation to current and last glacial distributions using ecological niche modelling (ENM). Time-calibrated phylogenetic reconstructions of cpDNA data were used to infer species-specific stem and crown ages. ResultsOur time estimates suggest that these species originated during the Late Pliocene or early-to-mid Pleistocene, whereas their onset of diversification generally falls into the mid-Pleistocene. All four species exhibited island-like population genetic structures, with all of them showing signatures of recent population growth and/or spatial expansion based on cpDNA. By contrast, ENM indicated that species broad-scale distributions remained fairly stable over the last glacial/post-glacial cycle. Main conclusionsThe temporal origin of the four subnival HHM species is likely associated with tectonic changes in the region, while their near-simultaneous onset of diversification during the 'Naynayxungla Glaciation' (0.72-0.50 Ma) could reflect initial population divergence through climate-induced habitat fragmentation. Despite a rather stable distributional history, geographical population isolation and localized range expansion/contractions likely resulted in significant genetic structure and differentiation over the last glacial/ post-glacial cycle. Overall, the present results are strongly indicative of shared evolutionary histories and phylogeographical structures among subnival plants from the 'sky island system' of the HHM region.

Genetic Structure and Evolutionary History of Three Alpine Sclerophyllous Oaks in East Himalaya-Hengduan Mountains and Adjacent Regions

“…When combined with the general lack of IBD, The island-like population genetic structure of three oak species in accordance with their highly fragmented habitats located in the EH-HM region, and largely driven by historical effects of genetic drift rather than currently limited gene flow alone (Hutchison and Templeton, 1999). In fact, similar genetic structure have also been detected in other species in this region, such as Garrulax elliotii from the eastern Himalayas (Qu et al, 2011) and four herbs from HHM region (Luo et al, 2015). …”

Warm–cold colonization: response of oaks to uplift of the Himalaya–Hengduan Mountains

“…Moreover, the high level of total genetic diversity and low levels of within‐population diversity are typical for high mountainous plants, especially in island‐like populations (Luo et al . ). Previous studies have shown that species restricted to sky islands commonly have high levels of interpopulation genetic divergence (Shepard & Burbrink ), consistent with the significant differentiation between these oak populations.…”

The borage family (Boraginaceae s.str.): A revised infrafamilial classification based on new phylogenetic evidence, with emphasis on the placement of some enigmatic genera

“…On the other hand, Chionocharis hookeri (C.B.Clarke) I.M.Johnst. is a highly distinctive species of high alpine cushion-forming plants (3500-5800 m) distributed from northeast India to China (Zhu & al., 1995;Luo & al., 2016). Johnston (1924) suggested a close relationship with the Himalayan Lasiocaryum I.M.Johnst.…”