Abstract:

Past climatic oscillations and complex geodynamic processes had tremendous effects on the current distributions of species in East Asia. Previous studies have revealed that spermatophytes experienced different demographic histories and survived in multiple refuges. However, very few studies involving ferns have been conducted over a large geographical area like East Asia. The monophyletic epiphytic fern genus Lemmaphyllum, which is composed of four species, is widespread in East Asia and offers a good model for exploring how geoclimatic oscillations influence the diversification and demographic history of fern species. We studied the phylogeography of Lemmaphyllum based on 115 populations using plastid sequences and ecological niche modeling. A total of 91 haplotypes were found in Lemmaphyllum. Molecular clock estimation revealed that speciation coincided with the three phases of the Qingzang Movement at beginning of the third uplift of Qinghai-Tibetan Plateau. The “Tanaka-Kaiyong Line” demarcated lineages within L. carnosum. The split of the mainland and island lineages of L. rostratum and L. carnosum var. microphyllum may have resulted from ancestral isolation whereby land-bridges acted as a “barrier” rather than as a “corridor” between mainland and island lineages. Multiple glacial refuges such as Sichuan Basin, Jinggangshan region, YGG region, HDM region, and the islands of the China East Sea during the LGM were revealed. The entities of Lemmaphyllum experienced species-specific demographic histories in response to the Pleistocene climate change. The case study of epiphytic ferns may provide evidences for understanding the migration of evergreen broad-leaf forest under climate oscillation.

Key words: genetic structure, glacial refuge, phylogeny, Polypodiaceae, Quaternary climatic oscillations, speciation