Genetic evidence and species distribution modelling reveal the response of Larix sibirica and its related species to Quaternary climatic and ancient historical events

Abstract

Larix Mill., a boreal forest genus, distributes in Eurasia and North America. Larix sibirica and some related species of this genus have wide distributions in the northeastern, northwestern and southwestern regions of China. To elucidate the response of populations to different regional historical events, we investigated the spatial genetic structures and the divergence time of genotypes in these Larix species based on two cpDNA fragments. To approach this question, we have also modelled the change of glacial-interglacial distributions for populations in different regions using the species distribution modelling. The results of analyses of molecular variance indicate genetic variation mainly occurred between three isolated regions (74.4%). Distributions of Larix have possibly undergone contractions during the Last Glacial Maximum (LGM) period in comparison with their present-day distributions in all three regions. Recent rapid uplift of Qinghai-Tibet Plateau likely promoted the high level of genetic diversity (π = 0.69 × 10−3, Hd = 0.711) and Plio-Pleistocene (1.9–2.7 Ma) lineage divergence in the southwestern region. Founder effect and genetic drift accompanied by postglacial colonizations are expected to shape one dominated haplotype and southern LGM distribution in the northeastern region. Quaternary Glacial period is also speculated to trigger low level of genetic diversity (π = 0.09 × 10−3, Hd = 0.133) in the northwestern region. Disjunction of L. sibirica and lineage divergence at about 1.6 Ma in the Altai Mountains and the eastern Tianshan Mountains are related to the enhanced aridity in the Asian interior and the desert expansion in Dzungarian Basin during the early Pleistocene.