Population dynamics linked to glacial cycles in Cercis chuniana F.P. Metcalf (Fabaceae) endemic to the montane regions of southern China

Abstract

The mountains of southern China are an excellent system for investigating the processes driving the geographic distribution of biodiversity and radiation of plant populations in response to Pleistocene climate fluctuations. How the key mountain ranges in southern China have affected the evolution of narrowly distributed species is less studied than more widespread species. Here we focused on Cercis chuniana, a woody species endemic to the southern mountain ranges in subtropical China, to elucidate its population dynamics. We used genotyping by sequencing (GBS) to investigate the spatial pattern of genetic variation among 11 populations. Bayesian time estimation revealed that population divergence occurred in the middle Pleistocene, when populations in the Nanling Mts. separated from those to the east. Geographical isolation was detected between the populations located in adjacent mountain ranges, thought to function as geographical barriers due to their complex physiography. As inferred by ecological niche modeling and coalescent simulations, secondary contact occurred during the warm Lushan-Tali interglacial period in China, with intensified East Asia summer monsoon and continuous habitat available for occupation. Complex physiography plus long-term stable ecological conditions across glacial cycles facilitated the demographic expansion in the Nanling Mts., from which contemporary migration began. Our work shows that population genomic approaches are effective in detecting the population dynamics of narrowly distributed species. This study advances our understanding how glacial cycles have affected the evolutionary history of plant species in southern China montane ecosystems.