Which contributes more to the relict flora distribution pattern in East Asia, geographical processes or climate change? New evidence from the phylogeography of Rehderodendron kwangtungense

Abstract

Abstract Background Relict species are important for enhancing the understanding of modern biogeographic distribution patterns. Although both geological and climatic changes since the Cenozoic have affected the relict flora in East Asia, the contributions of geographical processes remain unclear. Here, we studied the population differentiation history of the relict species Rehderodendron kwangtungense Hu during the Cenozoic. In this study, 138 individuals from 16 populations of R. kwangtungense were subjected to double digest restriction-site associated DNA sequencing (ddRAD-seq) and shallow genome sequencing. Results We studied the population structure and historical biogeography of the relict species R. kwangtungense. The genetic diversity within the R. kwangtungense populations was extremely low. Mantel tests revealed an isolation-by-distance pattern, and the evidence of pollen and fruit morphology suggested that the distribution pattern of R. kwangtungense formed prior to the Miocene. Between 23 and 21 Ma, R. kwangtungense underwent a period of rapid differentiation that coincided with the rise of the Himalayas and the establishment of the East Asian monsoon. According to ecological niche modelling (ENM) and population demographic history, the suitable area and effective population size of R. kwangtungense decreased sharply during the glacial period and expanded after the last glacial maximum (LGM). Conclusion Our study shows that the distribution pattern of southern China mountain relict flora may have developed during the panplain stage between the middle Oligocene and the early Miocene. Then, the flora later fragmented under the force of orogenesis, including intermittent uplift during the Cenozoic Himalayan orogeny and the formation of abundant rainfall associated with the East Asian monsoon.