Engelhardia roxburghiana, a wind-pollinated tropical and subtropical evergreen tree of the walnut family (Juglandaceae), exhibits a wide distribution from subtropical China to Indonesia. The distribution pattern of E. roxburghiana, along with the fossil records, provides a valuable framework for investigating the biogeographic history of this taxon in Hainan Island and the adjacent mainlands, as well as investigate the evolutionary trajectories of the lineage in these regions.
In a study published in Palaeogeography, Palaeoclimatology, Palaeoecology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators conducted large-scale sampling in Hainan Island and its neighboring continents and deeply explored its genetic diversity, genetic structure, divergence time, and population dynamic history based on restriction site-associated DNA sequencing (RAD-seq) data from E. roxburghiana. By combining climate model data, they assessed the suitable distribution areas of this species at different times, aiming to more accurately reveal the biogeographic pattern of this region.
A total of 242 individuals of E. roxburghiana were collected from 50 locations in Hainan Island and its neighboring landmasses.Their large-scale sampling and RAD-seq data of E. roxburghiana provided insights into the palaeogeography of Hainan Island and adjacent mainland areas.
Through genetic structure and divergence time analysis, it was found that E. roxburghiana dispersed from mainland China to Hainan Island via land bridge during the late Oligocene, and that Hainan Island was not connected with Vietnam and Guangxi at that time.
The distribution area of E. roxburghiana expanded northward with the retreat of an arid belt on mainland Asia, and higher precipitation during the Miocene and the modern East Asian Summer Monsoon (EASM) ultimately facilitated the diversification of E. roxburghiana. Moreover, the different trajectories of three groups in effective population size and species distribution modelling indicate a refugium in southern China during the Quaternary glaciations and in the future.
“Our study successfully reveals the evolutionary trajectory of Engelhardia roxburghiana, reconstructs the biogeographic patterns of Hainan Island and the mainland, and provides important clues for understanding its speciation and evolution process,” said MENG Honghu of XTBG.
Contact
MENG Honghu Ph.D
Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China
E-mail: menghonghu@xtbg.ac.cn
First published: 24 July 2024
