Geographic factors and climatic fluctuation drive the genetic structure and demographic history of Cycas taiwaniana (Cycadaceae), an endemic endangered species to Hainan Island in China

Genetic Differentiation and Relationship among Castanopsis chinensis, C. qiongbeiensis, and C. glabrifolia (Fagaceae) as Revealed by Nuclear SSR Markers

Castanopsis chinensis (Spreng.) Hance is widespread in the subtropical forests of China. Castanopsis qiongbeiensis G.A. Fu and Castanopsis glabrifolia J. Q. Li & Li Chen are limited to the coastal beaches of Wenchang county in the northeast of Hainan Island, and have similar morphological characteristics to C. chinensis. It is supposed that C. qiongbeiensis and C. glabrifolia are closely related to C. chinensis. In the present study, the genetic differentiation, gene flow, and genetic relationship of C. chinensis, C. qiongbeiensis, and C. glabrifolia were investigated by using 15 nuclear microsatellite markers; a total of 308 individuals from 17 populations were sampled in the three species. The allelic variation of nuclear microsatellites revealed moderate but significant genetic differentiation (FCT = 0.076) among C. chinensis, C. qiongbeiensis, and C. glabrifolia, and genetic differentiation between C. chinensis and C. glabrifolia was larger than that between C. chinensis and C. qiongbeiensis. Demographic simulations revealed unidirectional gene flow from C. chinensis to C. glabrifolia and C. qiongbeiensis, which highlight dispersal from mainland to island. The isolation effect of Qiongzhou Strait increased the genetic differentiation of species on both sides of the strait; however, the differentiation was diminished by gene flow that occurred during the historical period when Hainan Island was connected to mainland China. Our results supported the argument that C. glabrifolia should be considered an independent species and argued that C. qiongbeiensis should be regarded as an incipient species and independent conservation unit.

Geographic factors and climatic fluctuation drive the genetic structure and demographic history of Cycas taiwaniana (Cycadaceae), an endemic endangered species to Hainan Island in China

Hainan Island had experienced several cold-warm and dry-humid fluctuations since the Late Pleistocene period, resulting in separating and connecting from the mainland several times with the cyclic rise and fall of sea level. The fluctuations can change the biota and ecological environment in the island. Cycas taiwaniana Carruthers is endemic to Hainan Island and is classified as endangered by the International Union for Conservation of Nature (IUCN). To comprehensively understand the genetic dynamics of C. taiwaniana, we sampled 12 wild populations in Hainan Island and one cultivated population in Fujian province, and analyzed the genetic diversity, genetic structure, and demographic history based on the molecular data. Results revealed that C. taiwaniana had relatively low genetic diversity and high genetic differentiation. Haplotypes of C. taiwaniana diversified during the Pleistocene based on the chloroplast DNA (cpDNA) and the concatenated nuclear DNA (nDNA) data. Genetic cluster analyses based on the microsatellite (SSR) data showed that the 12 wild populations were separated into three clusters which could be three evolutionary significant units (ESUs), indicating three basic units of protection were identified. Moreover, we also confirmed the cultivated population FJ derived from the DLS1-GSL clade. Demographic inference from different data was discordant, but overall, it uncovered that C. taiwaniana had experienced population contraction events twice during the Pleistocene and Holocene, and then expanded recently. Our study elucidated the population genetic characteristics of C. taiwaniana, and guided us to develop targeted conservation and management strategies for this endangered species.