Abstract
Climatic oscillations in the Pleistocene have had profound effects on the demography and genetic diversity of many extant species. Cycas guizhouensis Lan & R.F. Zou is an endemic and endangered species in Southwest China that is primarily distributed along the valleys of the Nanpan River. In this study, we used four chloroplast DNAs (cpDNA), three nuclear genes (nDNA) and 13 microsatellite (SSR) loci to investigate the genetic structure, divergence time and demographic history of 11 populations of C. guizhouensis. High genetic diversity and high levels of genetic differentiation among the populations were observed. Two evolutionary units were revealed based on network and Structure analysis. The divergence time estimations suggested that haplotypes of C. guizhouensis were diverged during the Middle-Upper Pleistocene. Additionally, the demographic histories deduced from different DNA sequences were discordant, but overall indicated that C. guizhouensis had experienced a recent population expansion during the post-glacial period. Microsatellite data revealed that there was a contraction in effective population size in the past. These genetic features allow conservation measures to be taken to ensure the protection of this endangered species from extinction.
Highlights
Different regions have experienced different scales and frequencies of glaciations in the Pleistocene[1]
The four chloroplast DNAs (cpDNA) regions surveyed across the 110 individuals (11 populations, Table S1) of C. guizhouensis identified 12 haplotypes in total
Detection of recombination in nuclear genes showed that no recombination occurred in GTP and PHYP
Summary
Different regions have experienced different scales and frequencies of glaciations in the Pleistocene[1]. Cycads are generally considered to be the oldest group of living seed plants Cycads reached their greatest levels of diversity during the Jurassic-Cretaceous (approximately 199.6 to 65.5 million years ago, MYA). In South China, Cycas species generally grow on low-altitude slopes of ridges and cliffs along river valleys Their fertile seeds are large, heavy and sink in water, which precludes water dispersal over long distances. In plant species, both the mating system and dispersal mechanism have important effects on genetic differentiation among populations[24,25]. C. guizhouensis has been severely threatened by rapid habitat destruction for the cultivation of economic plants and over-collection because of its edible stem and ornamental attributes This species has dramatically decreased in numbers and is becoming endangered. The need to develop effective protection measures for this species is urgent
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