The historical demography and genetic variation of the endangered Cycas multipinnata (Cycadaceae) in the red river region, examined by chloroplast DNA sequences and microsatellite markers.

Yi-Qing Gong,Khang Sinh Nguyen,Hiep Tien Nguyen,Qing-Qing Zhan,Yue-Hua Wang,Xun Gong,Roberto Papa

doi:10.1371/journal.pone.0117719

Abstract

Cycas multipinnata C.J. Chen & S.Y. Yang is a cycad endemic to the Red River drainage region that occurs under evergreen forest on steep limestone slopes in Southwest China and northern Vietnam. It is listed as endangered due to habitat loss and over-collecting for the ornamental plant trade, and only several populations remain. In this study, we assess the genetic variation, population structure, and phylogeography of C. multipinnata populations to help develop strategies for the conservation of the species. 60 individuals from six populations were used for chloroplast DNA (cpDNA) sequencing and 100 individuals from five populations were genotyped using 17 nuclear microsatellites. High genetic differentiation among populations was detected, suggesting that pollen or seed dispersal was restricted within populations. Two main genetic clusters were observed in both the cpDNA and microsatellite loci, corresponding to Yunnan China and northern Vietnam. These clusters indicated low levels of gene flow between the regions since their divergence in the late Pleistocene, which was inferred from both Bayesian and coalescent analysis. In addition, the result of a Bayesian skyline plot based on cpDNA portrayed a long history of constant population size followed by a decline in the last 50,000 years of C. multipinnata that was perhaps affected by the Quaternary glaciations, a finding that was also supported by the Garza-Williamson index calculated from the microsatellite data. The genetic consequences produced by climatic oscillations and anthropogenic disturbances are considered key pressures on C. multipinnata. To establish a conservation management plan, each population of C. multipinnata should be recognized as a Management Unit (MU). In situ and ex situ actions, such as controlling overexploitation and creating a germplasm bank with high genetic diversity, should be urgently implemented to preserve this species.

Highlights

The Cycad is considered an old lineage because of its ancient morphological characters and fossil records which could date to the Early Permian [1] or possibly even the late Carboniferous period [2]
One recent fossil-calibrated molecular phylogenetic study based on multiple DNA sequence data proposed that extant Cycads originated no more than 12 million years ago; the Cycads underwent a recent synchronous global rediversification beginning in the late Miocene, followed by a slowdown towards the recent [10]
Our sampling will not affect the regular growth of C. multipinnata, and it was solely used for scientific research

Summary

Introduction

The Cycad is considered an old lineage because of its ancient morphological characters and fossil records which could date to the Early Permian [1] or possibly even the late Carboniferous period (approximately 300 million years ago) [2]. One recent fossil-calibrated molecular phylogenetic study based on multiple DNA sequence data proposed that extant Cycads originated no more than 12 million years ago; the Cycads underwent a recent synchronous global rediversification beginning in the late Miocene, followed by a slowdown towards the recent [10]. As the basal lineage of the living cycads supported by both phylogenetic studies and the recent obtained genome size of nuclear DNA [11,12,13,14], is the sole genus of Cycadaceae, and one distinguishing character of Cycas from other Cycads in morphology is its leaflets with an obvious midrib, lacking lateral veins.

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