Back to the brink: phylogeography and demographic history of the endangered Torreya jackii

Both natural and anthropogenic factors can negatively affect species demography and even lead to species extinction, but their relative importance in driving species rarity remains poorly understood. To this end, we investigated the phylogeography and demographic history of the endemic endangered conifer species Torreya jackii. We collected samples from all the 13 extant wild populations, and analyzed the genetic variation using 8 nuclear microsatellites and 4 chloroplast and 1 mitochondrial DNA fragments. Low genetic and nucleotide diversity was revealed, which could explain the absence of spatial and phylogeographic structure. Using a hierarchical approximate Bayesian computation technique, we identified the demographic scenario that best fit with the genetic data, where the effective population size of the plant was low at least 200,000 years ago but expanded after the last glacial maximum (LGM). The scenarios accounting for population decline during the LGM had significantly smaller...自然与人为干扰因子均可对物种种群动态产生负面影响，甚至引发物种灭绝，然而二者在推动物种稀有性形成过程中的相对重要性仍未得到充分阐释。为此，我们针对特有濒危针叶树种长叶榧树（Torreya jackii）的系统地理学（phylogeography）与种群历史展开了研究。我们采集了该物种全部13个现存野生种群的样本，并借助8个核微卫星（nuclear microsatellites）标记、4个叶绿体DNA（chloroplast DNA）片段及1个线粒体DNA（mitochondrial DNA）片段对其遗传变异进行了分析。研究揭示该物种具有较低的遗传多样性与核苷酸多样性，这或可解释其缺乏空间结构与系统地理结构的现象。我们采用分层近似贝叶斯计算（hierarchical approximate Bayesian computation）技术，筛选出最适配遗传数据的种群历史情景：该物种的有效种群大小（effective population size）至少在20万年前便处于较低水平，但在末次冰盛期（last glacial maximum, LGM）之后发生了扩张。而考虑末次冰盛期种群衰退的情景，其拟合度显著更低……