Multilocus Analyses Reveal Postglacial Demographic Shrinkage of Juniperus morrisonicola (Cupressaceae), a Dominant Alpine Species in Taiwan

Postglacial climate changes alter geographical distributions and diversity of species. Such ongoing changes often force species to migrate along the latitude/altitude. Altitudinal gradients represent assemblage of environmental, especially climatic, variable factors that influence the plant distributions. Global warming that triggered upward migrations has therefore impacted the alpine plants on an island. In this study, we examined the genetic structure of Juniperus morrisonicola, a dominant alpine species in Taiwan, and inferred historical, demographic dynamics based on multilocus analyses. Lower levels of genetic diversity in north indicated that populations at higher latitudes were vulnerable to climate change, possibly related to historical alpine glaciers. Neither organellar DNA nor nuclear genes displayed geographical subdivisions, indicating that populations were likely interconnected before migrating upward to isolated mountain peaks, providing low possibilities of seed/pollen dispersal across mountain ranges. Bayesian skyline plots suggested steady population growth of J. morrisonicola followed by recent demographic contraction. In contrast, most lower-elevation plants experienced recent demographic expansion as a result of global warming. The endemic alpine conifer may have experienced dramatic climate changes over the alternation of glacial and interglacial periods, as indicated by a trend showing decreasing genetic diversity with the altitudinal gradient, plus a fact of upward migration.

冰期后气候变化会改变物种的地理分布与物种多样性。此类持续发生的气候变化往往迫使物种沿纬度或海拔梯度迁移。海拔梯度蕴含一系列影响植物分布的环境变量，尤以气候因子为重。因此，由全球变暖引发的向上迁移，已对台湾地区的高山植物造成影响。本研究以台湾地区优势高山物种台湾圆柏（Juniperus morrisonicola）为研究对象，解析其遗传结构，并基于多位点分析推断其历史种群动态。北部种群的遗传多样性水平较低，表明高纬度种群易受气候变化影响，这可能与历史高山冰川活动有关。无论是细胞器DNA还是核基因，均未呈现地理分化特征，这暗示在种群向上迁移至孤立山峰之前，各群体间存在广泛的基因交流，跨山脉的种子/花粉传播可能性较低。贝叶斯天际线图分析结果显示，台湾圆柏种群曾经历稳定增长，随后出现近期的种群收缩。与之相反，多数低海拔植物因全球变暖而出现近期的种群扩张。该特有高山针叶类植物可能在冰期-间冰期交替过程中经历了剧烈的气候变化，这一结论可由两点佐证：其一，遗传多样性随海拔梯度升高呈下降趋势；其二，该物种存在向上迁移的现象。