Population genetics under the Massenerhebung effect: the influence of topography on the demography of Acer morrisonense (Sapindaceae)

Aim: The Massenerhebung effect (Mass elevation effect) refers to heat or wind-driven altitudinal distribution patterns of temperature-dependent parameters among massifs with narrower range and lower elevation around peripheral and isolated mountains compared to core and continuous ones. Although common in ecology, this effect is rarely discussed in population genetics. Here, we use genetic markers to reveal population genetic patterns and also test the mountain- and sky-barrier hypotheses relevant to the Massenerhebung distribution pattern of Acer morrisonense in Taiwan's rugged topography and varied local climates. Location: The alpine and cloud forest of Taiwan. Taxon: Acer morrisonense Hayata Methods: Two chloroplast DNA (cpDNA) fragments and 17 expressed sequence tag-simple sequence repeat (EST-SSR) loci respectively from 200 and 286 individuals were used to elucidate the phylogeographic pattern of pollen and seed dispersal of A. morrisonense. These data were combined with ecological niche modeling (ENM) to infer distribution range shifts and refugia. We also correlated the genetic-divergence indices with spatial factors to clarify latitudinal and altitudinal effects on genetic diversity. Results: The incongruent phylogeographic patterns of genetic distributions between nuclear and cpDNA markers indicate unhindered pollen flow but spatially constrained seed dispersal. Taken together with ENM, the genetic pattern further reflects historical colonization from central-mountain refugia to edges since the Holocene. The Massenerhebung reduces the gene flow by the surrounding mountains and also causes lower genetic diversity compared to central alpine populations. Main conclusions: This study is the first to reveal the influence of Massenerhebung effect on cpDNA genetic structure of montane trees and reflect the spatial trends of seed dispersal. This population genetic pattern can also be attributed to the demography-related range shifts with paleoclimate fluctuations under complex mountain topography, supporting the mountain-barrier hypothesis. The results have important implications for conserving the genetic diversity of species with a wide altitudinal distribution range.

研究目的：山岳隆起效应（Massenerhebung effect，即Mass elevation effect）指相较于核心连续山地，周边孤立山体的海拔范围更窄、海拔更低，其温度依赖参数的海拔分布格局受热或风驱动调控。该效应虽在生态学领域广为报道，但在种群遗传学研究中却鲜有涉及。本研究以台湾地形崎岖、气候多样的区域为研究背景，利用遗传标记揭示玉山槭（Acer morrisonense）的种群遗传格局，并检验与其山岳隆起效应分布格局相关的山地屏障与天空屏障假说。
研究区域：中国台湾的高山与云雾林生境。
研究类群：玉山槭（Acer morrisonense Hayata）。
研究方法：分别对200个个体扩增得到两段叶绿体DNA（cpDNA）片段，对286个个体扩增得到17个表达序列标签-简单序列重复（EST-SSR）位点，以此解析玉山槭的花粉与种子扩散的系统地理格局。结合生态位模型（ENM）推断物种分布范围变迁与避难所分布；同时将遗传分化指数与空间因子进行关联分析，以阐明纬度与海拔对遗传多样性的影响效应。
研究结果：核基因标记与cpDNA标记所揭示的遗传分布系统地理格局存在显著不一致，表明花粉扩散不受空间限制，但种子扩散存在空间约束。结合生态位模型结果，该遗传格局进一步反映出全新世以来，物种从中部山地避难所向周边边缘区域的历史拓殖过程。山岳隆起效应通过周边山地限制了种群间的基因交流，且相较于中部高山种群，边缘种群的遗传多样性更低。
主要结论：本研究首次揭示了山岳隆起效应对山地树木叶绿体DNA遗传结构的影响，并反映出种子扩散的空间分布趋势。该种群遗传格局同时可归因于复杂山地地形下，伴随古气候波动的种群历史动态与分布范围变迁，支持山地屏障假说。本研究结果对于海拔分布跨度较大的物种的遗传多样性保护具有重要的理论与实践指导意义。