Data from: Climate structures genetic variation across a species' elevation range: a test of range limits hypotheses

Gene flow may influence the formation of species range limits, yet little is known about the patterns of gene flow with respect to environmental gradients or proximity to range limits. With rapid environmental change it is especially important to understand patterns of gene flow to inform conservation efforts. Here we investigate the species range of the selfing, annual plant, Mimulus laciniatus, in the California Sierra Nevada. We assessed genetic variation, gene flow, and population abundance across the entire elevation-based climate range. Contrary to expectations, within-population plant density increased towards both climate limits. Mean genetic diversity of edge populations was equivalent to central populations, however all edge populations exhibited less genetic diversity than neighboring interior populations. Genetic differentiation was fairly consistent and moderate among all populations and no directional signals of contemporary gene flow were detected between central and peripheral elevations. Elevation-driven gene flow (isolation by environment), but not isolation by distance was found across the species range. These findings were the same towards high- and low-elevation range limits and were inconsistent with two common center-edge hypotheses invoked for the formation of species range limits: 1) decreasing habitat quality and population size; 2) swamping gene flow from large, central populations. This pattern demonstrates that climate, but not center-edge dynamics, is an important range-wide factor structuring M. laciniatus populations. To our knowledge this is the first empirical study to relate environmental patterns of gene flow to range limits hypotheses. Similar investigations across a wide variety of taxa and life histories are needed.基因流可影响物种分布范围边界的形成，但目前针对环境梯度或分布边界邻近区域的基因流模式仍知之甚少。在环境快速变化的当下，明晰基因流模式以指导保护工作尤为关键。本研究以分布于加利福尼亚州内华达山脉的自交型一年生植物——裂叶沟酸浆（Mimulus laciniatus）为研究对象，对其整个海拔梯度对应的气候分布范围展开调查。我们全面评估了种群的遗传变异、基因流及种群丰度。与预期相悖的是，种群内植株密度在两类气候边界处均呈上升趋势。边缘种群的平均遗传多样性与核心种群相当，但所有边缘种群的遗传多样性均低于邻近的内部种群。所有种群间的遗传分化程度中等且相对一致，未在海拔核心区与外围区之间检测到当代基因流的定向信号。整个物种分布范围内存在由海拔驱动的基因流（环境隔离，isolation by environment），而非地理距离隔离（isolation by distance）效应。该研究结果在高海拔和低海拔分布边界处均一致，且与两类常用于解释物种分布边界形成的经典中心-边缘假说相悖：其一，生境质量与种群规模随向边界靠近而下降；其二，大型核心种群的基因流会对边缘种群产生淹没效应。该结果表明，气候而非中心-边缘动态，是调控裂叶沟酸浆种群结构的关键全域因子。据我们所知，本研究是首个将基因流的环境模式与物种分布边界假说相关联的实证研究。未来亟需针对各类类群与生活史类型开展类似研究。