Data from: Local topography shapes fine-scale spatial genetic structure in the Arkansas Valley evening primrose, Oenothera harringtonii (Onagraceae)

Identifying factors that shape the spatial distribution of genetic variation is crucial to understanding many population- and landscape-level processes. In this study, we explore fine-scale spatial genetic structure in Oenothera harringtonii (Onagraceae), an insect-pollinated, gravity-dispersed herb endemic to the grasslands of south-central and southeastern Colorado, USA. We genotyped 315 individuals with 11 microsatellite markers and utilized a combination of spatial autocorrelation analyses and landscape genetic models to relate life history traits and landscape features to dispersal processes. Spatial genetic structure was consistent with theoretical expectations of isolation by distance, but this pattern was weak (Sp = 0.00374). Anisotropic analyses indicated that spatial genetic structure was markedly directional, in this case consistent with increased dispersal along prominent slopes. Landscape genetic models subsequently confirmed that spatial genetic variation was significantly influenced by local topographic heterogeneity, specifically that geographic distance, elevation and aspect were important predictors of spatial genetic structure. Among these variables, geographic distance was ~68% more important than elevation in describing spatial genetic variation, and elevation was ~42% more important than aspect after removing the effect of geographic distance. From these results, we infer a mechanism of hydrochorous seed dispersal along major drainages aided by seasonal monsoon rains. Our findings suggest that landscape features may shape microevolutionary processes at much finer spatial scales than typically considered, and stress the importance of considering how particular dispersal vectors are influenced by their environmental context.

探明调控遗传变异空间分布的影响因子，对于解析诸多种群与景观尺度的生态过程具有关键意义。本研究以哈氏月见草（Oenothera harringtonii，柳叶菜科Onagraceae）为研究对象，解析其精细尺度空间遗传结构；该物种为昆虫传粉、重力扩散的草本植物，为美国科罗拉多州中南部与东南部草原生境的特有种。我们采用11个微卫星标记（microsatellite markers）对315个个体开展基因分型，并结合空间自相关分析（spatial autocorrelation analyses）与景观遗传模型（landscape genetic models），探究生活史性状、景观特征与扩散过程之间的关联。其空间遗传结构符合隔离距离（isolation by distance）的理论预期，但该模式强度较弱（Sp = 0.00374）。各向异性分析（Anisotropic analyses）结果显示，空间遗传结构呈现显著的方向性，具体表现为沿显著坡度的扩散能力增强，与该模式相符。后续景观遗传模型验证表明，空间遗传变异显著受局地地形异质性（topographic heterogeneity）的影响，其中地理距离、海拔与坡向均为空间遗传结构的重要预测因子。在所有变量中，地理距离对空间遗传变异的解释度较海拔高约68%；而在剔除地理距离的影响后，海拔的解释度较坡向高约42%。基于上述结果，我们推断存在一种依托季节性季风雨、沿主要水系开展水力传播（hydrochorous）的种子扩散机制。本研究结果表明，景观特征对微进化过程（microevolutionary processes）的塑造作用可发生在远较以往研究更为精细的空间尺度上，同时也强调了探究特定扩散媒介（dispersal vectors）如何受其环境背景影响的重要性。