Data from: Quantitative genetic architecture at latitudinal range boundaries: reduced variation but higher trait independence

Species distribution limits are hypothesized to be caused by small population size and limited genetic variation in ecologically relevant traits, but earlier studies have not evaluated genetic variation in multivariate phenotypes. We asked whether populations at the latitudinal edges of the distribution have altered quantitative genetic architecture of ecologically relevant traits compared with midlatitude populations. We calculated measures of evolutionary potential in nine Arabidopsis lyrata populations spanning the latitudinal range of the species in eastern and midwestern North America. Environments at the latitudinal extremes have reduced water availability, and therefore plants were assessed under wet and dry treatments. We estimated genetic variance-covariance (G-) matrices for 10 traits related to size, development, and water balance. Populations at southern and northern distribution edges had reduced levels of genetic variation across traits, but their G-matrices were more spherical; G-matrix orientation was unrelated to latitude. As a consequence, the predicted short-term response to selection was at least as strong in edge populations as in central populations. These results are consistent with genetic drift eroding variation and reducing the effectiveness of correlational selection at distribution margins. We conclude that genetic variation of isolated traits poorly predicts the capacity to evolve in response to multivariate selection and that the response to selection may frequently be greater than expected at species distribution margins because of genetic drift.

学界普遍假设物种分布边界由种群规模过小以及生态相关性状的遗传变异受限所导致，但此前的研究尚未对多变量表型的遗传变异展开评估。本研究旨在探究：相较于中纬度种群，分布区纬度边界处的种群，其生态相关性状的数量遗传架构是否发生了改变。我们针对分布于北美东部及中西部、覆盖该物种完整纬度分布范围的9个 lyrata 鼠耳芥（Arabidopsis lyrata）种群，计算了进化潜力相关指标。纬度极端区域的环境水分有效性较低，因此我们在湿润和干旱两种处理条件下对植株进行了评估。我们针对10项与植株体型、发育进程及水分平衡相关的性状，估算了遗传方差-协方差（G）矩阵。分布区南北边界的种群，其各性状的遗传变异水平均有所降低，但其G矩阵更趋近于球形；G矩阵的取向与纬度并无关联。因此，边界种群所预测的短期选择响应强度，至少与中心种群相当。上述结果与遗传漂变侵蚀遗传变异、削弱分布边界处相关选择有效性的假说相符。我们由此得出结论：单一性状的遗传变异，无法准确预测多变量选择下的进化能力；而由于遗传漂变的作用，物种分布边界处的选择响应往往可能高于预期。