Data from: Genetic differentiation but no reduction in genetic diversity at the northern range edge of two species with different dispersal modes

Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping-by-sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types, and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, C. convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high-dispersing species, C. fornicata, are distinct from more central populations, though this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genome-wide markers was slight, and it is not yet known if there are functional consequences for these marginal populations.

理论预测，物种分布范围边缘的遗传变异水平应有所降低，但相关实证支持尚无定论。本研究采用测序分型技术（genotyping-by-sequencing），对海洋腹足类履螺属（Crepidula）两个物种的核心种群与边缘种群的遗传变异情况展开调查。这两个物种具有不同的发育模式与扩散类型，因此其遗传变异的空间分布格局或存在差异。结果显示，两个物种的核心种群的等位基因丰富度与私有等位基因占比均为最高，边缘种群的这两项指标则相对更低。扩散能力较弱的加利福尼亚履螺（C. convexa）在其整个分布范围内均表现出高度的遗传结构，这与此前利用其他分子标记得到的研究结果相符。扩散能力较强的舟形履螺（C. fornicata）的最北部种群与核心种群存在显著分化，尽管此前研究发现该物种在其大部分分布范围内的遗传结构较弱。尽管分布范围边缘的遗传多样性水平显著降低，但利用全基因组分子标记检测到的多样性绝对降幅较小，目前尚不清楚这种降低会对边缘种群产生何种功能性影响。