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，物种分布边缘的遗传变异水平应有所降低，但相关实证证据的支持力度尚不明确。本研究采用测序分型技术（genotyping-by-sequencing），对海洋腹足类履螺属（Crepidula）两个物种的中心种群与边缘种群的遗传变异情况展开探究。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可能存在差异。两个物种的中心种群的等位基因丰富度与私有等位基因占比均为最高，而边缘种群的这两项指标均更低。低扩散能力物种C. convexa在其整个分布范围内均表现出高度的遗传结构，这一结果与此前利用其他分子标记开展的研究所得出的格局相符。尽管此前研究发现高扩散能力物种C. fornicata在其大部分分布范围内几乎不存在遗传结构，但其最北端的种群仍与中部种群存在显著差异。尽管分布边缘的遗传多样性水平显著更低，但通过全基因组标记检测到的多样性绝对降幅较小，目前尚不清楚这些边缘种群是否会因此产生功能层面的影响。