Data from: Moderate genetic drift is driven by extreme recruitment events in the invasive mollusk Crepidula fornicata

Effective population size (Ne) is a measure of genetic drift and is thus a central parameter in evolution, conservation genetics and invasion biology. Interestingly, in native marine species, Ne is typically several orders of magnitude lower than the census size. This pattern has often been explained by high fecundity, variation in reproductive success and pronounced early mortality, resulting in genetic drift across generations. Data documenting genetic drift and/or Ne in marine invasive species are, however, still scarce. We examined the importance of genetic drift in the invasive species Crepidula fornicata by genotyping 681 juveniles sampled during each annual recruitment peak over nine consecutive years in the Bay of Morlaix (Brittany, France). Observed variations in genetic diversity were partially explained by variation in recruitment intensity. In addition, substantial temporal genetic differentiation was documented (that is, genetic drift), and was attributed to nonrandom variance in the reproductive success of different breeding groups across years in the study species. Using a set of single-sample and temporal estimators for Ne, we estimated Ne to be three or four orders of magnitude smaller than the census size (Nc). On one hand, this reduction in Ne relative to Nc appeared congruent with, although slight higher than, values commonly observed in native marine species. Particular life-history traits of this invasive species may play an important role in buffering genetic drift. On the other hand, Ne still remained far below Nc, hence, possibly reducing the efficiency of selection effects.

有效种群大小（Effective population size, Ne）是衡量遗传漂变的指标，因此是进化生物学、保护遗传学以及入侵生物学中的核心参数。有趣的是，在本土海洋物种中，Ne通常比普查种群大小低数个数量级。这一现象通常可通过高繁殖力、繁殖成功率的差异以及显著的早期死亡来解释，由此引发跨世代的遗传漂变。然而，有关海洋入侵物种遗传漂变和/或有效种群大小的记录数据仍然十分匮乏。我们通过对法国布列塔尼地区莫尔莱湾连续9年在年度补充高峰期采集的681份幼体样本进行基因分型，探究了入侵物种舟形履螺（Crepidula fornicata）中遗传漂变的重要性。观测到的遗传多样性变异可部分通过补充强度的差异得到解释。此外，研究还记录到显著的时间遗传分化（即遗传漂变），并将其归因于研究物种不同繁殖群体在多年间繁殖成功率的非随机变异。我们采用一套有效种群大小的单样本和时间序列估计方法，估算得到Ne比普查种群大小（Nc）小3至4个数量级。一方面，尽管略高于本土海洋物种中常见的数值，但有效种群大小相对于普查种群大小的这一缩减趋势与本土海洋物种的情况大体一致。该入侵物种的特定生活史特征可能在缓冲遗传漂变方面发挥了重要作用。另一方面，有效种群大小仍然远低于普查种群大小，因此可能会降低选择效应的作用效率。