Data from: Genetic compatibility underlies benefits of mate choice in an external fertilizer

Mate choice is a common feature of sexually-reproducing species. In sessile or sedentary external fertilizers however, direct interactions between reproductive partners are minimal, and instead mate recognition and choice must occur at the level of gametes. It is common for some sperm and egg combinations to have higher fertilization success than others, but it remains unclear whether differences in fertilization reflect gamete-level mate-choice (GMC) for paternal quality or parental compatibility. Here, we examine the mechanisms underlying GMC in an externally fertilizing ascidian. A manipulative mate-choice assay confirmed that offspring viability was greater in clutches where we allowed GMC than in clutches where we precluded GMC. Complementary, quantitative genetic experiments then revealed that paternal quality effects were generally weaker than parental compatibility effects, particularly for the trait combination underlying the benefits of GMC. Overall, our data suggest that gametes that are more compatible at fertilization produce more viable offspring than gametes that are less compatible at fertilization. Therefore, although the regalia we typically associate with sexual selection are absent in external fertilizers, mechanisms that allow females to bias fertilization in favour of some males over others produce significant fitness benefits in organisms reproducing via the ancestral strategy.配偶选择是有性生殖物种的普遍特征。然而，对于固着或营固生活的体外受精生物而言，生殖伴侣间的直接互动极为有限，因此配偶识别与选择需通过配子层面完成。部分精卵组合的受精成功率往往高于其他组合，但目前仍不清楚受精成功率的差异是否反映了针对父本质量或亲本相容性层面的配子水平配偶选择（gamete-level mate-choice (GMC)）。本研究以一种体外受精的海鞘为研究对象，探讨了配子水平配偶选择背后的作用机制。控制性配偶选择实验证实，允许配子水平配偶选择的卵群，其后代存活力显著高于阻断该机制的卵群。后续补充的数量遗传学实验则显示，父本质量效应整体弱于亲本相容性效应，尤其在与配子水平配偶选择益处相关的性状组合中更为明显。总体而言，本研究数据表明，受精过程中相容性更高的配子，其所产生的后代存活力优于相容性较低的配子。因此，尽管体外受精生物缺乏我们通常与性选择相关联的标志性特征，但允许雌性偏向某些雄性的受精偏好机制，仍能通过祖先式繁殖策略为生物带来显著的适合度收益。