Data from: Variation in the post-mating fitness landscape in fruitflies

Sperm competition is pervasive and fundamental to determining a male’s overall fitness. Sperm traits and seminal fluid proteins (Sfps) are key factors. However, studies of sperm competition may often exclude females that fail to remate during a defined period. Hence, the resulting datasets contain fewer data from the potentially fittest males that have most success in preventing female remating. It is also important to consider a male’s reproductive success before entering sperm competition, which is a major contributor to fitness. The exclusion of these data can both hinder our understanding of the complete fitness landscapes of competing males and lessen our ability to assess the contribution of different determinants of reproductive success to male fitness. We addressed this here, using the Drosophila melanogaster model system, by (i) capturing a comprehensive range of intermating intervals that define the fitness of interacting wild type males, and (ii) analysing outcomes of sperm competition using selection analyses. We conducted additional tests using males lacking the sex peptide (SP) ejaculate component versus genetically matched (SP+) controls. This allowed us to assess the comprehensive fitness effects of this important Sfp on sperm competition. The results showed a signature of positive, linear selection in wild type and SP+ control males on the length of the intermating interval and on male sperm competition defense. However, the fitness surface for males lacking SP was distinct, with local fitness peaks depending on contrasting combinations of remating intervals and offspring numbers. The results suggest that there are alternative routes to success in sperm competition and provide an explanation for the maintenance of variation in sperm competition traits.

精子竞争（sperm competition）普遍存在，是决定雄性整体适合度（fitness）的核心基础因素。精子性状与精浆蛋白（seminal fluid proteins, Sfps）均为关键影响因子。然而，现有精子竞争研究往往会排除在设定周期内未发生再次交配的雌性，由此得到的数据集会缺失潜在适合度最高的雄性的数据——这类雄性在阻止雌性再次交配方面表现最为出色。此外，在进入精子竞争阶段前的雄性繁殖成功情况同样是适合度的重要组成部分，却常被现有研究忽略。剔除此类数据，不仅会阻碍我们对竞争雄性完整适合度景观（fitness landscape）的认知，还会削弱我们评估繁殖成功的各类决定因子对雄性适合度贡献度的能力。本研究以黑腹果蝇（Drosophila melanogaster）为模式系统，针对这一问题展开了如下探究：（1）全面覆盖定义了野生型雄性交互适合度的各类交配间隔（intermating interval）区间；（2）通过选择分析（selection analyses）解析精子竞争的结局。此外，我们还分别使用缺失性肽（sex peptide, SP）射精组分的雄性与遗传匹配的SP+对照雄性开展了额外对照实验，以此评估这一重要精浆蛋白对精子竞争的全面适合度效应。研究结果显示，野生型与SP+对照雄性的交配间隔长度以及精子竞争防御能力（sperm competition defense）均受到正向线性选择作用。然而，缺失SP的雄性的适合度曲面则呈现出截然不同的特征，其局部适合度峰值取决于再次交配间隔与后代数量的对立组合。本研究结果表明，精子竞争的成功存在多条替代路径，并为精子竞争性状的变异维持机制提供了合理解释。