Data from: Delineating the roles of males and females in sperm competition

Disentangling the relative roles of males, females and their interactive effects on competitive fertilization success remains a challenge in sperm competition. In this study, we apply a novel experimental framework to an ideally suited externally fertilizing model system in order to delineate these roles. We focus on the chinook salmon, Oncorhynchus tshawytscha, a species in which ovarian fluid (OF) has been implicated as a potential arbiter of cryptic female choice for genetically compatible mates. We evaluated this predicted sexually selected function of OF using a series of factorial competitive fertilization trials. Our design involved a series of 10 factorial crosses, each involving two ‘focal’ rival males whose sperm competed against those from a single ‘standardized’ (non-focal) rival for a genetically uniform set of eggs in the presence of OF from two focal females. This design enabled us to attribute variation in competitive fertilization success among focal males, females (OF) and their interacting effects, while controlling for variation attributable to differences in the sperm competitive ability of rival males, and male-by-female genotypic interactions. Using this experimental framework, we found that variation in sperm competitiveness could be attributed exclusively to differences in the sperm competitive ability of focal males, a conclusion supported by subsequent analyses revealing that variation in sperm swimming velocity predicts paternity success. Together, these findings provide evidence that variation in paternity success can be attributed to intrinsic differences in the sperm competitive ability of rival males, and reveal that sperm swimming velocity is a key target of sexual selection.

在精子竞争研究领域，厘清雄性、雌性及其交互效应对竞争性受精成功率的相对作用，始终是一项颇具难度的研究课题。本研究针对一种极为适配的体外受精模式生物体系，运用全新的实验框架来阐明这些作用机制。本研究聚焦于奇努克鲑（Oncorhynchus tshawytscha），已有研究表明该物种的卵巢液（ovarian fluid, OF）可能作为隐秘雌性选择的介导因子，帮助雌性筛选遗传相容性更佳的配偶。本研究通过一系列析因竞争性受精实验，对卵巢液的这一预测性性选择功能进行了验证。我们的实验设计包含10组析因杂交组合，每组均纳入2尾"焦点"雄性竞争者，其精子与单尾"标准化"（非焦点）雄性的精子，在2尾焦点雌性的卵巢液环境中，竞争一组遗传背景均一的卵群。该实验设计使得我们能够将竞争性受精成功率的变异归因于焦点雄性、雌性（卵巢液）及其交互效应的差异，同时控制了由竞争者雄性精子竞争能力差异以及雄性-雌性基因型互作所导致的变异。借助该实验框架，我们发现精子竞争力的变异仅可归因于焦点雄性的精子竞争能力差异，后续分析进一步证实了这一结论：精子游动速度的变异能够预测父权成功率。综上，本研究结果证实，父权成功率的变异可归因于竞争者雄性精子竞争能力的固有差异，同时揭示了精子游动速度是性选择的关键作用靶标。