Data from: Egg chemoattractants moderate intraspecific sperm competition

Interactions among eggs and sperm are often assumed to generate intraspecific variation in reproductive fitness, but the specific gamete-level mechanisms underlying competitive fertilization success remain elusive in most species. Sperm chemotaxis–the attraction of sperm by egg-derived chemicals—is a ubiquitous form of gamete signaling, occurring throughout the animal and plant kingdoms. The chemical cues released by eggs are known to act at the interspecific level (e.g., facilitating species recognition), but recent studies have suggested that they could have roles at the intraspecific level by moderating sperm competition. Here, we exploit the experimental tractability of a broadcast spawning marine invertebrate to test this putative mechanism of gamete-level sexual selection. We use a fluorescently labeled mitochondrial dye in mussels to track the real-time success of sperm as they compete to fertilize eggs, and provide the first direct evidence in any species that competitive fertilization success is moderated by differential sperm chemotaxis. Furthermore, our data are consistent with the idea that egg chemoattractants selectively attract ejaculates from genetically compatible males, based on relationships inferred from both nuclear and mitochondrial genetic markers. These findings for a species that exhibits the ancestral reproductive strategy of broadcast spawning have important implications for the numerous species that also rely on egg chemoattractants to attract sperm, including humans, and have potentially important implications for our understanding of the evolutionary cascade of sexual selection.学界普遍认为，卵子与精子的相互作用可引发繁殖适合度的种内变异，但在绝大多数物种中，支撑竞争性受精成功的具体配子层面机制仍未明晰。精子趋化性（sperm chemotaxis）——即卵子分泌的化学物质对精子的吸引作用——是一种广泛存在的配子信号形式，遍布动物界与植物界。已知卵子释放的化学信号可在种间层面发挥功能（例如促进物种识别），但近期研究表明，这类信号亦可通过调控精子竞争在种内层面发挥作用。本研究依托体外广播式产卵（broadcast spawning）海洋无脊椎动物的实验可操作性，对这一推测的配子层面性选择（sexual selection）机制展开验证。我们在贻贝实验中使用荧光标记线粒体染料（fluorescently labeled mitochondrial dye），实时追踪精子竞争受精过程中的成功率，并在任一物种中首次获得直接证据，证实竞争性受精成功可通过差异化的精子趋化性进行调控。此外，基于核与线粒体遗传标记推断的亲缘关系，我们的研究数据支持以下假说：卵子趋化因子可选择性吸引来自遗传相容雄性的精液。针对这一采用祖先繁殖策略——体外广播式产卵——的物种所取得的研究发现，对众多同样依赖卵子趋化因子吸引精子的物种（包括人类）具有重要的学术意义，同时也可能为我们理解性选择的进化级联效应提供关键启示。