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.Fertilization success, genetic relatedness and mitochondrial lineage estimates from competitive sperm chemotaxis experimentSheet 1 contains the results of multi-step sperm competition laboratory trials in the presence of egg chemoattractants in the mussel Mytilus galloprovincialis. Columns included are experimental block number, focal male (sperm donor) ID, focal female (egg chemoattractant donor) ID, replicate (two for each focal male-female cross), focal male fertilization success, focal male failures (eggs not fertilized), and total eggs counted. Sheet 2 contains similar data, but with the two replicate fertilization success measures for each focal male-female cross combined into a single measure. This sheet also contains estimates of nuclear genetic relatedness of male-female pairs, and a column specifying whether males and females belong to different (0) or the same (1) phylogenetic mitochondrial lineage.Lymbery_et_al_Evolution_Letters_data.xls