Ocean acidification alters sperm responses to egg-derived chemicals in a broadcast spawning mussel

The continued and unprecedented emissions of anthropogenic carbon dioxide (CO2) are causing progressive ocean acidification (OA). While deleterious effects of OA on biological systems are well documented in the growth of calcifying organisms, lesser studied impacts of OA include potential effects on gamete interactions that determine fertilisation, which are likely to influence the many marine species that spawn gametes externally. Here, we explore the effects of OA on the signalling mechanisms that enable sperm to track egg-derived chemicals (sperm chemotaxis). We focus on the mussel Mytilus galloprovincialis, where sperm chemotaxis enables eggs to selectively bias fertilisation in favour of genetically compatible males. Using a factorial experimental design, we test whether the experimental manipulation of seawater pH (comparing ambient conditions to predicted end-of-century scenarios) alters these patterns of differential sperm chemotaxis. While we find no evidence that patterns of m...