Plasticity of fertilization rates under varying temperature in the broadcast spawning mussel, Mytilus galloprovincialis

Oceans are a huge sink for the increased heat associated with anthropogenic climate
change, and it is vital to understand the heat tolerance of marine organisms at all
life stages to accurately predict species’ responses. In broadcast spawning marine
invertebrates, reproduction is a vulnerable process in which sperm and eggs are released
directly into the open water. Gametes are then exposed to fluctuating environmental
conditions that may impact their fertilizing capacity. Using the broadcast spawning
Mediterranean mussel, Mytilus galloprovincialis, as a model species, we performed blocks of factorial mating crosses to assess the
variance in fertilization rates among individuals under both ambient and elevated
temperatures. Overall, we found a small, but significant decline in fertilization
rates with elevated temperatures. However, there was substantial plasticity in responses,
with particular mussels having increased fertilization under elevated temperatures,
although the majority showed decreased fertilization rates. Our results suggest possible
future reproductive costs to ocean warming in M. galloprovincialis, although it is also possible that genetic variation for thermal sensitivity may
allow for adaptation to changing environmental conditions.