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, <i>Mytilus galloprovincialis,</i> 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 <i>M. galloprovincialis</i>, although it is also possible that genetic variation for thermal sensitivity may allow for adaptation to changing environmental conditions.

海洋是人为气候变化引发的额外热量的巨大储汇，要精准预测物种对气候变化的响应，明确海洋生物各生命阶段的耐热性至关重要。对于营体外排放繁殖的海洋无脊椎动物而言，繁殖过程极为脆弱——精子与卵子会被直接释放至开阔水域中。随后配子将暴露于波动的环境条件下，这可能会影响其受精能力。本研究以地中海贻贝（Mytilus galloprovincialis）为模式物种，开展多组因子交配杂交实验，以评估个体在环境温度与升温条件下的受精率差异。整体而言，我们发现升温会使受精率出现小幅但显著的下降。不过，不同个体的响应存在显著的可塑性：部分个体在升温条件下受精率有所提升，但绝大多数个体的受精率均出现下降。本研究结果表明，海洋变暖可能会对地中海贻贝（M. galloprovincialis）未来的繁殖造成潜在代价，但与此同时，耐热敏感性的遗传变异或能为其适应不断变化的环境条件提供可能。