Influence of the reproductive cycle and sex on microplastic toxicity in mussels

Plastic contamination has become a major scientific and societal concern. While research on this issue has been flourishing over the last decade, several aspects remain insufficiently explored, including the chemical impact of plastic leachates (i.e., a complex mix of chemical compounds released by plastic particles). Furthermore, essential biological factors, such as the reproductive cycle and sex, are still largely overlooked, particularly in marine invertebrates, further limiting our ability to fully assess the ecotoxicological risks posed by pollutants. Here, we investigate the influence of these biological factors on organismal sensitivity to microplastic leachates (MPL) using two mussel species, Mytilus edulis and Mytilus galloprovincialis, which are important ecosystem engineers with significant economic values. The role of reproductive cycle was assessed in M. edulis through aggregation assays, while sex-based differences in sensitivity were assessed in M. galloprovincialis through byssal thread production assays. M. edulis showed increased sensitivity to MPL post-spawning, through a delay in their time to form their first aggregation, while female M. galloprovincialis showed higher sensitivity to MPL through increased byssal thread production. The observed effects may result from the high energetic cost of reproduction, coupled with potential endocrine-disrupting effects of plastic additives, highlighting the need for further studies. Our work stresses the importance of incorporating biological factors, such as the reproductive cycle and sex, into pollution risk assessments to enhance their ecological relevance.