The influence of environmental conditions on sex determination in the blue mussel Mytilus edulis

The factors affecting sex determination remain largely unknown for most bivalve species. Environmental factors, such as temperature, are known to influence sex determination in some species, and this has been hypothesized for the mussel Mytilus edulis, but not experimentally validated yet. Adult exposure to different environmental conditions during gametogenesis, which occurs seasonally, may also affect offspring phenotype, including sex determination. Intergenerational carryover effects have been reported in bivalves, but the impact of parental exposures on offspring sex determination has not been examined so far. To address these questions, artificial fertilizations were performed on individuals collected in three different years and their embryos were reared at three different temperatures to specifically test if the environment influences offspring sex ratio through effects on parental developing gametes and/or on developing embryos. The analysis of 1938 embryos from 25 crosses revealed a significant effect of both temperature treatments and sampling years on the proportion of females. However, the overall variation is mostly explained by the "temperature treatment x sampling years" interaction. Taken together, our results suggested that interannual environmental variations experienced by the parents (during gametogenesis) and embryo (during development) can influence the sex of the offspring in M. edulis.