Low pH Means More\nFemale Offspring: A Multigenerational\nPlasticity in the Sex Ratio of Marine Bivalves

Global changes can profoundly affect the sex determination\nand\nreproductive output of marine organisms, disrupting the population\nstructure and ecosystems. High\nCO<sub>2</sub>driven low pH in the context of ocean acidification\n(OA) has been shown to severely affect various calcifiers, but less\nis known about the extent to which low pH influences sex determination\nand reproduction of marine organisms, particularly mollusks. This\nstudy is the first to report a biased sex ratio over multiple generations\ntoward females, driven by exposure to high CO<sub>2</sub>-induced\nlow pH environments, using the ecologically and economically important\nPortuguese oyster (Crassostrea angulata) as a model. This phenomenon, which we term pH-mediated sex determination\n(PSD), has no consequences for fecundity, gonadal development, or\nreproductive function in the offspring. Moreover, PSD persisted into\na second year of reproduction and was inherited across multiple generations.\nTranscriptomic analysis indicates PSD is associated with the activation\nof the Wnt signaling pathway in females and inhibition of spermiogenesis-related\nfunctions in males. This work expands our understanding of environmental\nsex determination and highlights the possible impact of global changes\non reproduction and population dynamics of mollusks and other marine\norganisms.