Sex change and the genetic structure of marine fish populations

The interaction between environmental forces and dispersal characteristics is largely responsible for the patterns of population structure in marine fish. Yet, crucial gaps in knowledge on life-histories and the relative contributions of numerous environmental factors still hinder a thorough understanding of marine population connectivity. One life-history trait so far overlooked by most fish population geneticists is sequential hermaphroditism, whereby individuals first mature as one sex and later in life reverse into the other sex. Population genetic theory predicts that sex-changing fish will present a higher potential for more spatially structured populations than gonochoristic species, as a result of their naturally skewed sex ratio, which is expected to reduce effective population size and hence increase genetic drift. We gathered published data on genetic population structure in marine fish, as summarized by the popular F-ST index, and - after controlling for several potentially confounding factors - we tested the hypothesis that sex-changing species are more genetically structured than gonochoristic ones. Although we found no evidence to support the theoretical expectations, our results suggest new working hypotheses that can stimulate new research avenues at the intersection between physiology, genetics and fisheries science.