Coscia, I, Chopelet, J, Waples, R, Mann, B and Mariani, S
'Sex change and effective population size : implications for population genetic studies in marine fish'
, Heredity, 117
, pp. 251-258.
Large variance in reproductive success is the primary factor that reduces effective population size (Ne) in
natural populations. In sequentially hermaphroditic (‘sex-changing’) fish, the sex ratio is typically skewed
and biased toward the ‘first’ sex, while reproductive success increases considerably after sex change.
Therefore, sex-changing fish populations are theoretically expected to have lower Ne than gonochorists
(separate sexes), assuming all other parameters are essentially equal. In this study, we estimate Ne from
genetic data collected from two ecologically similar species living along the eastern coast of South
Africa: one gonochoristic, the ‘santer’ sea bream Cheimerius nufar, and one protogynous (female-first)
sex-changer, the ‘slinger’ sea bream Chrysoblephus puniceus. For both species, no evidence of genetic
structuring, nor significant variation in genetic diversity, were found in the study area. Estimates of
contemporary Ne were significantly lower in the protogynous species, but the same pattern was not
apparent over historical timescales. Overall, our results show that sequential hermaphroditism may affect
Ne differently over varying time frames, and that demographic signatures inferred from genetic markers
with different inheritance modes also need to be interpreted cautiously, in relation to sex-changing life40
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