Data from: Sex change and effective population size: implications for population genetic studies in marine fish

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 towards 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, was 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 life histories.

繁殖成功率的巨大差异是自然种群有效种群大小（Ne）降低的首要诱因。对于顺序雌雄同体（性转换）鱼类而言，其种群性比通常呈现偏态，且偏向于初始性别，而个体在完成性转换后繁殖成功率会大幅提升。因此，在其余参数基本一致的前提下，理论上性转换鱼类种群的有效种群大小（Ne）应低于雌雄异体（性别分离）物种。本研究采集了南非东海岸两种生态习性相似的鱼类的遗传数据，以此估算有效种群大小（Ne）：其一为雌雄异体的‘桑特’真鲷（Cheimerius nufar），其二为雌性先熟（初始性别为雌性）的性转换鱼类‘斯林格’真鲷（Chrysoblephus puniceus）。在本次研究的区域内，两种物种均未检测到遗传结构，亦未发现遗传多样性存在显著差异。雌性先熟物种的当代有效种群大小（Ne）估算值显著更低，但这一模式在历史时间尺度上并不明显。综上，本研究结果显示，顺序雌雄同体特性对有效种群大小（Ne）的影响会随时间尺度的不同而产生差异；同时，基于不同遗传模式的遗传标记所推断的种群特征信号，在结合性转换生活史进行解读时也需谨慎。