Dispersal abilities play a crucial role in shaping the extent of population genetic structure, with more mobile species being panmictic over large geographical ranges and less mobile ones organized in metapopulations exchanging migrants to different degrees. In turn, population structure directly influences the coalescence pattern of the sampled lineages, but the consequences on the estimated variation of the effective population size (N_e) over time obtained by means of unstructured demographic models remain poorly understood. However, this knowledge is crucial for biologically interpreting the observed N_e trajectory and further devising conservation strategies in endangered species. Here we investigated the demographic history of four shark species (Carharhinus melanopterus, Carharhinus limbatus, Carharhinus amblyrhynchos, Galeocerdo cuvier) with different degrees of endangered status and life history traits related to dispersal distributed in the Indo-Pacific and sampled off New Caledonia. We compared several evolutionary scenarios representing both structured (metapopulation) and unstructured models and then inferred the N_e variation through time. By performing extensive coalescent simulations, we provided a general framework relating the underlying population structure and the observed N_e dynamics. On this basis, we concluded that the recent decline observed in three out of the four considered species when assuming unstructured demographic models can be explained by the presence of population structure. Furthermore, we also demonstrated the limits of the inferences based on the sole site frequency spectrum and warn that statistics based on linkage disequilibrium will be needed to exclude recent demographic events affecting meta-populations.

中文翻译：

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融合时间、生活史特征和保护问题：以印太地区四种沿海鲨鱼物种为例

分散能力在塑造种群遗传结构的程度方面起着至关重要的作用，更多的移动物种在大的地理范围内泛滥，而在不同程度上交换移民的元种群中组织的流动性更小的物种。反过来，种群结构直接影响采样谱系的合并模式，但对通过非结构化人口模型获得的有效种群大小 ( N _e ) 随时间的估计变化的影响仍然知之甚少。然而，这一知识对于从生物学上解释观察到的N _{e至关重要。}轨迹并进一步制定濒危物种的保护策略。在这里，我们调查了四种鲨鱼物种（Carharhinus melanopterus、Carharhinuslimbatus、Carharhinus amblyrhynchos、Galeocerdo cuvier）的人口历史，它们具有不同程度的濒危状态和与分布在印度-太平洋地区和新喀里多尼亚的散布相关的生活史特征。我们比较了代表结构化（元种群）和非结构化模型的几个进化场景，然后推断出N _e随着时间的变化。通过进行广泛的聚结模拟，我们提供了一个与潜在种群结构和观察到的N _e动力学相关的通用框架。在此基础上，我们得出结论，当假设非结构化人口模型时，最近观察到的四个被考虑物种中有三个的下降可以用种群结构的存在来解释。此外，我们还证明了基于单一站点频谱的推断的局限性，并警告说，需要基于连锁不平衡的统计数据来排除最近影响元种群的人口统计事件。