Many species are structured in social groups (SGs) where individuals exhibit complex mating strategies. Yet, most population genetic studies ignore SGs either treating them as small random-mating units or focusing on a higher hierarchical level (the population). Empirical studies acknowledging SGs have found an overall excess of heterozygotes within SGs and usually invoke inbreeding avoidance strategies to explain this finding. However, there is a lack of null models against which ecological theories can be tested and inbreeding avoidance quantified. Here, we investigate inbreeding (deviation from random mating) in an endangered forest-dwelling pair-living lemur species (Propithecus tattersalli). In particular, we measure the inbreeding coefficient (FIS) in empirical data at different scales: SGs, sampling sites and forest patches. We observe high excess of heterozygotes within SGs. The magnitude of this excess is highly dependent on the sampling scheme: while offspring are characterised by a high excess of heterozygotes (FIS < 0), the reproductive pair does not show dramatic departures from Hardy–Weinberg expectations. Moreover, the heterozygosity excess disappears at larger geographic scales (sites and forests). We use a modelling framework that incorporates details of the sifaka mating system but does not include active inbreeding avoidance mechanisms. The simulated data show that, although apparent “random mating” or even inbreeding may occur at the “population” level, outbreeding is maintained within SGs. Altogether our results suggest that social structure leads to high levels of outbreeding without the need for active inbreeding avoidance mechanisms. Thus, demonstrating and measuring the existence of active inbreeding avoidance mechanisms may be more difficult than usually assumed.

中文翻译：

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金冠狐猴社会结构的遗传后果

许多物种在个体表现出复杂的交配策略的社会群体 (SG) 中构成。然而，大多数群体遗传学研究忽略了 SG，要么将它们视为小的随机交配单位，要么专注于更高等级的层次（群体）。承认 SG 的实证研究发现 SG 内杂合子总体过量，并且通常会调用近交避免策略来解释这一发现。然而，缺乏可以测试生态理论和量化近亲繁殖避免的无效模型。在这里，我们研究了一种濒临灭绝的森林栖息的成对生活狐猴物种（Propithecus tattersalli）的近亲繁殖（偏离随机交配）。特别是，我们在不同尺度的经验数据中测量近交系数 (FIS)：SG、采样点和森林斑块。我们观察到 SG 内杂合子的数量过多。这种过剩的程度很大程度上取决于抽样方案：虽然后代的特征是杂合子高度过剩（FIS < 0），但生殖对并未显示出与 Hardy-Weinberg 预期的显着偏离。此外，杂合性过剩在更大的地理尺度（地点和森林）中消失。我们使用的建模框架包含了 sifaka 交配系统的详细信息，但不包括主动近交避免机制。模拟数据表明，虽然明显的“随机交配”甚至近亲繁殖可能发生在“种群”水平，但在 SGs 内仍保持近亲繁殖。总之，我们的研究结果表明，社会结构导致高水平的近亲繁殖，而不需要积极的近亲繁殖避免机制。因此，