Data from: Testing the influence of family structure and outbreeding depression on heterozygosity-fitness correlations in small populations

Theory predicts that positive Heterozygosity-Fitness Correlations (HFC) arise as a consequence of inbreeding, which is often assumed to have a strong impact in small, fragmented populations. Yet according to empirical data, HFC in such populations seem highly variable and impredictible. We here discuss two overlooked phenomena that may contribute to this variation. First, in a small population, each generation may consist of a few families. This generates random correlations between particular alleles and fitness (AFC, Allele-Fitness Correlations) and results in too liberal tests for HFC. Second, in some contexts, small populations receiving immigrants may be more impacted by outbreeding depression than by inbreeding depression, resulting in negative rather than positive HFC. We investigated these processes through a case study in tadpole cohorts of Pelodytes punctatus living in small ponds. We provide evidence for a strong family structure and significant AFC in this system, as well as an example of negative HFC. By simulations, we show that this negative HFC cannot be a spurious effect of family structure, and therefore reflects outbreeding depression in the studied population. Our example suggests that a detailed examination of AFC and HFC patterns can provide valuable insights into the internal genetic structure and sources of fitness variation in small populations.理论预测，正的杂合度-适合度相关性（Heterozygosity-Fitness Correlations, HFC）是近交的结果，而近交通常被认为对小型、破碎化种群具有强烈影响。然而现有实证数据显示，此类种群中的HFC表现出极高的变异性且难以预测。本文探讨了两种可能加剧该变异的未被充分关注的现象。其一，在小型种群中，每一代可能仅由少数家系构成。这会导致特定等位基因与适合度之间产生随机相关性，即等位基因-适合度相关性（Allele-Fitness Correlations, AFC），并使得HFC检验过于宽松。其二，在某些情境下，接纳外来个体的小型种群受到远交衰退的影响可能甚于近交衰退，进而产生负向而非正向的HFC。我们以栖息于小型池塘的斑背蟾（Pelodytes punctatus）蝌蚪群为案例研究对象，对上述过程进行了探究。本研究证实该系统中存在显著的家系结构与等位基因-适合度相关性，并提供了一例负向HFC的实例。通过模拟实验，我们证明该负向HFC并非家系结构带来的虚假效应，而是反映了研究种群中的远交衰退。本案例表明，对AFC与HFC模式展开细致分析，可为小型种群的内部遗传结构以及适合度变异来源提供极具价值的研究视角。