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，正杂合度-适合度相关性（Heterozygosity-Fitness Correlations, HFC）是近交的产物，而近交通常被认为对小型破碎化种群具有显著影响。然而现有实证数据表明，此类种群中的HFC呈现出高度的变异性与不可预测性。 本文探讨了两种可能导致该变异的、此前被忽视的现象。其一，在小型种群中，每一世代可能仅由少数家族构成。这会在特定等位基因与适合度之间产生随机相关性（等位基因-适合度相关性，Allele-Fitness Correlations, AFC），并导致HFC检验过于宽松。其二，在部分情境下，接纳外来个体的小型种群所受的远交衰退影响，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点斑狭口蛙（Pelodytes punctatus）蝌蚪群为研究对象开展案例分析，对上述过程进行了探究。本研究为该系统中显著的家族结构与显著的AFC提供了实证证据，同时也呈现了一例负向HFC。通过模拟实验，我们证实该负向HFC并非家族结构带来的虚假效应，而是反映了研究种群中的远交衰退。 我们的案例表明，对AFC与HFC模式进行细致剖析，可为小型种群的内部遗传结构与适合度变异来源提供极具价值的研究视角。