Data from: No evidence for MHC class II-based non-random mating at the gametic haplotype in Atlantic salmon

Genes of the major histocompatibility complex (MHC) are a likely target of mate choice due to their role in inbreeding avoidance and potential benefits for offspring immunocompetence. Evidence for female choice for complementary MHC alleles among competing males exists both for the pre- and the postmating stages. However, it remains unclear whether the latter may involve non-random fusion of gametes depending on gametic haplotypes resulting in transmission ratio distortion or non-random sequence divergence among fused gametes. We tested whether non-random gametic fusion of MHC-II haplotypes occurs in Atlantic salmon Salmo salar. We performed in vitro fertilizations that excluded inter-individual sperm competition using a split family design with large clutch sample sizes to test for a possible role of the gametic haplotype in mate choice. We sequenced two MHC-II loci in 50 embryos per clutch to assess allelic frequencies and sequence divergence. We found no evidence for transmission ratio distortion at two linked MHC-II loci, nor for non-random gamete fusion with respect to MHC-II alleles. Our findings suggest that the gametic MHC-II haplotypes play no role in gamete association in Atlantic salmon and that earlier findings of MHC-based mate choice most likely reflect choice among diploid genotypes. We discuss possible explanations for these findings and how they differ from findings in mammals.主要组织相容性复合体（major histocompatibility complex, MHC）基因因其在近交规避以及对后代免疫能力的潜在益处，极有可能成为配偶选择的靶标。现有证据显示，雌性在竞争雄性中选择互补MHC等位基因的现象，既存在于交配前阶段，也见于交配后阶段。然而，目前仍不清楚后者是否会依赖配子单倍型发生非随机配子融合，进而导致传递比率失真，或是融合配子间出现非随机的序列分化。我们针对大西洋鲑（Salmo salar）中是否存在MHC-II单倍型的非随机配子融合展开了实验验证。本研究采用拆分家系设计，使用大样本量的卵群开展体外受精实验，排除了个体间精子竞争的干扰，以检验配子单倍型在配偶选择中可能发挥的作用。我们对每个卵群的50枚胚胎的两个MHC-II基因座进行测序，以评估等位基因频率与序列分化情况。研究未发现两个连锁MHC-II基因座存在传递比率失真的证据，也未观察到与MHC-II等位基因相关的非随机配子融合现象。我们的结果表明，大西洋鲑的配子MHC-II单倍型并未在配子结合过程中发挥作用，而此前基于MHC的配偶选择研究结果，大概率反映的是二倍体基因型间的选择。我们讨论了本研究结果的可能解释，以及其与哺乳动物相关研究结果的差异。