Female Rose Bitterling Prefer MHC-Dissimilar Males: Experimental Evidence

The role of genetic benefits in female mate choice remains a controversial aspect of sexual selection theory. In contrast to “good allele” models of sexual selection, “compatible allele” models of mate choice predict that females prefer mates with alleles complementary to their own rather than conferring additive effects. While correlative results suggest complementary genetic effects to be plausible, direct experimental evidence is scarce. A previous study on the Chinese rose bitterling (Rhodeus ocellatus) demonstrated a positive correlation between female mate choice, offspring growth and survival, and the functional dissimilarity between the Major Histocompatibility Complex (MHC) alleles of males and females. Here we directly tested whether females used cues associated with MHC genes to select genetically compatible males in an experimental framework. By sequentially pairing females with MHC similar and dissimilar males, based on a priori known MHC profiles, we showed that females discriminated between similar and dissimilar males and deposited significantly more eggs with MHC dissimilar males. Notably, the degree of dissimilarity was an important factor for female decision to mate, possibly indicating a potential threshold value of dissimilarity for decision making, or of an indirect effect of the MHC.

遗传收益在雌性配偶选择中的作用，仍是性选择理论中颇具争议的议题之一。与性选择的“优良等位基因”模型不同，配偶选择的“兼容等位基因”模型预测：雌性更偏好携带与自身等位基因互补的雄性作为配偶，而非具备加性效应的雄性。尽管相关研究结果提示互补遗传效应具有合理性，但直接实验证据仍较为匮乏。此前一项针对中华鳑鲏（Rhodeus ocellatus）的研究显示，雌性配偶选择、后代生长与存活率，与雌雄个体主要组织相容性复合体（Major Histocompatibility Complex, MHC）等位基因的功能差异呈正相关。本研究通过实验范式，直接检验了雌性是否借助与MHC基因相关的信号，来选择遗传兼容性匹配的雄性。基于预先已知的MHC分型，我们将雌性依次与MHC相似及相异的雄性配对，结果发现雌性能够区分相似与相异的雄性，并在MHC相异的雄性处产卵量显著更高。值得注意的是，相异程度是雌性作出交配决策的重要影响因素，这或许提示决策过程中存在相异程度的临界阈值，或是MHC发挥间接效应的相关线索。