Data from: MHC variation is related to a sexually selected ornament, survival and parasite resistance in common yellowthroats

Hamilton and Zuk (1982) proposed that females choose mates based on ornaments whose expression is dependent on their genetically based resistance to parasites. The Major Histocompatibility Complex (MHC) plays an important role in pathogen recognition and is a good candidate for testing the relationships between immune genes and both ornament expression and parasite resistance. We tested the hypothesis that female common yellowthroats prefer to mate with more ornamented males, because it is a signal of their MHC-based resistance to parasites and likelihood of survival. In this species, females prefer males that have larger black facial masks as extra-pair mates. Using pyrosequencing, we found that mask size was positively related to the number of different MHC class II alleles, as predicted if greater variation at the MHC allows for the recognition of a greater variety of pathogens. Furthermore, males with more MHC class II alleles had greater apparent survival, and resistance to malaria infection was associated with the presence of a particular MHC class II allele. Thus, extra-pair mating may provide female warblers with immunity genes that are related to parasite resistance, survival and the expression of a male ornament, consistent with good genes models of sexual selection.

汉密尔顿与祖克（1982）提出，雌性个体基于装饰性状选择配偶，这类性状的表达依赖于个体基于遗传的寄生虫抗性。主要组织相容性复合体（Major Histocompatibility Complex, MHC）在病原体识别中发挥关键作用，是检验免疫基因与装饰性状表达、寄生虫抗性之间关联的理想候选研究对象。我们针对这一假说开展了检验：普通黄喉莺（common yellowthroat）的雌性更倾向于与装饰更发达的雄性交配，因为这类装饰是雄性基于MHC的寄生虫抗性与生存概率的信号。在该物种中，雌性更偏好拥有更大面积黑色面部面罩的雄性作为婚外配偶。通过焦磷酸测序（pyrosequencing）技术，我们发现面部面罩的大小与MHC II类等位基因的数量呈正相关，这契合“MHC位点变异越大，可识别的病原体种类越多”的预测。进一步研究显示，携带更多MHC II类等位基因的雄性表观存活率更高，且对疟疾感染的抗性与某一特定MHC II类等位基因的存在相关。因此，婚外配对或许能为雌性黄喉莺提供与寄生虫抗性、生存能力及雄性装饰性状表达相关的免疫基因，这与性选择的优质基因模型（good genes models of sexual selection）相符。