Data from: Birdsong signals individual diversity at the major histocompatibility complex

The major histocompatibility complex (MHC) plays a key role in vertebrate immunity, and pathogen-mediated selection often favours certain allelic combinations. Assessing potential mates' MHC profiles may provide receivers with genetic benefits (identifying MHC-compatible mates and producing optimally diverse offspring) and/or material benefits (identifying optimally diverse mates capable of high parental investment). Oscine songbirds learn songs during early life, such that song repertoire content can reflect population of origin while song complexity can reflect early life condition. Thus birdsong may advertise the singer's genetic dissimilarity to others in the population (and, presumably, compatibility with potential mates), or individual genetic diversity (and thus condition-dependent material benefits). We tested whether song repertoire content and/or complexity signal MHC class IIβ dissimilarity and/or diversity in male song sparrows (Melospiza melodia). Pairwise dissimilarity in repertoire content did not predict MHC dissimilarity between males, suggesting that locally rare songs do not signal rare MHC profiles. Thus, geographical variation in song may not facilitate MHC-mediated inbreeding or outbreeding. Larger repertoires were associated with intermediate MHC diversity, suggesting intermediate rather than maximal MHC diversity is optimal. This could reflect trade-offs between resisting infection and autoimmune disorders. Song complexity may advertise optimal MHC diversity, a trait affecting disease resistance and capacity for parental care.主要组织相容性复合体（major histocompatibility complex, MHC）在脊椎动物免疫中发挥关键作用，而病原体介导的选择往往会青睐特定的等位基因组合。评估潜在配偶的MHC特征，可为择偶者带来两类益处：其一为遗传益处，即识别与自身MHC兼容的配偶，繁育出遗传多样性最优的后代；其二为实际繁育益处，即识别出具备高亲代抚育能力、遗传多样性最优的配偶。鸣禽（oscine songbirds）会在生命早期习得鸣唱，因此鸣唱曲目内容可反映其起源种群，而鸣唱复杂度则可反映其早期生存状况。如此一来，鸣唱或可传递鸣唱者与种群中其他个体的遗传差异（据推测可反映其与潜在配偶的兼容性），或是个体的遗传多样性，进而传递依赖于个体状态的繁育收益。我们以雄性歌带鹀（Melospiza melodia）为研究对象，检验其鸣唱曲目内容和/或复杂度是否能够作为MHC II类β链（MHC class IIβ）差异程度与/或多样性的信号。分析结果显示，个体间鸣唱曲目内容的两两差异，无法预测雄性个体之间的MHC差异，这表明当地稀有鸣唱并不传递稀有MHC特征。因此，鸣唱的地理变异或许无法促进MHC介导的近交或远交。鸣唱曲目规模更大的个体，其MHC多样性处于中间水平，这提示最优的MHC多样性为中间型而非最大化型。这一现象或可反映抵御感染与自身免疫病之间的进化权衡。鸣唱复杂度或可传递最优MHC多样性的信号，而该性状同时影响个体的抗病能力与亲代抚育能力。