Data from: Chemical composition of preen wax reflects MHC similarity in songbirds

In jawed vertebrates, genes of the major histocompatibility complex (MHC) play a key role in immunity by encoding cell-surface proteins that recognise and bind non-self antigens. High variability at MHC suggests that these loci may also function in social signalling such as mate choice and kin recognition. This requires that MHC genotype covaries with some perceptible phenotypic trait. In mammals and fish, MHC is signalled chemically through volatile and nonvolatile peptide odour cues, facilitating MHC-dependent mate choice and other behaviours. In birds, despite evidence for MHC-dependent mating, candidate mechanisms for MHC signalling remain largely unexplored. However, feather preen wax has recently been implicated as a potential source of odour cues. We examined whether the chemical composition of preen wax correlates with MHC class IIβ genotypes of wild song sparrows (Melospiza melodia). Pairwise chemical distance reflected amino acid distance at MHC for male-female dyads, although not for same-sex dyads. Chemical diversity did not reflect MHC diversity. We used gas chromatography-mass spectrometry (GC-MS) to characterize preen wax compounds, and identified four wax esters that best reflect MHC similarity. Provided songbirds can detect variation in preen wax composition, this cue may allow individuals to assess MHC similarity and compatibility of potential mates.

在有颌脊椎动物中，主要组织相容性复合体（major histocompatibility complex, MHC）基因通过编码识别并结合非己抗原的细胞表面蛋白，在免疫反应中发挥关键作用。MHC基因座的高度多态性提示，这些基因座可能还在配偶选择、亲缘识别等社会信号传递过程中发挥功能，而这一功能的实现依赖于MHC基因型与某些可感知的表型性状存在关联。在哺乳类与鱼类中，MHC信息可通过挥发性与非挥发性肽类气味线索进行化学传递，从而介导依赖MHC的配偶选择及其他行为。尽管已有证据表明鸟类存在依赖MHC的交配行为，但目前关于MHC信号传递的潜在机制仍未得到充分探索。不过近年来，理羽蜡被认为是气味线索的潜在来源之一。本研究针对野生歌带鹀（Melospiza melodia）的理羽蜡化学成分是否与其MHC II类β链基因型存在关联展开了调查。结果显示，雌雄配对组的两两化学距离可反映其MHC区域的氨基酸距离，但同性配对组则无此关联；理羽蜡的化学多样性与MHC多样性并无关联。本研究通过气相色谱-质谱联用（gas chromatography-mass spectrometry, GC-MS）对理羽蜡化合物进行了表征，并筛选出四种可最优反映MHC相似性的蜡酯。若鸣禽能够感知理羽蜡化学成分的差异，这一线索便可帮助个体评估潜在配偶的MHC相似性与适配性。