Odor diversity decreases with inbreeding in the ant Hypoponera opacior

Reduction in heterozygosity can lead to inbreeding depression. This loss of genetic variability especially affects diverse loci, such as immune genes or those encoding recognition cues. In social insects, nestmates are recognized by their odor, i.e. their cuticular hydrocarbon profile. Genes underlying hydrocarbon production are thought to be under balancing selection. If so, inbreeding should result in a loss of chemical diversity. We show here that cuticular hydrocarbon diversity decreases with inbreeding. Studying an ant with a facultative inbreeding lifestyle we found inbred workers to exhibit both a lower number of hydrocarbons and less diverse, that is, less evenly-proportioned profiles. The association with inbreeding was strong for methyl-branched alkanes, which play a major role in nestmate recognition, and for n-alkanes, whereas unsaturated compounds were unaffected. Shifts in allocation strategies with inbreeding in our focal species indicate that these ants can detect their inbreeding level and use this information to adjust their reproductive strategy. Our study is the first to demonstrate that odor profiles can encode information on inbreeding, with broad implications not only for social insects, but for sexual selection and mate choice in general. Odor profiles may constitute an honest signal of inbreeding, a fitness-relevant trait in many species.

杂合性（heterozygosity）降低可引发近交衰退（inbreeding depression）。这种遗传变异的丧失尤其会影响多样性基因座（loci），例如免疫基因或编码识别信号（recognition cues）的基因。在社会性昆虫中，个体通过气味——即表皮碳氢化合物谱（cuticular hydrocarbon profile）——识别同巢伙伴。调控碳氢化合物合成的基因被认为处于平衡选择（balancing selection）作用之下。若果真如此，近交应会导致化学多样性的丧失。本研究证实，表皮碳氢化合物多样性随近交程度升高而降低。我们以一种具有兼性近交生活史（facultative inbreeding lifestyle）的蚂蚁为研究对象，发现近交工蚁的碳氢化合物数量更少，且谱图多样性更低，即组分比例更不均匀。该关联在甲基支链烷烃（methyl-branched alkanes，这类物质在同巢识别中发挥关键作用）以及正构烷烃（n-alkanes）中表现显著，而不饱和化合物（unsaturated compounds）则不受影响。本研究物种中，近交引发的资源分配策略变化表明，这些蚂蚁能够检测自身的近交水平，并利用该信息调整繁殖策略。本研究首次证实，气味谱图可以编码近交相关信息，其影响不仅局限于社会性昆虫，更对一般性的性选择（sexual selection）与配偶选择（mate choice）具有广泛意义。气味谱图或可作为近交的诚实信号（honest signal），而近交是诸多物种中与适合度（fitness）相关的重要性状。