Data from: Enhanced male coloration after immune challenge increases reproductive potential

In many animal species, females select a mate on the basis of the expression of secondary sexual traits. A prevalent theory suggests that male ornaments are reliable indicators of immunocompetence, because the cost of immune function prevents cheating. However, sexual signalling is a component of males’ reproductive effort, and an immune challenge may also alter the organism’s perceived future prospects and hence their signalling effort. In this study, to investigate the consequences of mounting an immune response on signalling effort, blue-footed booby males (Sula nebouxii) during courtship were inoculated with diphtheria–tetanus vaccine. We found that, after this immune challenge, on average males increased their signalling effort but lost more body mass compared to control males. Importantly, vaccination affected the partner’s reproductive decisions: compared to control females, females paired with vaccinated males laid eggs earlier, and increased clutch volume in early pairs. Overall, our results suggest that blue-footed booby males invest more in sexual signals when future breeding opportunities are at risk, eliciting a greater reproductive investment by their partners. Increased signaling effort by infected individuals may contrast the idea of sexual ornaments as signals of infection status.

在众多动物物种中，雌性通常会依据第二性征（secondary sexual traits）的表达来选择配偶。主流理论认为，雄性装饰性状是免疫能力（immunocompetence）的可靠指标，因为免疫功能的代价会阻断欺骗行为的发生。然而，性信号传递（sexual signalling）属于雄性繁殖投入的一部分，而免疫挑战（immune challenge）同样可能改变个体对未来繁殖前景的评估，进而影响其信号传递投入。本研究为探究启动免疫应答对信号传递投入的影响，对求偶期的雄性蓝脚鲣鸟（Sula nebouxii）接种了白喉-破伤风疫苗（diphtheria–tetanus vaccine）。我们发现，经此免疫挑战后，相较于对照组雄性，实验组雄性平均提升了其信号传递投入，但同时体重流失更多。尤为重要的是，疫苗接种影响了雌性配偶的繁殖决策：相较于对照组雌性，与接种疫苗雄性配对的雌性产卵时间更早，且在早期配对组中提升了窝卵量（clutch volume）。综合来看，我们的研究结果表明，当未来繁殖机会面临风险时，雄性蓝脚鲣鸟会加大性信号的投入，进而促使其配偶投入更多繁殖资源。个体在免疫挑战后提升信号传递投入的现象，与“雄性装饰性状可反映感染状态”这一经典观点相悖。