Investment in immunity is expected to decrease (costly immunity) or enhance (terminal investment) reproductive performance. Here, we tested the effects of activation of the immune system in female great tits (Parus major) on (1) their reproductive effort and (2) the survival and body condition of their offspring, controlling for chick sex. We injected females tending 3-day-old chicks with sheep red blood cells (SRBC) or saline (control) and recorded their provisioning rates 6 days later, during the expected peak of antibody production. We measured tarsus length and body mass in 11-day-old chicks and monitored changes in brood size. We found that female provisioning rates were unaffected by the SRBC challenge. An analysis without an outlier, however, showed a significant challenge-by-hatch date interaction. This interaction indicated that female provisioning rates decreased with hatch dates in the SRBC but not in the control nests, suggesting a stronger effect in later breeders. Chick body mass was not affected by female immunisation nor by its interaction with chick sex. However, we found a significant challenge-by-sex interaction on offspring tarsus. In SRBC nests, the difference in tarsus length between male and female chicks was lower than in controls, suggesting sex-dependent effects of the challenge on offspring structural growth. Finally, chick mortality was greater in SRBC nests compared with controls, but chick survival probability was not affected by sex. Overall, our results support the costly immunity but not the terminal investment hypothesis in the great tit.

免疫投资预计会减少（成本高昂的免疫力）或增强（终端投资）生殖性能。在这里，我们测试的女性大山雀的免疫系统激活的效果（大山雀）（1）繁殖力和（2）后代的生存和身体状况，控制雏鸡的性行为。我们向育有3天大的小鸡的雌性注射绵羊红细胞（SRBC）或生理盐水（对照），并在抗体产生预期的高峰期6天后记录它们的供应率。我们测量了11日龄小鸡的体长度和体重，并监测了育雏尺寸的变化。我们发现，女性配给率不受SRBC挑战的影响。但是，没有异常值的分析表明，每次孵化日期之间都有很大的挑战。这种相互作用表明，雌性供应率随着孵化日期的增加而降低，但在对照巢中却没有，这表明在后来的种鸡中效果更强。雏鸡的体重不受女性免疫力及其与雏鸡性别的相互作用的影响。但是，我们在后代上发现了重大的性别挑战。在SRBC巢中，雄性和雌性小鸡的sus体长度差异低于对照组，这表明挑战对后代结构生长的性别依赖性影响。最后，与对照组相比，SRBC巢中的雏鸡死亡率更高，但雏鸡的存活概率不受性别的影响。总体而言，我们的结果支持成本高昂的免疫力，但不支持最终投资假设。表明挑战对后代结构生长的性别依赖性影响。最后，与对照组相比，SRBC巢中的雏鸡死亡率更高，但雏鸡的存活概率不受性别的影响。总体而言，我们的结果支持成本高昂的免疫力，但不支持最终投资假设。表明挑战对子代结构生长的性别依赖性影响。最后，与对照组相比，SRBC巢中的雏鸡死亡率更高，但雏鸡的存活概率不受性别的影响。总体而言，我们的结果支持成本高昂的免疫力，但不支持最终投资假设。