Data from: Immunosenescence and the ability to survive bacterial infection in the red flour beetle Tribolium castaneum

1. In most animals, ageing is associated with a decline in immune function (immune senescence). However, different components of the immune system seem to age differentially, and many studies do not measure the ultimate fitness consequences of immune function after infection. Previous work shows that immune function may be traded off with other fitness components such as reproduction. It is possible that age alters the nature of these trade-offs, particularly in conjunction with factors such as gender and mating that can also affect investment in immune function. 2. We tested the impact of age, sex and mating on post-infection survivorship in Tribolium castaneum flour beetles, as well as the components of baseline constitutive innate immunity and external (secreted) immune function in uninfected individuals. We also tested whether the reproductive ability of uninfected females is traded off with immune function (baseline innate and external immunity) and post-infection survivorship across age groups. 3. We found that age, sex and mating significantly affected immune components and infection outcome, although the magnitude and nature of the impact varied in each case. We found that older beetles were more susceptible to infection by the pathogen Bacillus thuringiensis even though major components of the constitutive innate immune defence (antibacterial and phenoloxidase activity) remained unchanged or improved with age. Thus, these aspects of innate immunity cannot explain the observed decline in post-infection survival of older beetles. We did not find trade-offs between the reproductive ability of uninfected females and their immune function. In contrast to innate immunity, external immunity showed an overall decline with age but was also affected by sex and mating. Finally, we show that bacterial infection alters external immunity via complex interactions between age, sex and mating status. 4. Our work uncovers novel interactions between age, sex and mating that can determine the evolution and outcome of immunosenescence by affecting the time course of relative investment in different immune and fitness components.

1. 在多数动物中，衰老与免疫功能衰退（免疫衰老，immune senescence）相关联。然而，免疫系统的不同组分的衰老进程存在差异，且诸多研究并未检测感染后免疫功能对个体最终适合度的影响。既往研究表明，免疫功能可能与繁殖等其他适合度相关组分存在进化权衡。衰老可能会改变这类权衡的本质，尤其是在与性别、交配等同样会影响免疫资源投入的因素共同作用时。
2. 我们以赤拟谷盗（Tribolium castaneum）为研究对象，检测了年龄、性别与交配状态对其感染后存活率的影响，同时还检测了未感染个体的基础组成型固有免疫组分与外部（分泌型）免疫功能。此外，我们还验证了未感染雌性个体的繁殖能力是否与免疫功能（基础固有免疫与外部免疫）以及不同年龄组的感染后存活率存在权衡关系。
3. 研究结果显示，年龄、性别与交配状态均会显著影响免疫组分与感染结局，但此类影响的强度与本质因具体情境而异。我们发现，尽管组成型固有免疫防御的主要组分（抗菌活性与酚氧化酶（phenoloxidase）活性）随年龄保持稳定甚至有所提升，但老龄赤拟谷盗对苏云金芽孢杆菌（Bacillus thuringiensis）感染的易感性更高。因此，这类固有免疫特征无法解释老龄甲虫感染后存活率下降的观测结果。我们未发现未感染雌性个体的繁殖能力与其免疫功能之间存在权衡关系。与固有免疫不同，外部免疫整体随年龄下降，同时也受性别与交配状态的影响。最后，我们证实细菌感染会通过年龄、性别与交配状态之间的复杂相互作用，改变外部免疫功能。
4. 本研究揭示了年龄、性别与交配状态之间的全新相互作用，这类作用可通过调控不同免疫与适合度组分的相对投入时序，决定免疫衰老的演化进程与结局。