Data from: Age, pathogen exposure, but not maternal care shape offspring immunity in an insect with facultative family life

Background. To optimize their resistance against pathogen infection, individuals are expected to find the right balance between investing into the immune system and other life history traits. In vertebrates, several factors were shown to critically affect the direction of this balance, such as the developmental stage of an individual, its current risk of infection and/or its access to external help such as parental care. However, the independent and/or interactive effects of these factors on immunity remain poorly studied in insects. Results: Here, we manipulated maternal presence and pathogen exposure in families of the European earwig Forficula auricularia to measure whether and how the survival rate and investment into two key immune parameters changed during offspring development. The pathogen was the entomopathogenic fungus Metarizium brunneum and the immune parameters were hemocyte concentration and phenol/pro phenoloxidase enzyme activity (total-PO). Our results surprisingly showed that maternal presence had no effect on offspring immunity, but reduced offspring survival. Pathogen exposure also lowered the survival of offspring during their early development. The concentration of hemocytes and the total-PO activity increased during development, to be eventually higher in adult females compared to adult males. Finally, pathogen exposure overall increased the concentration of hemocytes - but not the total-PO activity - in adults, while it had no effect on these measures in offspring. Conclusions: Our results show that, independent of their infection risk and developmental stage, maternal presence does not shape immune defense in young earwigs. This reveals that pathogen pressure is not a universal evolutionary driver of the emergence and maintenance of post-hatching maternal care in insects.背景：为优化对病原体感染的抗性，生物个体需在免疫系统的资源投入与其他生活史性状之间寻求恰当平衡。在脊椎动物中，多项因素已被证实会显著影响这一平衡的取向，例如个体的发育阶段、当前感染风险，以及亲代抚育等外部帮助的获取途径。然而，上述因素对免疫的独立及交互效应，在昆虫类群中的相关研究仍较为匮乏。 结果：本研究以欧洲球螋（Forficula auricularia）的家族种群为实验对象，通过操控母方存在状态与病原体暴露情况，探究子代发育过程中存活率与两项关键免疫参数的投入变化。所用病原体为昆虫病原真菌（entomopathogenic fungus）布氏绿僵菌（Metarizium brunneum），待测免疫参数为血细胞（hemocyte）浓度与酚氧化酶/酚氧化酶原酶活性（总酚氧化酶活性，total-PO）。令人意外的是，研究结果显示母方存在对子代免疫无显著影响，但会降低子代存活率；病原体暴露同样会降低子代发育早期的存活率。血细胞浓度与总酚氧化酶活性随发育进程逐步升高，最终成年雌性的两项指标均显著高于成年雄性。最后，总体而言，病原体暴露会提升成年个体的血细胞浓度，但对总酚氧化酶活性无影响，而对子代的上述两项指标均无显著作用。 结论：本研究结果表明，无论子代的感染风险与发育阶段如何，母方存在均不会塑造幼年期球螋的免疫防御能力。这一发现揭示，病原体压力并非昆虫孵化后亲代抚育演化出现与维持的普适性进化驱动力。