Data from: Surrounding pathogens shape maternal egg care but not egg production in the European earwig

Pathogens are ubiquitous in nature and typically entail major fitness costs in their hosts. These costs can be particularly important when individuals exhibit poor immune defenses, as it is often the case during early developmental stages. Hence, selection should favor parental strategies limiting the risks of pathogen exposure and infection in their offspring. In this study, we investigated 1) whether females of the European earwig Forficula auricularia avoid areas contaminated with spores of the entomopathogenic fungus Metarhizium brunneum prior to and at egg laying, as well as 2) whether spore presence entails an increase in females’ investment into both pre-hatching forms of care and clutch quantity and quality. Our results first show that females did not avoid contaminated areas prior to and at egg laying. However, females returned to their eggs faster in presence of living spores compared to UV-killed or no spores. They were also more likely to construct a nest when in presence of both living and UV-killed spores (but only in one studied population). Finally, we found that spore presence did not influence maternal investment into egg grooming, egg gathering and egg defense, as well as into clutch quantity and quality. Overall, our results demonstrate that earwig females do not avoid contaminated environments, but could mitigate the associated costs of pathogen exposure by adjusting their level of egg care. These findings emphasize the importance of pathogens in the evolution of pre-hatching parental care and, more generally, in the emergence and maintenance of family life in nature.

病原体在自然界中广泛分布，且通常会对宿主造成显著的适合度成本。当个体免疫防御能力低下时（这在发育早期阶段常发生），这类成本的影响尤为突出。因此，自然选择应会青睐那些能降低子代接触病原体并受感染风险的亲本策略。
本研究旨在探究两个核心问题：1）欧洲球螋（Forficula auricularia）的雌虫是否会在产卵前及产卵期间，避开被昆虫病原真菌（entomopathogenic fungus）布氏绿僵菌（Metarhizium brunneum）孢子污染的区域；2）孢子的存在是否会提升雌虫对孵化前育幼行为的投入，以及产卵簇的数量与质量。
研究结果首先显示，雌虫并不会在产卵前及产卵期间避开被污染的区域。但相较于经紫外线灭活的孢子组或无孢子对照组，存活孢子存在时雌虫返回卵簇的速度更快。此外，当环境中同时存在存活孢子与紫外线灭活孢子时，雌虫更倾向于构筑巢穴（但该现象仅在一个研究种群中被观测到）。最后，我们发现孢子的存在并不会影响雌虫对卵梳理、卵簇聚集与卵防御行为的投入，也不会改变产卵簇的数量与质量。
总体而言，本研究结果表明，球螋雌虫并不会避开受病原体污染的环境，但可通过调整卵育幼行为的投入水平，减轻接触病原体所带来的相关成本。这些研究结果凸显了病原体在孵化前亲本育幼行为演化中的重要性，更广泛地说，也凸显了其在自然界中家族生活的起源与维持过程中的关键作用。