Data from: Growing up with feces: benefits of allo-coprophagy in families of the European earwig

An important issue in the evolution of group living is the risk of pathogen and predator exposure entailed by the inherent accumulation of feces within a nesting site. While many group living species limit this risk by cleaning the nest, others do not, raising questions about the benefits of maintaining feces in the nest and their importance in social evolution. Here, we investigated whether one of these benefits could be mediated by coprophagy in families of the European earwig, Forficula auricularia. In this insect species, mothers and mobile juveniles (nymphs) line their nests with feces and consume them. In a first experiment, we tested whether access to feces produced by either nymphs or mothers affects nymph survival in both presence and absence of food. The results showed that access to sibling feces, but not mother feces, enhanced offspring survival under food deprivation. Such an effect did not occur when regular food was available. We then conducted a food-choice experiment to reveal whether nymphs prefer food to feces, and if they discriminate between feces from their mother, unrelated adult females, unrelated nymphs, or their siblings. We found that offspring generally preferred regular food to feces, but nevertheless always consumed some feces. By contrast, nymphs showed no preference between related sibling or mother feces and did not discriminate between feces from related and unrelated individuals. Overall, our results suggest that the benefits of coprophagy could favor the maintenance of feces within the nest and promote the evolution of social life.

群居演化中的一个重要议题，是筑巢位点内粪便固有堆积所带来的病原体与捕食者暴露风险。尽管诸多群居物种会通过清理巢穴来降低此类风险，但另有部分物种并未采取该策略，这引发了关于保留巢内粪便的益处及其在社会演化中的重要性的诸多疑问。本研究以欧洲蠼螋（Forficula auricularia）的类群为对象，探究其中一项潜在益处是否可通过食粪行为（coprophagy）介导。在该昆虫类群中，母虫与活动期若虫会将粪便铺于巢穴内并取食粪便。在首个实验中，我们测试了若虫接触若虫产生的粪便或母虫产生的粪便，会如何影响若虫在有食物与无食物条件下的存活率。结果显示，在食物匮乏条件下，接触同胞粪便可提升后代存活率，而接触母虫粪便则无此效果；当有常规食物供应时，该效应并未出现。随后我们开展了食物选择实验，以探究若虫是否更偏好食物而非粪便，以及它们能否区分母虫粪便、无关成年雌虫粪便、无关若虫粪便与同胞粪便。我们发现，后代总体上更偏好常规食物而非粪便，但仍会取食一定量的粪便。相较而言，若虫并未表现出对同胞粪便与母虫粪便的偏好，也无法区分亲缘个体与非亲缘个体的粪便。综上，我们的研究结果表明，食粪行为所带来的益处，或可推动巢内粪便的保留，并促进群居生活的演化。