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.

群居演化中的一项关键议题是：巢穴内粪便固有堆积所带来的病原体与捕食者暴露风险。诸多群居物种会通过清洁巢穴来降低此类风险，但仍有部分物种并未采取这类行为，这引发了关于巢穴留存粪便的益处及其在社会演化中的重要性的相关疑问。本研究以欧洲蠼螋（Forficula auricularia）类群为研究对象，探讨食粪行为（coprophagy）是否介导了其中一项益处。在该昆虫物种中，母虫与活动期幼体（若虫，nymph）会在巢穴中铺设粪便并食用粪便。我们首先开展了一项实验，检验接触若虫或母虫所产的粪便，是否会在有食物与无食物的条件下对若虫存活率产生影响。结果显示，在食物匮乏条件下，接触同胞粪便可提升子代存活率，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常规食物而非粪便，以及是否会区分来自母虫、无关成年雌虫、无关若虫或同胞所产的粪便。我们发现，子代总体上更偏好常规食物而非粪便，但仍会食用部分粪便。与之相反，若虫并未表现出对同胞粪便与母虫粪便的偏好差异，也无法区分亲缘个体与非亲缘个体所产的粪便。综合来看，本研究结果表明，食粪行为所带来的益处，或可促进巢穴内粪便的留存，并推动社会性生活的演化。