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.

群居生活演化中的一项关键科学问题，是筑巢位点内粪便固有堆积所伴随的病原体暴露与捕食者侵扰风险。诸多群居物种会通过清洁巢穴来降低此类风险，但另有类群并未演化出此类行为，这引发了关于巢内保留粪便的益处及其在社会演化中的重要性的诸多研究问题。本研究以欧洲蠼螋（Forficula auricularia）的家族类群为研究对象，探讨食粪行为（coprophagy）是否可介导这类益处。在该昆虫物种中，母虫与活动性若虫（nymphs）会以粪便修饰巢穴并取食粪便。在首个实验中，我们分别在有食物与无食物的条件下，测试了接触若虫或母虫产生的粪便是否会影响若虫存活率。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应；当有常规食物可供取食时，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，以及它们能否区分亲代母虫、无关成年雌虫、无关若虫与同胞所产生的粪便。研究发现，子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，若虫对同胞粪便与母虫粪便并无偏好，也无法区分亲缘个体与非亲缘个体产生的粪便。综合来看，本研究结果表明，食粪行为所带来的益处，可能会推动巢内粪便的保留，并促进群居生活的演化。