Data from: Feces production as a form of social immunity in an insect with facultative maternal care

Background: Social animals have the unique capability of mounting social defenses against pathogens. Over the last decades, social immunity has been extensively studied in species with obligatory and permanent forms of social life. However, its occurrence in less derived social systems and thus its role in the early evolution of group-living remains unclear. Here, we investigated whether lining nests with feces is a form of social immunity against microbial growth in the European earwig Forficula auricularia, an insect with temporary family life and facultative maternal care. Results: Using a total of 415 inhibition zone assays, we showed that earwig feces inhibit the growth of two GRAM+ bacteria, two fungi, but not of a GRAM- bacteria. These inhibitions did not result from the consumed food or the nesting environment. We then demonstrated that the antimicrobial activity against fungus was higher in offspring than maternal feces, but that this difference was absent against bacteria. Finally, we showed that family interactions inhibited the antibacterial activity of maternal frass against one of the two GRAM+ bacteria, whereas they had no effect on the one of nymphal frass. By contrast, antifungal activities of the frass were independent of mother-offspring interactions. Conclusion: These results demonstrate that social immunity occurs in a species with simple and facultative social life, and thus shed light on the general importance of this process in the evolution of group-living. These results also emphasize that defecation can be under selection for other life-history traits than simple waste disposal.背景：社会性动物具备针对病原体发起社会防御（social immunity）的独特能力。近数十年来，学界已针对具有专性且永久性社会生活形式的物种，对社会免疫展开了大量研究。然而，社会免疫在低衍化社会系统中的存在情况，及其在群居生活早期演化中所扮演的角色仍不明朗。本研究以具有临时家庭生活与兼性育幼行为的欧洲球螋（Forficula auricularia）为研究对象，探究其以粪便铺垫巢穴是否属于一种抵御微生物生长的社会免疫策略。 结果：本研究共开展415次抑菌圈试验（inhibition zone assays），结果显示球螋粪便可抑制2种革兰氏阳性（Gram-positive）细菌与2种真菌的生长，但无法抑制1种革兰氏阴性（Gram-negative）细菌的增殖。上述抑菌效果并非来自受试食物或筑巢环境。随后研究发现，若虫粪便针对真菌的抗菌活性高于母虫粪便，但这一差异在针对细菌的抗菌活性中并不存在。最后，本研究证实，亲子互动会抑制母虫粪便对其中1种革兰氏阳性细菌的抗菌活性，但对若虫粪便的抗菌活性无影响。与之相反，虫粪的抗真菌活性不受亲子互动的影响。 结论：本研究结果证实，社会免疫存在于具有简单兼性社会生活的物种中，从而阐明了该过程在群居生活演化中的普遍重要性。本研究同时表明，昆虫的排便行为所受的选择压力，可源于除简单废物处置之外的其他生活史性状。