An alternative pathway to eusociality: exploring the molecular and functional basis of fortress defense

Some animals express a form of eusociality known as 'fortress defense', in which defense rather than brood care is the primary social act. Aphids are small plant-feeding insects, but like termites, some species express division of labor and castes of aggressive juvenile 'soldiers'. What is the functional basis of fortress defense eusociality in aphids? Previous work showed that the acquisition of venoms might be a key innovation in aphid social evolution. We show that the lethality of aphid soldiers derives in part from the induction of exaggerated immune responses in insects they attack. Comparisons between closely-related social and non-social species identified a number of secreted effector molecules that are candidates for immune modulation, including a convergently-recruited protease described in unrelated aphid species with venom-like functions. These results suggest that aphids are capable of antagonizing conserved features of the insect immune response, and provide new insights ...部分动物演化出一类被称为‘堡垒防御（fortress defense）’的真社会性（eusociality）策略，其核心社会行为以防御为主，而非育幼。蚜虫（aphids）是小型植食性昆虫，与白蚁类似，部分蚜虫物种存在劳动分工与具有攻击性的幼态“士兵”品级。蚜虫的堡垒防御型真社会性，其功能基础究竟是什么？既往研究表明，毒液的获得或许是蚜虫社会演化历程中的一项关键创新事件。本研究证实，蚜虫士兵的致死性部分源于其诱导了被攻击昆虫的过度免疫应答。通过对亲缘关系相近的社会性与非社会性蚜虫物种开展对比分析，本研究鉴定出多种可作为免疫调节候选因子的分泌效应分子（secreted effector molecules），其中包含在非亲缘蚜虫物种中被发现、具有毒液样功能的趋同招募蛋白酶（convergently-recruited protease）。上述研究结果表明，蚜虫能够拮抗昆虫免疫反应的保守特征，同时为该领域的研究提供了全新的视角……