Data from: Task specialization in two social spiders, Stegodyphus sarasinorum (Eresidae) and Anelosimus eximius (Theridiidae).

Understanding the social organization of group living organisms is crucial for the comprehension of the underlying selective mechanisms involved in the evolution of cooperation. Division of labour and caste formation is restricted to eusocial organisms, but behavioural asymmetries and reproductive skew is common in other group living animals. Permanently social spiders form highly related groups with reproductive skew and communal brood care. We investigated task differentiation in non-reproductive tasks in two permanently and independently derived social spider species asking the following questions: Do individual spiders vary consistently in their propensity to engage in prey attack? Are individual spiders’ propensities to engage in web maintenance behaviour influenced by their previous engagement in prey attack? Interestingly, we found that both species showed some degree of task specialization, but in distinctly different ways: Stegodyphus sarasinorum, showed behavioural asymmetries at the individual level, i.e. individual spiders that had attacked prey once were more likely to attack prey again, independent of their body size or hunger level. In contrast, Anelosimus eximius showed no individual specialization, but showed differentiation according to life stage, where adult and subadult females were more likely to engage in prey attack than were juveniles. We found no evidence for division of labour between prey attack and web maintenance. Different solutions to achieve task differentiation in prey attack for the two species studied here suggest an adaptive value of task specialization in foraging for social spiders.

解析群居生物的社会组织结构，对于理解合作演化背后的选择机制至关重要。劳动分工与品级分化仅见于真社会性生物（eusocial organisms），但行为不对称与生殖偏斜（reproductive skew）现象在其他群居动物中较为普遍。永久社会性蜘蛛（permanently social spiders）会形成高度亲缘的群体，兼具生殖偏斜与共同育幼行为。本研究针对两种独立起源的永久社会性蜘蛛物种，探究其非繁殖任务中的任务分化情况，提出如下研究问题：个体蜘蛛参与猎物攻击的倾向是否存在稳定差异？个体蜘蛛开展结网维护行为的倾向，是否会受其此前参与猎物攻击的经历影响？有趣的是，本研究发现两个物种均存在一定程度的任务特化，但二者的特化模式截然不同：Stegodyphus sarasinorum在个体层面呈现行为不对称性——曾发起过一次猎物攻击的蜘蛛，后续再次发起攻击的概率更高，且该现象与其体型或饥饿水平无关。与之相反，Anelosimus eximius不存在个体层面的任务特化，而是按照生命阶段产生行为分化：成年与亚成年雌性个体发起猎物攻击的概率显著高于幼体。本研究未发现猎物攻击与结网维护之间存在劳动分工的证据。本研究中两个物种在猎物攻击任务分化上采用的不同策略，表明任务特化对于群居蜘蛛的觅食行为具有适应性价值。