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（division of labour）与品级形成（caste formation）仅局限于真社会性（eusocial）生物，但行为不对称与生殖偏斜（reproductive skew）在其他群居动物中颇为常见。永久社会性蜘蛛会形成具有高度亲缘关系的群体，兼具生殖偏斜与集体育幼行为。我们针对两种独立起源的永久社会性蜘蛛物种，探究其非生殖任务中的任务分化（task differentiation）情况，提出如下研究问题：单个蜘蛛在参与猎物攻击的倾向上是否存在稳定差异？单个蜘蛛参与结网维护（web maintenance）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，我们发现两个物种均存在一定程度的任务特化（task specialization），但分化模式截然不同：Stegodyphus sarasinorum在个体层面表现出行为不对称，即曾发起过一次猎物攻击的蜘蛛，更有可能再次参与猎物攻击，且该规律不受其体型或饥饿水平的影响。与之相反，Anelosimus eximius并未表现出个体层面的特化，而是依据生命阶段出现行为分化：成年与亚成体雌性蜘蛛参与猎物攻击的概率显著高于幼体蜘蛛。我们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中采取不同的分化策略，这表明任务特化对于社会性蜘蛛的觅食（foraging）行为具有适应价值。