Department of Bioscience, Aarhus University, 8000, Aarhus C, Denmark.
J Evol Biol. 2013 Mar;26(3):553-61. doi: 10.1111/jeb.12072. Epub 2013 Jan 3.
Reproductive partitioning is a key component of social organization in groups of cooperative organisms. In colonies of permanently social spiders of the genus Stegodyphus less than half of the females reproduce, while all females, including nonreproducers, perform suicidal allo-maternal care. Some theoretical models suggest that reproductive skew is a result of contest competition within colonies, leading to size hierarchies where only the largest females become reproducers. We investigated the effect of competition on within-group body size variation over six months in S. dumicola, by manipulating food level and colony size. We found no evidence that competition leads to increased size asymmetry within colonies, suggesting that contest competition may not be the proximate explanation for reproductive skew. Within-colony body size variation was high already in the juvenile stage, and did not increase over the course of the experiment, suggesting that body size variation is shaped at an early stage. This might facilitate task specialization within colonies and ensure colony-level reproductive output by early allocation of reproductive roles. We suggest that reproductive skew in social spiders may be an adaptation to sociality selected through inclusive fitness benefits of allo-maternal care as well as colony-level benefits maximizing colony survival and production.
生殖分工是合作生物群体社会组织的一个关键组成部分。在永久性社会性蜘蛛属 Stegodyphus 的群体中，不到一半的雌性进行繁殖，而所有的雌性，包括不繁殖的雌性，都会进行自杀式的异体亲代照顾。一些理论模型表明，生殖偏斜是群体内部竞争的结果，导致大小等级制度，只有最大的雌性才能成为繁殖者。我们通过操纵食物水平和群体大小，在六个月内调查了竞争对 S. dumicola 群体内身体大小变化的影响。我们没有发现竞争导致群体内体型不对称增加的证据，这表明竞争可能不是生殖偏斜的直接原因。群体内的身体大小变化在幼体阶段就已经很高，并且在实验过程中没有增加，这表明体型变化是在早期形成的。这可能有助于群体内的任务专业化，并通过早期分配生殖角色来确保群体水平的生殖产出。我们认为，社会性蜘蛛的生殖偏斜可能是一种通过异体亲代照顾的适合度利益以及最大化群体生存和繁殖的群体利益选择的社会性适应。
