Department of Ecology and Evolutionary Biology, University of Tennessee, 569 Dabney Hall, Knoxville, TN 37996, USA.
Mol Ecol. 2010 Feb;19(4):810-8. doi: 10.1111/j.1365-294X.2010.04523.x. Epub 2010 Jan 14.
The evolution of sociality remains a challenge in evolutionary biology and a central question is whether association between kin is a critical factor favouring the evolution of cooperation. This study examines genetic structure of Anelosimus studiosus, a spider exhibiting polymorphic social behaviour. Two phenotypes have been identified: an 'asocial' phenotype with solitary female nests and a 'social' phenotype with multi-female/communal nests. To address the questions of whether these phenotypes are differentiated populations and whether cooperative individuals are closely related, we used microsatellites to analyse individuals from both communal and solitary nests. We found no evidence of differentiation between social and solitary samples, implying high rates of interbreeding. This is consistent with the hypothesis that these phenotypes coexist as a behavioural polymorphism within populations. Pairwise relatedness coefficients were used to test whether cooperating individuals are more closely related than expected by chance. Pairwise relatedness of females sharing communal webs averaged 0.25, the level expected for half-siblings and significantly more closely related than random pairs from the population. Solitary females collected at similar distances to the communal spider pairs were also more closely related than expected by chance (mean relatedness = 0.18), but less related than social pairs. These results imply that low dispersal contributes to increase likelihood of interaction between kin, but relatedness between social pairs is not explained by spatial structure alone. We propose that these phenotypes represent stages in the evolution of sociality, where viscous population structure creates opportunities for kin selection and cooperation is favoured under certain environmental conditions.
社会性的进化仍然是进化生物学中的一个挑战，其中一个核心问题是，亲缘关系是否是促进合作进化的关键因素。本研究调查了表现出多态社会行为的蜘蛛 Anelosimus studiosus 的遗传结构。已经确定了两种表型：一种是具有独居雌性巢穴的“非社会性”表型，另一种是具有多雌性/群居巢穴的“社会性”表型。为了解决这些表型是否是分化的群体以及合作个体是否密切相关的问题，我们使用微卫星分析了来自群居和独居巢穴的个体。我们没有发现社会和独居样本之间存在分化的证据，这意味着存在大量的杂交。这与这些表型作为种群内的行为多态性共存的假设是一致的。成对相关系数用于检验合作个体是否比随机个体更密切相关。共享群居网的雌性之间的成对相关系数平均为 0.25，这是半同胞的预期水平，并且比种群中的随机对更密切相关。从与群居蜘蛛对相似距离处收集的独居雌性也比随机对更密切相关（平均相关系数为 0.18），但与社会对的相关性较低。这些结果表明，低扩散有助于增加亲缘个体之间相互作用的可能性，但社会对之间的亲缘关系不能仅用空间结构来解释。我们提出，这些表型代表社会性进化的阶段，其中粘性种群结构为亲缘选择创造了机会，并且在某些环境条件下合作是有利的。
