Modifying ancestral regulatory mechanisms can be a source of evolutionary novelty. Bees in small-colony, dominance-based societies typically show a link between size and aggression: larger bees are more aggressive. This led to the hypothesis that this size-aggression link is a characteristic of ancestral solitary bees that has acquired a novel function in the evolutionary transition from solitary to social behavior. Here we test the central prediction of this hypothesis, that size is linked to aggression in an ancestrally solitary bee. We use the sweat bee Nomia melanderi (Hymenoptera, Halictidae) in the subfamily Nomiinae, which is sister to the social sweat bees, all of which are in the subfamily Halictinae. We measured aggression using a standardized behavioral assay (circle tube) in which two bees were placed together and allowed to interact. We used three treatments: size matched small bees, size matched large bees, and one large bee paired with one small bee. We found no link between ovary size and aggression, but because we used only reproductively active bees we may not have had sufficient variation to detect such a link. Across treatments, body size negatively correlated with aggression. There were no differences between large and small bees in the matched treatments, but in the mixed treatment, small bees were more aggressive than large bees. This supported our prediction of a size-aggression link, although the link was in the opposite direction seen in social bees. Moreover, our data show that even solitary bees can modulate their aggression in response to social context and highlight the importance of studying related solitary species to understand the evolutionary origins of sociality.

中文翻译：

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小体型与孤独汗蜂 Nomia melanderi（膜翅目，Halictidae）的攻击性增加有关

修改祖先的调节机制可能是进化新颖性的一个来源。小蜂群、以支配地位为基础的社会中的蜜蜂通常表现出体型和攻击性之间的联系：较大的蜜蜂更具攻击性。这导致了这样一种假设，即这种大小与攻击性的联系是祖先独居蜜蜂的一个特征，它在从独居行为到社会行为的进化转变中获得了一种新的功能。在这里，我们测试了这一假设的核心预测，即体型与祖先独居蜜蜂的侵略性有关。我们使用 Nomia melanderi 亚科中的汗蜂 Nomia melanderi（膜翅目，Halictidae），它是社会汗蜂的姐妹，所有这些都属于 Halictinae 亚科。我们使用标准化的行为分析（圆管）来测量攻击性，其中将两只蜜蜂放在一起并允许相互作用。我们使用了三种处理方式：大小匹配小蜜蜂，大小匹配大蜜蜂，一只大蜜蜂与一只小蜜蜂配对。我们发现卵巢大小和攻击性之间没有联系，但因为我们只使用了繁殖活跃的蜜蜂，我们可能没有足够的变异来检测这种联系。在整个治疗过程中，体型与攻击性呈负相关。在匹配处理中，大蜜蜂和小蜜蜂之间没有差异，但在混合处理中，小蜜蜂比大蜜蜂更具攻击性。这支持了我们对体型-攻击性联系的预测，尽管这种联系与在社会蜜蜂中看到的方向相反。而且，