Social behavior has been predicted to select for increased neural investment (the social brain hypothesis) and also to select for decreased neural investment (the distributed cognition hypothesis). Here, we use two related bees, the social Augochlorella aurata (Smith) (Hymenoptera: Halictidae) and the related Augochlora pura (Say), which has lost social behavior, to test the contrasting predictions of these two hypotheses in these taxa. We measured the volumes of the mushroom body (MB) calyces, a brain area shown to be important for cognition in previous studies, as well as the optic lobes and antennal lobes. We compared females at the nest foundress stage when both species are solitary so that brain development would not be influenced by social interactions. We show that the loss of sociality was accompanied by a loss in relative neural investment in the MB calyces. This is consistent with the predictions of the social brain hypothesis. Ovary size did not correlate with MB calyx volume. This is the first study to demonstrate changes in mosaic brain evolution in response to the loss of sociality.

中文翻译：

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社交性的丧失伴随着汗蜂 Agochlora Pura（膜翅目：Halictidae）蘑菇体体积的神经投资减少

社会行为被预测会选择增加神经投资（社会大脑假说），也选择减少神经投资（分布式认知假说）。在这里，我们使用了两种相关的蜜蜂，社会化的Augochlorella aurata (Smith)（膜翅目：Halictidae）和相关的Augochlora pura(Say), 已经失去了社会行为，以测试这些分类群中这两个假设的对比预测。我们测量了蘑菇体 (MB) 花萼的体积，这个大脑区域在之前的研究中被证明对认知很重要，以及视叶和触角叶。我们在筑巢阶段比较了雌性，此时两个物种都是独居的，这样大脑的发育就不会受到社会互动的影响。我们表明，社交性的丧失伴随着 MB 花萼的相对神经投资的丧失。这与社会大脑假说的预测一致。子房大小与 MB 花萼体积无关。这是第一项证明马赛克大脑进化因社会性丧失而发生变化的研究。