Collaborative Research: Social brains and solitary bees: A phylogenetic test of the effect of social behavior on brain evolution across multiple gains and losses of sociality

社交互动是如何决定大脑大小的？与其他动物生活在一个社会群体中，可能需要更大的大脑来应对维持社会关系的认知挑战。或者，社会群体中的动物的大脑可能更小，因为社会群体的成员可以一起工作，从而减少每个人面临的认知挑战。这项研究将测量群居蜜蜂和独居蜜蜂密切相关物种的大脑大小。社会合作在蜜蜂身上进化了多次，也曾多次失传：一些独居的蜜蜂是从社会祖先进化而来的。该项目还将测量蜜蜂大脑中与攻击性和繁殖有关的神经递质和激素的水平。科学家们仍然不清楚，即使是相对简单的大脑差异，也与复杂行为特征的进化有关。这项研究将利用蜜蜂的小大脑和许多不同的社会和独居物种之间的多重比较来研究生活在合作的社会群体中对大脑的影响。参与该项目的科学家将通过在他们的实验室实习来指导学生，并将撰写针对初中生和高中生的研究出版物版本，这些出版物将在网上免费提供，用于教育和推广。这个项目测试了社会合作的进化导致大脑尺寸增大的假设。这项研究的重点是测量蘑菇体(昆虫大脑的一个区域)的体积以及群居和独居蜜蜂大脑的生物胺的变化。研究人员把重点放在汗蜂(汗蜂科)上，因为这个群体是祖先孤独的，有三个社会性的进化起源和来自社会支系内部的多个进化损失。此外，许多物种具有社会多态，既表现出社交行为，也表现出独居行为。这允许进行多个系统发育上独立的社会-孤立比较。研究人员将重点放在蘑菇身体体积上，因为大脑的这一区域用于学习、记忆和感觉整合。他们测量生物性脑胺，因为这些化学物质参与调节攻击性、社会性和生殖行为，因此很可能参与社会合作的进化。最后，他们测试脑胺水平的变化是否与大脑大小的变化有机械联系，并测量与社会行为相关的胺受体密度的变化。这项工作使用系统发育比较方法、脑体积的共聚焦显微镜测量、胺滴度的高效液相色谱(HPLC)测量以及胺反应神经元的抗体染色来测试社会合作的进化得失如何影响大脑。这项工作解决了公众广泛关注的问题--大脑进化和合作。作为该项目更广泛影响的一部分，研究人员将与专业编辑合作，为他们的研究创建开放获取的改编版本，用于课堂或其他教育或宣传目的。他们还将在五个不同的机构培训研究生和本科生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

How do social interactions drive brain size? Living in a social group with other animals may require a bigger brain in order to deal with the cognitive challenge of maintaining social relationships. Alternatively, animals in social groups may have smaller brains because members of social groups can work together, thus reducing the cognitive challenge faced by each individual. This research will measure brain size in closely related species of social and solitary bees. Social cooperation has evolved many times in bees, and has also been lost many times: some solitary bees evolved from social ancestors. This project will also measure levels of neurotransmitters and hormones in bee brains that are associated with aggression and reproduction. Scientists still do not have a clear understanding of how even relatively simple brain differences are associated with the evolution of complex behavioral traits. This research will use the small brains of bees and the multiple comparisons between many different social and solitary species to investigate how living in a cooperative social group affects the brain. The scientists involved in the project will mentor students through internships in their labs, and will write versions of their research publications aimed at middle- and high-school aged students that will be made freely available on the web for education and outreach. This project tests the hypothesis that the evolution of social cooperation leads to increased brain size. This research focuses on measuring changes in the volume of the mushroom body (an area of the insect brain), and biogenic amines of the brains of social and solitary bees. The researchers focus on the sweat bees (Halictidae) because this group is ancestrally solitary with three evolutionary origins of sociality and multiple evolutionary losses from within the social clades. Also, many species are socially polymorphic, exhibiting both social and solitary behavior. This allows for multiple phylogenetically independent social-solitary comparisons. The researchers focus on mushroom body volume because this area of the brain is used for learning, memory, and sensory integration. They measure biogenic brain amines because these chemicals are involved in regulating aggressive, social, and reproductive behavior, and thus likely involved in the evolution of social cooperation. Lastly, they test whether changes in levels of brain amines are mechanistically linked to changes in brain size, and also measure changes in amine receptor density associated with social behavior. This work uses a phylogenetic comparative approach, confocal microscopy measurements of brain volume, high performance liquid chromatography (HPLC) measurements of amine titers, and antibody staining of amine-reactive neurons to test how evolutionary gains and losses of social cooperation affect the brain. This work addresses issues of broad public appeal - brain evolution and cooperation. As part of the broader impacts of this project, researchers will work with professional editors to create open-access adaptations of their studies for use in classrooms or other educational or outreach purposes. They will also train graduate and undergraduate students across five different institutions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.