Some cognitive abilities are suggested to be the result of a complex social life, allowing individuals to achieve higher fitness through advanced strategies. However, most evidence is correlative. Here, we provide an experimental investigation of how group size and composition affect brain and cognitive development in the guppy (Poecilia reticulata). For six months, we reared sexually mature females in one of three social treatments: a small conspecific group of three guppies, a large heterospecific group of three guppies and three splash tetras (Copella arnoldi) – a species that co-occurs with the guppy in the wild, and a large conspecific group of six guppies. We then tested the guppies’ performance in self-control (inhibitory control), operant conditioning (associative learning) and cognitive flexibility (reversal learning) tasks. Using X-ray imaging, we measured their brain size and major brain regions. Larger groups of six individuals, both conspecific and heterospecific groups, showed better cognitive flexibility than smaller groups, but no difference in self-control and operant conditioning tests. Interestingly, while social manipulation had no significant effect on brain morphology, relatively larger telencephalons were associated with better cognitive flexibility. This suggests alternative mechanisms beyond brain region size enabled greater cognitive flexibility in individuals from larger groups. Although there is no clear evidence for the impact on brain morphology, our research shows that living in larger social groups can enhance cognitive flexibility. This indicates that the social environment plays a role in the cognitive development of guppies.

中文翻译：

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社会复杂性会影响 Poecilid 鱼的认知能力，但不会影响大脑结构

一些认知能力被认为是复杂社会生活的结果，使个人能够通过先进的策略获得更高的适应性。然而，大多数证据都是相关的。在这里，我们对群体规模和组成如何影响孔雀鱼（Poecilia reticulata）的大脑和认知发展进行了实验研究。在六个月的时间里，我们用三种社会处理方式中的一种饲养性成熟的雌性：由三只孔雀鱼组成的小型同种群体，由三只孔雀鱼组成的大型异种群体和三只水斑四孔雀鱼（Copella arnoldi）——一种与孔雀鱼共存的物种。野生的，还有一大群六只孔雀鱼。然后，我们测试了孔雀鱼在自我控制（抑制控制）、操作条件反射（联想学习）和认知灵活性（逆向学习）任务中的表现。使用 X 射线成像，我们测量了他们的大脑大小和主要大脑区域。由六人组成的较大群体，无论是同种群体还是异种群体，都比较小群体表现出更好的认知灵活性，但在自我控制和操作性条件反射测试中没有差异。有趣的是，虽然社交操纵对大脑形态没有显着影响，但相对较大的端脑与更好的认知灵活性相关。这表明大脑区域大小之外的其他机制可以使来自较大群体的个体具有更大的认知灵活性。尽管没有明确的证据表明对大脑形态的影响，但我们的研究表明，生活在更大的社会群体中可以增强认知灵活性。这表明社会环境在孔雀鱼的认知发展中发挥着作用。