No evidence for larger brains in cooperatively breeding cichlid fishes

Abstract: The social brain hypothesis posits that frequent social interactions, characteristic of group living species, select for greater socio-cognitive abilities and the requisite neural machinery. An extension of the social brains hypothesis, known as the cooperative breeding brain hypothesis, postulates that cooperatively breeding species, which live in stable social groups and provide allocare, face particularly pronounced cognitive demands as they must recognize, remember, and differentially respond to multiple group members. These socio-cognitive challenges are thought to have selected for increased cognitive capacity, supported by a bigger brain. In order to test the prediction that cooperative breeders have larger brains, we performed a phylogenetically-controlled comparison of the whole brain masses of adult males from eight closely related species of cooperatively and independently breeding Lamprologine cichlid species collected from Lake Tanganyika. In order to expand our sample size, we repeated this analysis including data for eight additional Lamprologine species drawn from the published literature. Controlling for body size and phylogeny, we did not find that the cooperative breeding species had larger brains in either our field collected dataset or in the expanded dataset including data points from the literature. This study adds to a growing body of literature from other taxa casting doubt on the cooperative breeding brain hypothesis.