Data from: Evolution of cellular architecture and function of the hippocampus: Insights from the artificial selection experiment

Inter-specifically, mammalian species having larger brains built of more numerous neurons have higher cognitive abilities (CA), but at the expense of higher metabolic costs. It is unclear, however, how this pattern emerged, since evolutionary mechanisms act intra-specifically, not inter-specifically. Here we tested the existence of the above pattern at the species level in the hippocampus- the brain structure underlying CA. We used the experimental evolution model system consisting of lines of laboratory mice divergently selected for basal metabolic rate (BMR) - a trait implicated in the evolution of brain size, its metabolic costs and CA. Selection on BMR did not affect hippocampus size. Yet, the high BMR mice had superior CA and manifested increased neuronal density, higher cytochrome C oxidase density (indexing metabolic costs of neuronal activity) and dendritic spine density (indexing connectivity between neurons). Thus, our study calls into question generality of patterns of the evolution of CA apparent interspecifically. At the species level increased CA may arise through re-arrangement of the architecture and function of neurons, without a conspicuous increase of their size.