The enlarged brains of homeotherms bring behavioural advantages, but also incur high energy expenditures. The ‘Expensive Brain’ (EB) hypothesis posits that the energetic costs of the enlarged brain and the resulting increased cognitive abilities (CA) were met either by increased energy turnover or reduced allocation to other expensive organs, such as the gut.

We tested the EB hypothesis by analyzing correlated responses to selection in an experimental evolution model system, which comprises line types of laboratory mice selected for high or low basal (BMR), or high maximum (VO_2max) metabolic rates. The traits are implicated in the evolution of homeothermy, having been pre-requisites for the encephalisation and exceptional CA of mammals, including humans. High-BMR mice had bigger guts, but not brains, than mice of other line types. Yet, they were superior to the other line types in the cognitive tasks carried out in both reward and avoidance learning contexts. Furthermore, the high-BMR mice had higher neuronal plasticity (indexed as the long-term potentiation, LTP) than their counterparts. Our data indicate that the evolutionary increase of CA in mammals was initially associated with increased BMR and brain plasticity. It was also fueled by an enlarged gut, which was not traded off for brain size.

All information on data collection and processing is provided in the manuscript and Supplementary Materials.

Goncerzewicz_et_al_data.xls

File contains raw data on individual measurements of Basal Metabolic Rate (BMR), body and internal organ masses (including brain), assessments of locomotor activity and reward-motivated discrimination learning along with data long-term potentiation (LTP), a classical model for investigation of activity-dependent synaptic plasticity. Detailed description of all measured variables is provided in Spreadsheet legend.