Brain size, gut size and cognitive abilities: the energy trade-offs tested in artificial selection experiment

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 (VO2max) 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-BM...