Brain size, ecology and sociality: a reptilian perspective

It is often hypothesized that larger brains evolved to deal with environmental complexity, by means of enhanced cognition and behavioural flexibility. Decades of research have tried to relate relative brain size to either habitat or social complexity, but often with conflicting results. Which selective pressures favour larger brains and whether they act in the same way in different taxa is unclear, especially given that the majority of studies focused on either mammals or birds. We present the first large-scale comparative study investigating the effect of habitat and social complexity on evolution of brain size in Squamata (lizards and snakes), using a dataset of 171 species. Our analyses confirmed earlier findings that both the degree of limb reduction and the biogeographical origin of a species affect relative brain size and should be controlled for. Habitat complexity had no effect on brain size, and solitary species had larger brains than social species. These results suggest that different selective forces might drive evolution of brain size in Squamata compared with other taxa. Future comparative studies should also consider using other, non-traditional, taxa. This will contribute to a more comprehensive understanding of how the vertebrate brain evolved.