Down a rabbit hole: Burrowing behaviour and larger home ranges are related to larger brains in Leporids

Abstract

Studies on the evolution of brain size variation usually focus on large clades encompassing broad phylogenetic groups. This risks the introduction of ‘noise’ in the results, often obscuring effects that might be detected in less inclusive clades. In the current study we focus on a sample of 18 species of leporids from 60 individuals, and test five different hypotheses related to brain size (approximating it from endocranial volume) evolution in mammals. This includes the evolution of the whole brain, as well as the olfactory bulb. We also address a pervasive issue in comparative phylogenetic studies by dealing with missing data via multiple phylogenetic imputations as to conserve the full sample size for all subsequent analyses. Using leporids as a sample allows for the coverage of good body size diversity while avoiding the issue of too wide taxonomic sampling. Our analyses show that home range and burrowing behaviour are the only predictors of leporid brain size variation in this clade. Additionally, the evolutionary increase in litter size (often found as a constraint in brain size evolution) is related to increased temperature seasonality therefore tentatively masking the constraining effect of litter size on brain size in leporids. Unreasonable estimations of phylogenetic signal (Pagel’s lamba) additionally warrant caution when using small sample sizes in comparative studies.