Evolution of burrowing and associated behavioral traits in Lagomorphs

Burrowing is a complex behavior that has evolved repeatedly across animal lineages, yet its evolutionary origins and ecological correlates remain poorly understood in many mammalian groups. The order Lagomorpha, comprising pikas (Ochotonidae), rabbits and hares (Leporidae) exhibits remarkable diversity in lifestyle, sociality, and life history, making it an ideal system to study the evolution of burrowing behavior. Here, we reconstruct the most comprehensive dated phylogeny of Lagomorphs to date, encompassing 84 of 102 extant species, including newly sequenced genomes of Ochotona nubrica and O. ladacensis. Using ancestral state reconstruction and phylogenetically informed comparative analyses, we examine how burrowing behavior relates to morphology, climate, habitat, sociality, and fecundity. Our results reveal that burrowing evolved multiple times independently within Lagomorphs, with the ancestral state of Ochotonids inferred as burrowing and that of Leporids as semi-fossorial or form-dwelling. Contrary to expectations, burrowing species did not show distinct hind-limb adaptations or associations with extreme or variable climates. However, burrowing behavior was significantly correlated with sociality, and both burrowing and social species exhibited higher fecundity, suggesting an energetic and reproductive advantage linked to group-living in fossorial taxa. These findings highlight a recurrent evolutionary association between burrowing, sociality, and reproductive investment: the burrowing, sociality and fecundity triangle. This underscores the importance of integrating behavioral and ecological data to understand the adaptive evolution of lifestyle traits in mammals.