Phylogeny modulates the effects of ecological conditions on group living across hystricognath rodents

• We provide the first report on loss of sociality across the phylogeny in hystricognath rodents.
• Our results support an early origin for sociality in Old World Phiomorpha and New World Caviomorpha.
• We used new phylogenetic statistical methods, molecular phylogenies and a large-scale behavioural database.
• Our results revealed frequent correlations between habitat use and group living in hystricognath rodents.
• Our revised use of phylogenetic information should revive interest in Tinbergen's important fourth question.

The evolution of group living in animals has been linked both to ecological and phylogenetic drivers or constraints. However, available evidence supporting each factor remains equivocal. In this study, we evaluated the influence of both scenarios across 98 species of hystricognath rodents using phylogenetic approaches that included a statistical model of trait evolution. We first estimated the hypothetical ancestral forms of several clades within the hystricognath phylogeny. Secondly, we examined evolutionary correlations between habitat conditions in terms of vegetation cover and group living to determine general macroevolutionary trends on social behaviour. Given the contrasting modes of life that characterize these rodents, we also examined whether subterranean habits influence group living. Our results support the hypothesis that group living in Old World Phiomorpha and New World Caviomorpha had an early origin. The best-fitted and well-supported model of evolution for group living was the equal rate model, implying an equal rate of gains and losses of group living. Logistic regression analyses that included phylogenetic relationships revealed significant correlation between habitats used (i.e. vegetation cover) and absence or presence of group living. The loss of group living across the phylogeny was associated with the use of closed habitat conditions. No association was found between changes in group living and subterranean mode of life. We conclude that ancestor–descendant relationships mediate the effect of changes in habitat use on the evolution of group living across -hystricognath rodents.