On the evolution of group-living in the New World cursorial hystricognath rodents

We used the comparative method to examine the evolutionary causesof group-living in the New World cursorial hystricognath rodents.To do so, we used the available literature to collect informationon behavioral (group size, burrow digging), ecological (amountof plant cover in the habitat), and life history (body mass,time to sexual maturity) variables, along with phylogeneticrelationships of these rodents. We analyzed these variablesin the context of three major hypotheses. A first explanationposes that rodents live in groups to reduce the energy neededin the construction of their burrows. A second hypothesis suggeststhat grouped rodents increase their ability to detect and escapefrom predators. A third possibility states that group-livingis adopted by rodents to provide extra parental care to theiroffspring. Our comparative analysis revealed that across speciesvariation of group size is, to some extent, influenced by bodysize, and by the habit of burrow digging. Thus, large sizedrodent species that actively dig their own burrows form largergroup sizes than small sized species that do not dig burrows.In contrast, across species variation of group size was notinfluenced by differences in the amount of plant cover in thehabitat (an indirect measure of predatory risk), or by differencesin the time to first reproduction (a measure of parental caregiven). Therefore, group-living among the New World histricognathrodents seems more linked to a strategy aimed to reduce theirburrowing cost than to a strategy aimed to reduce their predatoryrisk, or to extend their parental investment.