Does sociality drive the evolution of communicative complexity? A comparative test with ground-dwelling sciurid alarm calls [La socialité dirige-t-elle l'évolution de la communication complexe? test comparatif des cris d'alarme chez les sciuridés terrestres].

Résumé

While sociality has been hypotesized to drive the evolution of communicative complexity, the relationship remains to be formally tested. We derived a continuous measure of social complexity from demographic data and use this variable to explain variation in alarm repertoire size in ground-dwelling sciurid rodents (marmots, Marmota spp., prairie dogs, Cynomys spp. and ground squirrels, Spermophilus spp.). About 40% of the variation in alarm call repertoire size was explained by social complexity in the raw data set. To determine the degree to which this relationship may have been influenced by historical relationships between species, we used five different phylogenetic hypotheses to calculate phylogenetically independent contrasts. Less variation was significantly explained in contrast-based analyses, but a general positive relationship remained. Social complexity explained more variation in alarm call repertoire size in marmots, while sociality explained no variation in repertoire size in prairie dogs and no variations in phylogenetically based analyses of squirrels. In most cases, substantial variation remained unexplained by social complexity. We acknowledge that factors other than social complexity, per se, may contribute to the evolution of alarm call repertoire size in sciurid rodents, and we discuss alternative evolutionary hypotheses that involve social complexity.