Complex cooperative breeders: Using infant care costs to explain variability in callitrichine social and reproductive...

The influence of ecology on social behavior and mating strategies is one of the central questions in behavioral ecology and primatology. Callitrichines are New World primates that exhibit high behavioral variability, which is widely acknowledged, but not always systematically researched. Here, I examine the hypothesis that differences in the cost of infant care among genera help explain variation in reproductive traits. I present an integrative approach to generate and evaluate predictions from this hypothesis. I first identify callitrichine traits that vary minimally and traits that are more flexible (e.g., have greater variance or norm of reaction), including the number of males that mate with a breeding female, mechanisms of male reproductive competition, number of natal young retained, and the extent of female reproductive suppression. I outline how these more labile traits should vary along a continuum of infant care costs according to individual reproductive strategies. At one end of the spectrum, I predict that groups with higher infant care costs will show multiple adult males mating and providing infant care, high subordinate female reproductive suppression, few natal individuals delaying dispersal, and increased reproductive output by the dominant female -with opposite predictions under low infant costs. I derive an estimate of the differences in ecological and physiological infant care costs that suggest an order of ascending costs in the wild: Cebuella, Callithrix, Mico, Callimico, Saguinus, and Leontopithecus. I examine the literature on each genus for the most variable traits and evaluate a) where they fall along the continuum of infant care costs according to their reproductive strategies, and b) whether these costs correspond to the ecophysiological estimates of infant care costs. I conclude that infant care costs can provide a unifying explanation for the most variable reproductive traits among callitrichine genera. The approach presented can be used to generate predictions and motivate researchers to unravel complexity in callitrichine social and reproductive behavior.