ONTOGENIC VARIATION IN SMALL-BODIED NEW-WORLD PRIMATES - IMPLICATIONSFOR PATTERNS OF REPRODUCTION AND INFANT CARE

This paper explores relations of ontogeny, life history strategies and patterns of infant care in 11 species of small-bodied New World monke ys. Analysis of these data suggests that differences in the social sys tems of Aotus, Callicebus, Saimiri, Callimico, Saguinus, Leontopithecu s, Cebuella and Callithrix are closely tied to both the costs of repro duction and to the ontogenetic requirements of maturing young. In Saim iri, both rapid prenatal body weight and perinatal brain growth result in relatively high metabolic costs to breeding females. These costs, coupled with minimal nonmaternal assistance in caregiving, appear to f avor a reproductive strategy that limits offspring production to a sin gle birth at 2-year intervals. In contrast, tamarins and marmosets are capable of producing twins twice in the same year. Prenatal investmen t in each offspring is relatively low, and the potentially high postna tal costs of nursing 2 infants are minimized by the evolution of a soc ial system involving extensive extramaternal caregiving. Cooperative i nfant care in callitrichins (tamarins and marmosets) serves to distrib ute the metabolic costs of infant ontogeny among several group members . Callimico is also characterized by a high reproductive output, with females capable of producing a single infant twice during the year. In fants continue to grow rapidly after weaning. Patterns of infant devel opment in Callimico are similar to those found in tamarins and marmose ts and support a close phylogenetic relationship among these taxa, Aot us and Callicebus are characterized by an alternative strategy. In the se taxa, a monogamous mating system is associated with paternal certai nty, male parental care, and provisioning of the young. The transfer o f male energetic resources to a single offspring allows night and titi monkeys to maintain a comparatively short interbirth interval (1 year ). Ecological and social factors, such as predation and feeding compet ition, do not appear to adequately explain much of the observed variat ion in infant development and preadult growth rates in these platyrrhi nes. Instead, reproductive strategies are strongly linked to ontogenet ic patterns and life histories.