Ontogeny and the Evolution of Body Size Dimorphism in Primates - Leigh - 1995

Recent research shows that anthropoid primates exhibit considerable variation in the ontogeny of body size sexual dimorphism. In general, there are two basic patterns by which primates become sexually dimorphic. Dimorphism can develop through differences in the rate of body weight growth. In such species, males tend to exhibit very obvious pubertal or adolescent growth spurts. Although males of these species typically grow for longer periods of time than females, the duration difference in growth often contributes little to the total resultant dimorphism. A second ontogenetic pathway to sexual dimorphism mainly involves sex differences in the duration of the growth period (bimaturism). In these taxa, males typically grow for longer periods of time than females, but there are often only slight sex differences in growth rates. In species that are not sexually dimorphic as adults, there is usually little variation between sexes in growth rate and duration. Investigation of these alternative ontogenetic pathways indicates that multiple factors influence the ontogeny of sexual dimorphism in primates. Interspecific variation in female ontogeny, which can be quite substantial, corresponds to life history variation. Specifically, dietary and reproductive correlates of female ontogeny are apparent. In addition, differences among species in the degree and kind of interfemale competition relate to ontogenetic diversity. Variation in male ontogeny covaries most closely with intermale mating competition. Ontogenetic variation among species in male growth is structured according to the kinds of risks that males encounter. Specifically, prolonged growth with bimaturism is related to risks of intermale competition that increase steadily with age. On the other hand, risks encountered by males seem to change rapidly in those species that exhibit large male growth spurts, limited bimaturism, and high dimorphism. These analyses demonstrate the importance of ontogenetic and life history information in explaining the complex phenomenon of primate sexual dimorphism.

Keywords

Monkeys and apes - Growth - Development - Sexual selection

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