Sexual dimorphism in primate evolution

Abstract

Sexual dimorphism is a pervasive phenomenon among anthropoid primates. Comparative analyses over the past 30 years have greatly expanded our understanding of both variation in the expression of dimorphism among primates, and the underlying causes of sexual dimorphism. Dimorphism in body mass and canine tooth size is familiar, as is pelage and "sex skin" dimorphism. More recent analyses are documenting subtle differences in the pattern of skeletal dimorphism among primates. Comparative analyses have corroborated the sexual selection hypotheses, and have provided a more detailed understanding of the relationship between sexual selection, natural selection, and mating systems in primates. A clearer picture is emerging of the relative contribution of various selective and nonselective mechanisms in the evolution and expression of dimorphism. Most importantly, recent studies have shown that dimorphism is the product of changes in both male and female traits. Developmental studies demonstrate the variety of ontogenetic pathways that can lead to dimorphism, and provide additional insight into the selective mechanisms that influence dimorphism throughout the lifetime of an animal. Evidence from the fossil record suggests that dimorphism probably evolved in parallel twice, and the dimorphism in some extinct hominoids probably exceeded that of any living primate. Our advances in understanding the behavioral/ecological correlates of dimorphism in living primates have not improved our ability to reconstruct social systems in extinct species on the basis of dimorphism alone, beyond the inference of polygyny or intense male-male competition. However, our understanding of the behavioral/ecological correlates of growth and development, and of the expression of dimorphism as a function of separate changes in male and female traits, offers great potential for inferring evolutionary changes in behavior over time

Wide faces or large canines? The attractive versus the aggressive primate

“…This suggests that male primates in species without dimorphic canines have proportionally broader, shorter faces relative to females, whereas male primates with highly dimorphic canines have relatively long faces that are not disproportionately broadened relative to females. Generally, in primates a more elongate face facilitates increased gape and the presence of large canines (Plavcan 2001). This observation is corroborated here by the significant correlation shown between superior FHT dimorphism and DI CHT .…”

Color in competition contexts in non-human animals

“…This suggests that male competition is important year-round in mandrills, but less so in rhesus. Competition appears to be lower overall in rhesus macaques, which are less sexually dimorphic than mandrills, in both body size and canine size (Plavcan, 2001), suggesting that males experience less direct competition over rank and mating access. In line with this, rank-related reproductive skew is far lower in rhesus than in mandrills (Berard, Nürnberg, Epplen, & Schmidtke, 1993;Dubuc, Muniz, Heistermann, Engelhardt, & Widdig, 2011;Widdig et al, 2004).…”

The Early Development of Gender Differences

“…The few exceptions are in species in which roles may be partially mixed and the sexes have less notable differences, and which more often have mating systems characterized as monogamous (Jarman 1983, Plavcan 2001. The primate order includes a relatively large number of monogamous species, often characterized by some level of male parental investment (Fuentes 1998).…”