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

Body mass of wild ring-tailed lemurs in Berenty Reserve, Madagascar, with reference to tick infestation: a preliminary analysis

“…This type of sexual dimorphism has been discussed from the viewpoints of ecology, physiology, and life history (Masterson and Hartwig 1998;Plavcan 2001). In particular, it has been disputed whether such a dimorphism is a natural consequence of sexual selection (i.e., male-male competition for access to mates) (Plavcan and van Schaik 1997).…”

Levels of Intraspecific Variation Within the Catarrhine Skeleton

“…The facial, mandibular, bicanine, palatal, and nuchal regions vary most because of dimorphic muscle attachments, whereas the orbits, the cranial vault, and basicranium are relatively unaffected (Plavcan 2002;Wood and Lieberman 2001). Postcranial skeletal dimorphism is generally the result of body mass dimorphism (Plavcan 2001) and is manifest in differences of size, muscle attachments, and robusticity. The exception to this rule is dimorphism in pelvic morphology, which is adapted to parturition in the female (Martin et al 1994).…”

“…There is also much evidence that crania are subject to one particular form of intraspecific variation: sexual dimorphism. Most anthropoid males are larger than females of the same species (Martin et al 1994), and considerable canine dimorphism is also common (Plavcan 2001). Within the skeleton, regions with muscle attachments are often strongly sexually dimorphic.…”

“…Within the skeleton, regions with muscle attachments are often strongly sexually dimorphic. A larger animal with larger muscles will experience higher strains and increased osteogenic change, which can increase dimorphism during an organism's life (Plavcan 2001). The facial, mandibular, bicanine, palatal, and nuchal regions vary most because of dimorphic muscle attachments, whereas the orbits, the cranial vault, and basicranium are relatively unaffected (Plavcan 2002;Wood and Lieberman 2001).…”

A morphometric analysis of the Japanese macaque (Macaca fuscata) mandibular cheek teeth from the Torihama Shell-midden, Early Jomon Period, Fukui Prefecture, Japan

“…Macaques have strong sexual dimorphism in the ''canine/premolar complex'' (Wood 1976;Plavcan 2001). The difference is especially noted for pigtailed macaques (Macaca nemestrina) where the measurements of Cmd do not overlap between males and females (Swindler 2002).…”