Sexual dimorphism in non-human primates

Sexual dimorphism in non-human primates has long been observed in the primate family, with numerous studies performed to document and explain the phenomenon. Recent studies have mainly used the technique of comparative analysis to examine both the variation in the expression of the dimorphism among primates and the fundamental causes of sexual dimorphismcite journal | author=Lindenfors P & Tullberg BS | year=1998 | title=Phylogenetic Analyses of Primate Size Evolution: The Consequences of Sexual Selection | journal=Biological Journal of the Linnean Society | volume=64 | pages=413–447 | doi=10.1111/j.1095-8312.1998.tb00342.x] . Primates usually have dimorphism in body mass [cite journal | author=Ralls, K | year=1976 | title=Mammals in Which Females are Larger Than Males | journal=The Quarterly Review of Biology | volume=51 | issue=2 | doi=10.1086/409310 | pages=245] [cite journal | author=Lindstedtand & Boyce | year=1985 | journal=Am Nat | volume=125 | pages=873 | doi=10.1086/284385 | title=Seasonality, Fasting Endurance, and Body Size in Mammals] and canine tooth size [cite journal | author=Frisch, J. E. | year=1963 | title=Sex-differences in the canines of the gibbon ("Hylobates lar") | journal = Primates | volume = 4 | issue = 2 | doi=10.1007/BF01659148 | pages=1] [cite journal | author=Kay, R. F. | year = 1975 | title = The functional adaptations of primate molar teeth | volume = 43 | issue = 2 | pages = 195–215] cite journal | author=Thorén, S., Lindenfors, P. & Kappeler, P. M. | year=2006 | title=Phylogenetic analyses of dimorphism in primates: Evidence for stronger selection on canine size than on body size | journal = Am J Phys Anthropol | volume = 130 | issue = 1 | pages = 50–59 | doi=10.1002/ajpa.20321] along with pelage and skin colour. [cite book | author=Crook | year=1972 | chapter=Sexual selection, dimorphism, and social organization in the primates | title=Sexual selection and the descent of man] The dimorphism in primates has been attributed to many factors:
*Mating system – Polygynous species are more sexually dimorphic than monogamous species, such as the New World monkeys.cite journal | author=Cheverud, J.M., Dow, M. M. & Leutenegger, W. | year=1985 | title=The quantitative assessment of phylogenetic constraints in comparative analyses: Sexual dimorphism in body weight among primates | journal = Evolution | volume = 39 | issue = 6 | pages = 1335–1351 | doi=10.2307/2408790] It is also associated with greater male gonadal investment than what is found in closely related monogamous species. [cite journal | author=Luetenegger, W. | year=1978 | title=Scaling of sexual dimorphism in body size and breeding system in primates | journal = Nature | volume = 272 | pages = 610–611 | doi=10.1038/272610a0] cite journal | author=Leutenegger, W. & Cheverud, J. M. | year=1982 | title=Correlates of sexual dimorphism in primates: Ecological and size variables | journal = International Journal of Primatology | volume = 3 | issue = 4 | doi=10.1007/BF02693740 | pages=387]
*Size – Larger species are more sexually dimorphic than smaller species.
*Habitat – Terrestrial species tend to be more sexually dimorphic than arboreal species. It is possible that male-male competition in terrestrial species is more dependent on body size.
*Diet – Frugivores, for reasons that are not clear, are slightly more sexually dimorphic than folivores. Energy may be less of a constraint. or maybe females may be more clumped around an area of fruit trees.

Comparative analyses have substantiated the sexual selection hypotheses, and have generated a more complete understanding of the relationship between sexual selection, natural selection, and mating systems in primates. Studies are helping to find the relative contribution of the various selective and non-selective mechanisms in sexual dimorphism evolution and expression. [cite journal | author=Plavcan, J.M. | year=2001 | title=Sexual dimorphism in primate evolution | journal = Am J Phys Anthropol. | volume = 33 | pages = 25–53 | doi=10.1002/ajpa.10011] These studies have shown that dimorphism is the product of changes in both male and female traitscite journal | author=Lindenfors P | year=2002 | title=Sexuall Antagonistic Selection on Primate Size | journal=Journal of Evolutionary Biology | volume=15 | pages=595–607 | doi=10.1046/j.1420-9101.2002.00422.x] . Ontogenic scaling, where relative extension of a common growth trajectory occurs, may show some insight into the relationship between sexual dimorphism and growth patterns.cite journal | author=O'Higgins, P. & Collard, M. | year=2002 | title=Sexual dimorphism and facial growth in papionin monkeys | journal=Journal of Zoology | volume=257 | issue=2 | pages=255–272 | doi=10.1017/S0952836902000857] There is some evidence from the fossil record that suggests that there was convergent evolution of dimorphism, and some extinct hominids probably exceeded dimorphism of any living primate.

exual dimorphism in the primate face

Sex-linked skeletal and dental variation in primates has been the focus of considerable anthropological and anatomical research since 2002. [cite journal | author=Schillaci, M. A. & Stallmann, R. R. | year=2005 | title=Ontogeny and sexual dimorphism in booted macaques ("Macaca ochreata") | journal = Journal of Zoology | volume = 267 | issue = 1 | pages = 19–29 | doi=10.1017/S0952836905007144] [cite journal | author=Blanco, M. B. & Godfrey, L. R. | year=2006 | title=Craniofacial sexual dimorphism in Alouatta palliata, the mantled howling monkey | journal=Journal of Zoology | volume=270 | issue=2 | pages=268–276] [cite journal | author=Elton, S. & Morgan, B.J. | year=2006 | title=Muzzle size, paranasal swelling size and body mass in Mandrillus leucophaeus | journal=Primates | volume=47 | issue=2 | pages=151 | doi=10.1007/s10329-005-0164-6] [cite journal | author=Joff et al. | year=2005 | title=Fetal and infant head circumference sexual dimorphism in primates | journal = Am J Phys Anthropol | volume = 126 | issue = 1 | pages = 97–110 | doi=10.1002/ajpa.20035] This area is currently being investigated as sexual dimorphism is one of the major potential sources of variation that must be taken into account when assessing the number of species represented in a fossil sample and the second is that there have been some strong links between sexual dimorphism and ecological variables in extant species. Thus, by establishing the nature of sexual dimorphism in fossil species it has been possible to make conclusions about their social systems and habitat preferences.

exual dimorphism in primate teeth

Primates, such as baboons, are well known for their highly sexually dimorphic canine teeth, with males possessing canines that are up to 4 times taller than those of females. [cite journal | author=Plavcan, J. M., & Ruff, C. B. | year=2008 | title=Canine size, shape, and bending strength in primates and carnivores | journal = Am J Phys Anthropol | volume = 136 | issue = 1 | pages = 65–84 | doi=10.1002/ajpa.20779] Primate canine dimorphism has been extensively documented, with the consensus that large male primate canines serve as weapons for intrasexual competition, and some evidence that large female canines also have this function. Primate canine teeth are as large or larger as similarly sized carnivores; they also seem to have been selected for their strength and length does not necessarily impact on canine function.fact|date=May 2008 In deciduous teeth it has been shown that Cercopithecidae, with the exception of "Papio cynocephalus", showed no significant sexual size dimorphism and that it would be problematic to use deciduous teeth in species determination. [cite journal | author=Koppe, T. and Swindler, D. R. | year=2004 | title=Metric sexual dimorphism in the deciduous teeth of Old World monkeys | journal = Annals of Anatomy | volume = 186 | issue = 4 | pages = 367–374 | doi=10.1016/S0940-9602(04)80065-7] Phylogenetic comparative methods have been used to analyze the consequences of sexual selection on canine size and canine size dimorphism in primates. The analyses indicated that in Haplorrhini the degree of sexual selection is correlated with canine size dimorphism, as well as with canine size in both sexes. Matched-pairs analyses on canine size after correcting for the effects of body size showed significant effects of sexual selection on relative canine size, indicating that canine size is more important in haplorrhine male-male competition than body size.

ee also

*Sex differences in humans

References