can manifest itself in many different forms. In male and female primates there are obvious physical difference such as body size or canine size. Dimorphism can also be seen in skeletal features such as the shape of the pelvis or the robustness of the skeleton. There are two mating systems in the sexual selection of primates.
Intrasexual selection
Also known as male-male competition, intra-sexual selection occurs between males over a specific mate. This selection determines the reproductive success of the male by his athletic capabilities. The winning male in this combat will be rewarded in mating with the opposite sex primate. There is variation in the types of intra-sexual selection that occurs between primates. Dominant males are physically larger and stronger, which allows them to be fierce competition for females.
Verreaux's Sifaka
is a medium-sized primate of the Lemur family that resides in Madagascar. Living in groups, they are social creatures. This species is known for its casual mating style and vicious male-male competition. There are two basic forms of male to male competition in these primates:
Agonistic episodes
The male will bite, lunge, or attack an opponent during a brawl. These episodes are highly aggressive, ending in bloodshed.
Endurance episodes
Involved chasing and lunging between male primates. This will continue to go on until one of the parties collapses from exhaustion. The basis of this sexual selection relies on Verreaux's Sifaka's body and canine size. Sexual selection in this specific primate may favor a smaller, more agile male due to its ability to move quicker in the forest environment. Larger, more stocky males will be unable to move as quickly which gives the upper hand to smaller, more athletic males. Due to the survival of intermediate body size primates, this affects the evolution of the species type. Intermediate males mating with similarly sized females will not evolve the body size of these primates. This primate is just one example of the different forms of Intrasexual selection that is possible.
Intersexual selection
This form of sexual selection differs from intra-sexual selection as it focuses on the mutual participation from both sexes. This typically focuses on the female choosing the best mate rather than the male. This selection could include flashy colors, energetic displays of activity from the male species, valuable resources, or friendly behavior to the female. The individuals with these valued characteristics will have the best opportunity of finding a mate.
Mandrill
The mandrill can be found in tropical rain forest environments, usually in the thick bush but have also adapted to life on the ground. The sexual dimorphism in this animal focuses less on male-male competition but instead on physical attributes such as their body size and ornamentation. Their faces are brightly colored and stand out when looking for their female mate. When they find their mate, these primates typically remain involved in the offspring's life, offering grooming, protection, or entertainment to their offspring.
Academic Resources
The Differences between the sexes. Short, R. V., 1930-, Balaban, E., International Conference on Comparative Physiology. Cambridge: Cambridge University Press. 1994.. OCLC 28708379. Plavcan, J. Michael. "Sexual dimorphism in primate evolution". American Journal of Physical Anthropology. 116 : 25–53. doi:10.1002/ajpa.10011. ISSN 0002-9483. Larsen, C. S. “Equality for the Sexes in Human Evolution? Early Hominid Sexual Dimorphism and Implications for Mating Systems and Social Behavior.” Proceedings of the National Academy of Sciences, vol. 100, no. 16, 2003, pp. 9103–9104., doi:10.1073/pnas.1633678100. Leigh, Steven R. “Socioecology and the Ontogeny of Sexual Size Dimorphism in Anthropoid Primates.” American Journal of Physical Anthropology, vol. 97, no. 4, 1995, pp. 339–356., doi:10.1002/ajpa.1330970402. Scaglion, Richard. “On Australopithecine Sexual Dimorphism.” Current Anthropology, vol. 19, no. 1, 1978, pp. 153–154., doi:10.1086/202026. “Sexual Dimorphism.” The American Naturalist, vol. 37, no. 437, 1903, pp. 349–349., doi:10.1086/278295.
