It has already been shown that there is a distinct relationship between the diet of a primate, and its body size. This relationship has to do with the type of food eaten, its nutritional value, and the metabolism of the primate in question. For example, insects, a good source of protein and calories, may be able to provide all the dietary needs of a small animal, but may not be enough to meet the energy needs of a larger animal with a slower metabolic rate. However do body size and diet have anything to do with a primates’ mating behavior? Moreover, does it affect female choice? Does a male’s body size may make him more attractive to a prospective female mate, and does the type of food eaten also affect when a female wants to mate with a particular male? It seems that they do, “…the selection of particular food items may play a more critical role in reproduction and health than we have assumed previously” (Coichon and Nisbett, p. 133).

First of all, body size increases through evolutionary time with folivory (Ciochon and Nisbett, p.134). A large body size and a slow metabolism usually go hand in hand with each other. At Kay’s Threshold, of 500 g, an animal must increase its intake of both calories and proteins in proportion with how much energy it uses to acquire its food, in order to get a balanced diet. Therefore, if the food source that is most readily abundant is leaves and fruit, then it can be assumed that large slow metabolismed primates can be found feeding on them. And if a small primate is found, it can be inferred that the diet of that primate is mainly insects. Basically, the upper size limit of an insectivore is only limited by the energy exerted to hunt prey, and only its metabolism and digestive system determine the lower size limit of a folivore (Ciochon and Nisbett, p. 134)

It has been shown also that diet can influence mating behavior. In the case of brown capuchin monkeys, it has been shown that female choice is very much influenced by diet (Janson, 1998). In brown capuchins, a dominant male is in control of which monkeys get to feed. This dominant male will let his offspring eat before any other monkeys in the group, “…males generally let their own offspring to feed beside them, and monkeys that fed near the highest-ranking male had higher feeding rates” (Boyd and Silk, p. 251). This is a very desirable thing have happen to their children for brown capuchin mothers. Therefore, the dominant male is very sought after by females in estrous. Females will choose him before any other male, and they will actively pursue him until he wants to mate (Janson, 1998). This behavior is based on the fact that brown capuchins are mainly frugivores, a resource that is patchy. Since these foods occur in patches that can be defended, the dominant male can use his influence to regulate who gets to eat. If these monkeys ate a different type of food, leaves for instance, as their many food source, then the dominant male could not determine which monkeys get to eat, and he would not be as actively pursued by female monkeys.

Body size, too, may influence female choice in some species of primates. It can be assumed that the larger a male is, the more successful he has been at finding food. This, in and of itself, is a very desirable trait to look for in a mate. In theory, a female will associate how large a particular male is with the fact that he can gather food well, and she will mate with him because she wants her offspring to have that trait as well. This, however, is not the only reason why a female would choose a mate who is large, there is also another reason: larger males can offer more protection for their group and their offspring. Among squirrel monkeys, males even take on excess water to inflate their body size and become more attractive to females during the breeding season (Boinski, 1998). Although the added size doesn’t directly make these males more able to defend their babies, it has been found that most enlarged males are more vigilant for predators, and are much more likely to directly intervene when babies or group members are threatened. This trait, symbolized by an enlarged body size, is very attractive to a female squirrel monkey.

There is a very well documented connection between body size and diet. They very definitely affect one another. It also seems that body size and diet also affect the mating system and the amount of female choice present in a primate society. It seems that the type of food a primate species prefers to eat can influence the social structure of the group and the reproductive success of some of the members of that group. Apparently, those males that have control of a food resource are more likely to the object of female choice. However, if the species prefers a food that does not occur in a manner where it can be dominated by an individual or small group of individuals, there is no difference between dominant males and other males, so the dominant male will not be the object of female choice. Also, it seems that in some species, the body size of a male serves as an advertisement to females of how successful he is at food gathering or protection of the group. These traits are highly desirable, and the female will make a male possessing these traits the object of her affections. Body size is directly related to diet, and apparently, female choice is directly related to both of them.
 
 
 
 
 
 
 

Bibliography
 

Boyd, Robert and Silk, Joan B., 1997, How Humans Evolved, W. W.                                                                          Norton, New York N. Y.
Ciochon, Russell L. and Nisbett, Richard A., 1998, The Primate Anthology, Prentice-Hall, Inc., Upper Saddle River, N. J.
Janson, Charles H., 1998, Capuchin Counterpoint, In A Primate Anthology, 22:153-160
Boinski, Sue, 1998,  Monkeys With Inflated Sex Appeal, In A Primate Anthology, 25:174-179