Biology, Eastern Michigan Universirty
Friday 8:30-8:45, Ballroom A
Squirrel monkeys (genus Saimiri) live in large social groups and are seasonal breeders. The unique reproductive physiology of males is suggestive of sexual selection. Males show weight gain during the mating season, which produces a "fatted" appearance in the upper arms and torso. Although much is known about the physiology of fatting, its evolutionary function remains unknown. Here I present data on wild Saimiri sciureus studied in Brazil, in order to describe male mating investment in the species, and to examine the hypothesis that male fatting is a product of sexual selection. Males were observed via focal animal sampling during four mating seasons. Male behaviors such as branch sniffing, genital sniffing and “draping” were observed. Compared to less robust males, fatter males spent significantly more time near females (F 2,72=5.62, p=0.005) and less time alone (F 2,72=4.27, p=0.01), and more time engaged in mating activities (F 2,63=3.95, p=0.02). The 2-month mating season accounted for 62% of all male–male agonism observed over 12 months. These results are suggestive of male-male competition for females. On the other hand, males did not coerce females to mate and females affiliated more with fatter males (F 2,18=11.2, p=0.005). These results are also suggestive of female choice. It is possible that male fatting in Saimiri is a product of both intra and intersexual selection. Continuing genetic analyses will address whether higher male fatting leads to increased paternity.
Funded by the National Science Foundation, American Philosophical Society, American Society of Primatologists, Animal Behavior Society, Sigma Xi and the University of Illinois.