Abstract

Females of some primates, exhibit exaggerated swellings of the perineal skin, particularly around the middle of the ovarian cycle. It seems inevitable that swellings are very costly for the females. However, sexual swellings have evolved independently at least three times in primates, suggesting a very strong selective advantage. Although there is consensus that sexual swellings have evolved in the context of sexual selection, their functional significance remains unsolved. The present study (at Kibale National Park, Uganda) is the first detailed study on mating strategies in Procolobus tephrosceles. The aim is to investigate how accurate sexual swellings are as indicators of female receptivity and how female behaviour and receptivity differs in P. tephrosceles and P. badius. Sexual swellings in P. tephrosceles are a lot smaller than those in P. badius. We showed that, in contrast to P. badius, female P. tephrosceles don’t emit copulation calls. Possibly, female P. tephrosceles have more control over mating partners than P. badius due to a lower degree of male aggressiveness and less reproductive overlap among females. In addition, females can be receptive for a month (or more) in both species and pregnant females develop swellings too. Our first analyses suggest that, although males are interested in both, they prefer females with conception cycles over those with post-conception swellings. Our preliminary results support the hypothesis that swellings evolved as a female counter-strategy to male coercion/monopolisation that maximises paternity confusion and female promiscuity.