抄録
Perineal sexual swelling in relation to menstrual cycle occurs in a variety of primate taxa. However, sexual swelling with exaggerated size and color is found only in some Old World monkeys and two Pan species. Although several hypotheses have been proposed (e.g. reliable indicator hypothesis and graded signal hypothesis), it seems unlikely that a single hypothesis can account for the significance of the sexual swelling in all Old world monkeys and Pan species. Bonobos (Pan paniscus) provide an excellent opportunity for studying sexual swelling since they have the most prolonged maximal swelling periods among primates. Although many studies has examined the roles of sexual swelling in the context of male-female relationships, in this study we established and tested a new hypothesis that sexual swelling of female bonobos increases their attractiveness to other females and thereby facilitates social interaction between females. We found that female bonobos with maximal sexual swelling engaged in social interactions with other females, (e.g. g-g rubbing, staying in close proximity and grooming) more often than females without maximal swelling, which suggested that females with maximal swelling were attractive to other females for a.liative interactions. The results also suggested that the benefits of maximal swelling may vary among females depending on their age which reflect their life-history stages. In particular, young females may get more benefits from prolonged maximal swelling through increased grooming reciprocation and staying in close proximity to other females.
