Female Sexual Swellings in the Asian Colobine Simias concolor.

During a preliminary study of pig-tailed langurs (Simiacs concolor) in the Pagai Islands, Indonesia, it was discovered that females exhibited conspicuous swelling of the urogenital triangle. The pig-tailed langur is the first Asiatic colobine found to have prominent sexual swellings and the only colobine with sexual swellings that lives in one-male groups. Because all anthropoids with conspicuous sex skin typically live in groups having female-biased adult sex ratios, it is possible that females might compete amongst themselves for the male in one-male groups, or the best males in multimale groups. Sexual swellings may therefore have resulted from sexual selection for signals attractive to makes in female-female competition, as suggested earlier by Bercovitch (California Anthropologist 8:9-12, 1978). Prolonged observation of recognizable individuals will be required to test this hypothesis in the pig-tailed langur and other species. [ABSTRACT FROM AUTHOR]