Genital swellings in silvered langurs: what do they indicate?

Abstract

The occurrence of genital swellings was examined in adult female silvered langurs (Trachypithecus cristatus). In contrast to the exaggerated swellings found in cercopithecines and apes, genital swellings in silvered langurs are confined to the vulva and the surrounding perineum, but they may nevertheless convey information similar to that of exaggerated swellings (i.e., correlate with the receptive period and fertility). If so, genital swellings would be expected to occur most frequently in cycling females, and sexual behavior and male interest should most frequently involve females with swellings. Swellings during gestation, if they occur at all, should be most pronounced at the beginning. Swelling sizes (in three size categories) in nine adult females were examined throughout different reproductive states (cycling, pregnant, and lactating), and in relation to proceptivity, receptivity, and attractivity. Data were collected from November 2002 through March 2004 (on 500 of the 502 calendar days) at the Wildlife Conservation Society's Bronx Zoo. Female sexual behavior (proceptivity and receptivity) and male inspection (attractivity) were recorded each day for 6 hr by video camera (2,948 hr total) and analyzed as present or absent for each female day. Swellings were assessed directly (not from videotapes). In contrast to the predictions, swellings occurred significantly less frequently in cycling females (compared to pregnant females) and no regular, cyclic pattern could be detected. Some females conceived without a swelling. Female attractivity was independent of swellings but coincided with proceptive behavior. Swellings occurred most frequently in pregnant females, especially toward the end of the gestation period. Therefore, genital swellings in silvered langurs are not similar to exaggerated swellings or the smaller genital swellings that have been described for some other primates. It is currently not clear what they signal to conspecifics. Male behavior needs to be studied in more detail, and the hormonal basis for these swellings should be explored.

Mixed messages: wild female bonobos show high variability in the timing of ovulation in relation to sexual swelling patterns

“…At Luikotale, females’ MSPs generally increased in duration as time since parturition increased; however, the number of days since parturition did not have a statistically significant effect on MSP duration. Shorter MSPs following parturition could be caused by the energetic demands of lactation [ 124 ] and an associated decrease in ovarian steroid production [ 99 ]. However, some of our females had swelling cycles with prolonged MSPs while lactating.…”

Female reproductive parameters in the Javan gibbon (Hylobates moloch)

“…Sexual swelling was observed during gestation, which has also been observed in white-handed gibbons, but in both species the swellings do not follow a pattern [Barelli et al, 2007]. This has been noted in several primate species [silvered langurs (Trachypithecus cristatus): Shelmidine et al, 2007; Barbary macaques (Macaca sylvanus): Mo¨hle et al, 2005; chimpanzees (Pan troglodytes): Coe et al, 1979]. In most primates with gestational swellings, this occurs in the earlier stages of pregnancy.…”

Trachypithecus cristatus (Primates: Cercopithecidae)

“…Bernstein 1968;Borries and Koenig 2008;Furuya 1961;Wolf 1980). There are no external signs of estrus (vulval swellings occur minimally, not during the period of receptivity, and are not attractive to males- Shelmidine et al 2007). …”

“…Juveniles are 18-48 months old and subadults 36-48 months (Harvey et al 1987). Age at 1st birth ranges from 21.3 to 45.4 months and averages 34.6 months (Shelmidine et al 2007). T. cristatus have lived up to 31 years and 1 month in captivity (Nowak 1999).…”