The Reproductive Cycle of the Ring-Tailed Lemur (Lemur catta): Sex Steroid Levels and Sexual Receptivity Under Controlled Photoperiods

Abstract

During a photoperiodically regulated breeding season, the relation between sexual receptivity, gonadal hormones, and vaginal cornification was examined in 6 parous ring-tailed lemurs (Lemur catta) throughout the course of 9 ovarian cycles. We monitored estrous cycles by daily vaginal smears, and the duration of receptivity was determined by repeated pair tests (15 min) with one or more stud males, which were separated from the female before ejaculation. Concentrations of estradiol-17β (E2) and progesterone (P) were determined by radioimmunoassay. Mean (±SEM) peak concentrations of E2 (120 ± 30 pg/ml) were observed on the first day of fully cornified vaginal smears, i.e., during vaginal estrus. Receptivity occurred 26.33 ± 6.75 h after the E2 peak and persisted for 21.66 ± 5.76 h. Some females showed partner preference during the receptive period. Progesterone concentrations, which were low (3.3 ± 2.4 ng/ml) on the day of the E2 peak, rose gradually to peak values (92.5 ± 15.5 ng/ml) about 26 days later. At the onset of the breeding season and during a brief period of photically-induced quiescence within the experimental breeding season, P values remained low before the E2 peaks and the ensuing periods of sexual receptivity. Four females sampled on their first receptive pair test had plasma concentrations of P (1.4 ± 1.1 ng/ml) that were lower than luteal-phase concentrations (79.9 ± 11.6 ng/ml). These data demonstrate a correlation between sexual receptivity, vaginal cornification, and periovulatory gonadal hormone changes in L. catta and suggest that estrogen alone activates receptivity in this species. The regulation of receptivity in L. catta resembled the regulatory mechanisms of rodents in the restriction of receptivity to the periovulatory period. However, the failure of some L. catta pairs to copulate during the female's period of receptivity demonstrates that partner preference is also a factor.

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