Ecological conditions, feeding and ranging behaviour as well as physical condition of female Hanuman langurs (Presbytis entellus) were studied in order to analyse the major influences on the timing of reproductive events. The langurs inhabited a semi-evergreen forest dominated by Sal trees (Skorea robusta). The climate was dominated by the summer monsoon lasting from May to September. Availability of plant phytophases was markedly seasonal, with fruiting as well as flushing of the six main food plants during the monsoon. Feeding and ranging behaviour of the females varied with food availability and its distribution. High dietary quality was only obtained during a short period from May to July. Physical condition of the females varied in accordance with dietary quality and energy expenditure, with a good physical condition during the second half of the year. Births occurred from January until June, with most births around the energetically worst period of the year. The results indicate that, in contrast to several other non-human primates, most females of this population gave birth too early to meet the optimum lactation requirements. Complete weaning mainly took place during an energetically bad time of the year (October to December). However, it can be inferred that the reduction of suckling bouts prior to the next conception took place when high quality food was available. Conceptions were confined to the months of July to November, coinciding with the time of best physical condition. Moreover, females who conceived were in a better physical condition than those who failed to conceive, suggesting a primary influence of nutrition on the probability of conception. Seasonality and timing of births may be the result of a regular seasonal shortfall of resources influencing the ability of the females to ovulate and to conceive.

Ecology, nutrition, and timing of reproductive events in an Asian primate, the Hanuman langur (Presbytis entellus)

Seasonally recurring patterns in physiology and behavior are pervasive in nature. These often reflect adaptive, anticipatory responses to annual energetic constraints. This chapter reviews biological timekeeping mechanisms that allow mammals to engage seasonal phenotypic transitions. The overwhelming majority of research into mammalian seasonality has focused on the reproductive system. This chapter not only emphasizes lessons learned from the study of seasonal reproduction, but also considers mechanisms of seasonal changes in aggression, immune function, and cognition. In a species- and trait-specific manner, the exegesis of seasonality invokes measurement of day length (photoperiodism), the induction of photorefractoriness, and the activity of endogenous self-sustained circannual oscillators. Formal models of seasonal timekeeping are elaborated, and the phenomenology of seasonality in rodents and primates is reviewed. Evidence toward the critical nature of photoperiodic changes in nocturnal melatonin production is presented, the neural substrates that participate in responsiveness to melatonin, and the neuroendocrine events occurring downstream of melatonin signaling are also reviewed.

Mammalian Seasonal Rhythms: Behavior and Neuroendocrine Substrates

To date, it is not known whether the seasonal occurrence of sexual behavior and mating in free-ranging Hanuman langurs at Ramnagar, Nepal, is correlated with seasonal changes in female ovarian function, and, if so, which factor(s) triggers the onset of the reproductive period. Using non-invasive fecal hormone analysis in combination with behavioral observations, this study was carried out to: 1) investigate and characterize seasonal patterns of ovarian cyclicity and timing of conception in wild langur females living in a highly seasonal habitat; and 2) examine the relationship between seasonal patterns of ovarian cyclicity, behavioral estrus, and female physical condition. Behavioral data and fecal samples were collected during a total period of 14 months from nine females living in a multi-male group. Physical condition of the females was assessed monthly by visual inspection, using a seven-fold scale. Ovulatory cycles and timing of conceptions were identified by the measurement of immunoreactive pregnanediol glucuronide (iPdG) in extracted feces. Hormone profiles in individual females revealed a clearly seasonal distribution in the occurrence of ovulatory cycles, which were restricted to the period from July to October. The distribution of female estrus behavior showed a similar seasonal pattern, and in total 88.2% of all estrus periods observed in the focal females were accompanied by ovulation. Onset of ovarian cycles as well as mating activities were strongly correlated with the onset of the rainy season. Females conceived, on average, in their second ovulatory cycle (pregnancy length: 211.6 ± 3.4 days), with timing of conception being confined to the months when animals showed an improved physical condition. Collectively the present data clearly suggest that in seasonally-breeding langurs at Ramnagar, ecological conditions (rainfall, food availability, and quality) influence the onset of ovulations and timing of conceptions. Am. J. Primatol. 51:119–134, 2000. © 2000 Wiley-Liss, Inc.

Hormonal correlates of reproductive seasonality in wild female hanuman langurs (Presbytis entellus).

In sexually promiscuous mammals, female reproductive effort is mainly expressed through gestation, lactation, and maternal care, whereas male reproductive effort is mainly manifested as mating effort. In this study, we investigated whether reproduction has significant survival costs for a seasonally breeding, sexually promiscuous species, the rhesus macaque, and whether these costs occur at different times of the year for females and males, namely in the birth and the mating season, respectively. The study was conducted with the rhesus macaque population on Cayo Santiago, Puerto Rico. Data on 7,402 births and 922 deaths over a 45-year period were analyzed. Births were concentrated between November and April, while conceptions occurred between May and October. As predicted, female mortality probability peaked in the birth season whereas male mortality probability peaked in the mating season. Furthermore, as the onset of the birth season gradually shifted over the years in relation to climatic changes, there was a concomitant shift in the seasonal peaks of male and female mortality. Taken together, our findings provide the first evidence of sex differences in the survival costs of reproduction in nonhuman primates and suggest that reproduction has significant fitness costs even in environments with abundant food and absence of predation.

/pdf/sex-differences-in-survival-costs-of-reproduction-in-a-511rbvfzzk.pdf

Sex differences in survival costs of reproduction in a promiscuous primate

SYNOPSIS. Social groups of rhesus monkeys ( Macaca mulatto ) living in outdoor environments exhibit a distinct seasonal mating pattern and female rhesus are observed to be sexually receptive for discrete periods averaging about 9 days duration. In the laboratory environment mating occurs throughout the year and, in the pair test, female rhesus are observedto be sexually receptive through all phases of a menstrual cycle, with a periovulatory peak incopulatory behavior. The apparent conflict between results from field and laboratory studies has been difficult to resolve because of methodological limitations inherent in each study environment. Studies conducted on social groups of rhesus monkeys housed in outdoor compounds, an environment in which the species typical seasonal mating pattern is preserved and which allowsfor concomitant measurement of behavioral and hormonal variables, provided information about the covariance between female sexual behavior and ovarian cycles. Female copulations were observed only in association with ovulatory cycles, and were limited to the follicular and peri-ovulatory phases of such cycles, demonstrating that copulatory behavior in female rhesus monkeys is strongly influenced by cyclic hormonal variables. The studies also revealed that females tend to conceive on the first ovulatory cycle of the season, that there was no synchrony of cycles among the females, and that the best predictor of the timing of ovulation in a particular female is reproductive outcome in the previous year.

Reproductive Behavior in the Rhesus Monkey: Social and Endocrine Variables

An experiment was designed to examine the effect of season on frequency of ovulation and to estimate the proportion of ovulatory cycles during the summer and winter months in feral rhesus monkeys housed under conditions of controlled light and temperature. The frequency of ovulatory menstrual cycles was determined for 9 monkeys in the summer months of June July and August and again during December January and February. Occurrence of ovulation was determined by observations of the ovary at laparotomy. 5 of 24 menstrual cycles during the summer and 30 of 31 cycles during winter were ovulatory. The 5 ovulatory summer cycles were distributed among only 2 of the animals; the other 7 animals did not ovulate during the summer. The proportion of monkeys which ovulated during the summer months was 22%. Summer menstrual cycles showed greater variability in length than those occurring during the winter. The data suggest that some monkeys maintain a seasonal anovulatory season even in the absence of seasonal light and temperature variations. Other monkeys do ovulate during the summer presenting the possibility of selecting these animals for breeding colonies.(Authors modified)

/pdf/the-effect-of-season-on-occurrence-of-ovulation-in-the-4eynbucb11.pdf

The Effect of Season on Occurrence of Ovulation in the Rhesus Monkey

Blood samples were obtained from both ovarian veins in 5 rhesus monkeys during the luteal phase of the menstrual cycle. Mean progesterone concentrations in both veins were significantly greater than peripheral blood levels [407 ng/ml plasma in the vein on the side of the corpus luteum (CL), 83 ng/ml plasma in the ovarian vein on the side without the CL, and <7 ng/ml in peripheral plasma]. A hemostat was placed between the ovary containing the CL and the uterus to prevent blood flow between them, and another blood sample was obtained on the side without the CL. After preventing blood flow in this manner, the progesterone concentration in the vein on the side without the CL was lowered (p <0.05) to nearly that of peripheral blood, suggesting the presence of vascular channels which permit blood from one ovarian vein to flow to the other side via the uterine circulation prior to entering the general circulation. (Endocrinology 86: 1212, 1970)

Origin of ovarian venous progesterone in the rhesus monkey.

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The Effect of Season on Occurrence of Ovulation in the Rhesus Monkey

Origin of ovarian venous progesterone in the rhesus monkey.