Paul Winkler

Males as infant protectors in Hanuman langurs (Presbytis entellus) living in multimale groups – defence pattern, paternity and sexual behaviour

Abstract Hypotheses about the evolution of gregariousness and social organisation in primates are based on ecological explanations as well as on social factors such as conspecific threat (especially infanticide by males). The social explanation fits well with the conditions found in strepsirrhine primates and furthermore explains why infanticide in anthropoid primates living in one-male groups mainly occurs when the resident male (protector) is replaced. However, whether it likewise fits to the conditions in multimale groups will depend on the role of resident males as infant protectors, which has rarely been examined. We investigated long-term data of wild Hanuman langurs (Presbytis entellus) inhabiting a forest near the village of Ramnagar (southern Nepal). Twenty-two eye-witnessed attacks on infants by males were analysed in connection with male residency, paternity (DNA analyses) and sexual behaviour. Adult males played a major role in infant defence (65%). Only the genetic father or males who had been residents when the infant was conceived were observed to protect infants. Males who immigrated after a female had conceived may later attack her infant and were never observed to defend it. lt seems that the males took only copulations with potentially fertile females but not with pregnant females as clues for paternity. In the light of these results it seems likely that the risk of infanticide is an important determinant in female-male associations even in anthropoid primate multimale groups.

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

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.

DNA analyses support the hypothesis that infanticide is adaptive in langur monkeys

Although the killing of dependent infants by adult males is a widespread phenomenon among primates, its causes and consequences still remain hotly debated. According to the sexual selection hypothesis, infanticidal males will gain a reproductive advantage provided that only unrelated infants are killed and that the males increase their chances of siring the next infants. Alternatively, the social pathology hypothesis interprets infanticide as a result of crowded living conditions and, thus, as not providing any advantage. Based on DNA analyses of wild Hanuman langurs (Presbytis entellus) we present the first evidence that male attackers were not related to their infant victims. Furthermore, in all cases the presumed killers were the likely fathers of the subsequent infants. Our data, therefore, strongly support the sexual selection hypothesis interpreting infanticide as an evolved, adaptive male reproductive tactic.

Paternity analysis of alternative male reproductive routes among the langurs (Semnopithecus entellus) of Ramnagar.

Because primate males usually invest very little in offspring, male reproductive success will mainly be determined by access to fertile females with differences in access leading to differential male reproductive success. To determine the outcome of alternative male reproductive routes, we investigated a wild population of Hanuman langurs at Ramnagar, South Nepal, where groups were either one-male or multimale. Paternity was established by DNA analysis from faeces for 42 infants in five groups. In one-male groups all infants were sired by the only resident male in the group. In multimale groups the alpha male fathered significantly more infants (57%) than all other resident males. Nonresident males sired at least 21% of all infants born into multimale groups. Because of the lower mean number of infants sired by alpha males during their whole tenure as alpha compared with males in one-male groups (2.3 versus 6.8) and the higher maximum value (8.9 versus 6.0), the alpha male route is considered the riskier option. Based on demographic data we suggest that the considerable variance in short-term reproductive success might not translate to the same degree into differences in long-term reproductive success. Copyright 2001 The Association for the Study of Animal Behaviour.

Life history of Hanuman langurs (Presbytis entellus). Reproductive parameters, infant mortality, and troop development.

Longitudinal data of reproductive parameters from two langur troops (Presbytis entellus) at Jodhpur, Rajasthan, India, are presented. Females can reach menarche at approximately 29 months of age and conceive about 5 months later. Gestation length is about 200 days, average cycling length is 24 days, and mean interbirth interval 15.3 months. Postpartum amenorrhea, which ranges from 80-140 days will be reduced to 23-80 days in cases of stillbirths or early losses of infants, a fact that bears consequences in regard to the discussion of infanticide and reproductive advantage. Troop development showed distinct differences in two neighboring troops, especially in number of surviving female infants until sexual maturity. Both troops taken together, 77.9% of the newborns reached the infant-II stage (6 months), 59.3% survived until their mothers next infant (average, calculated for the mean birth interval of 15.3 months), and only 35.9% completed the 2nd year of life.

The Adaptive Capacities of the Hanuman Langur and the Categorizing of Diet

The diet of primates and related features are of great interest to primatologists from various disciplines. Although there are considerable differences between ethologists, functional morphologists, physiologists or nutritionists, there is the unique tendency to classify various types of diets as well as the single primate species according to its diet. Thus, labels such as frugivorous, folivorous, insectivorous are used, and the consequences for primates of different categories are discussed in relation to evolutionary trends, habitat, behaviour, and so forth.

Twins in free-ranging Hanuman langurs (Presbytis entellus)

Two pairs of twins were observed in free-ranging Hanuman langurs (Presbytis entellus) at Jodhpur, India. Each twin had a preferred nipple for suckling, the preference of which developed during the first 5 weeks of life. The behaviour of the twins was mostly synchronized. In more than 60% of all activity bouts both showed the same behaviour, with “nipple contact” and “playing” prevailing. Differences in physical strength and development were apparent within each pair. While the total amount of allomothering was almost the same, individual weekly scores differed considerably.