Reproductive behavior in P. cynocephalus is closely tied to social organization. Because these animals live in multi-male, multi-female troops, there is the potential for any male to mate with any female. Males therefore compete fiercely for access to sexually receptive females. In general, a male’s ability to consort with a female and exclude other males from access to her is related to the male’s ability to compete with other males. There is therefore a correlation between male dominance rank within the troop and mating success. Larger, younger, and stronger males have a distinct advantage in this type of competition.
It should be noted that as in many other social animals, there can be other factors which affect a male’s mating success. For example, males may form alliances with other males, subverting the normal dominance hierarchy. Two males, neither of whom can dominate a third male alone, may join forces. As a coalition, these males may succeed in securing access to a sexually receptive female. Such coalitions are reciprocal, and typically occur between pairs of older males who are well acquainted with one another through mutual tenure in a troop.
Males also follow a strategy of developing "friendships" with females This enhances their opportunities to mate. In these friendships, males groom, share food, and have strong affiliative ties with particular females and their offspring. It is common for males to defend their female friends during agonistic encounters with other females, and with other males. These associations are not confined to the period during which females are sexually receptive, but span the entire gamut of the female’s reproductive life—including pregnancy, lactation, and time spent cycling. Females exhibit a preference for mating with their male friends, and therefore make consortships with their male friends more likely. In addition, because females prefer their friends as mates, they are more likely to cooperate with them in the maintenance of a consortship than they are to cooperate with other, less favored, males.
In P. cynocephalus, females mate with a variety of males during any given estrus cycle. Such multiple matings are not necessary to ensure fertilization, and may function to confuse the actual paternity of the female’s offspring. This may help to mitigate infanticidal tendencies of males.
Mating System: polygynandrous (promiscuous)
Reproduction in P. cynocephalus is related to the social structure of this species. Yellow baboons live in multi-male, multi-female troops. Mating is polygynandrous, with both males and females mating with multiple partners. Most matings occur during consortships. Consortships arise when a male, through aggression toward potential rivals, is able to maintain exclusive sexual access to a female. Females may consort with multiple males while they are sexually receptive, although they consort with only one male at a time. Because it is apparently easier for a male to maintain exclusive access to a female if the female is cooperative, there is a significant amount of female mate choice, with females preferring some partners over others.
Females characteristically have an estrous cycle of 32 days in length, however, cycle length varies between individuals and between populations. At the Tana River National Primate Reserve in Kenya, primiparous females had the longest cycles, averaging 44 days, and multiparous females had the shortest cycles, averaging 37 days. These cycles are much longer than the 32 to 34 day cycles reported in Amboseli National Park. Differences may be related to nutritional differences between populations, social differences, or they may reflect underlying genetic differences.
There is a noticeable menstrual flow for approximately three days per cycle if the female does not conceive. During the period around ovulation, the perineal skin of the female swells, alerting the males to her potentially fertile condition, and enhancing her attractiveness to them. Mating is initiated by the female, who presents her hindquarters to the male. When females are cycling, mating frequency can be from 1 to 6 times per hour. When females become pregnant, they cease to mate at all. Their pericallosal skin turns red as a result of increased blood flow to the region, alerting other members of the group to their reproductive condition.
Gestation lasts about 175 to 181 days, after which the female gives birth to a single offspring, weighing approximately 854 g. This is significantly smaller than the 1068 g neonates reported for P. anubis. The neonate has a black or reddish coat, depending upon the subspecies. This makes it easy to distinguish neonates from older infants. An infant is completely dependent upon its mother for the first few months, until it begins to eat solid food and is able to walk on its own. Age at independence is difficult to estimate, because even if the mother dies, a young baboon may continue to receive care from adult males, or other female kin. Independence is often listed as the age of weaning.
Females have an interbirth interval of approximately 21 to 27 months. This interval varies geographically, as well as according to maternal age and maternal rank. Interbirth intervals were longer at Tana River than at Amboseli, perhaps in part because the probability of infant survival to 24 months of age was greater. However, in anubis baboons, it has been shown that females who are older or have a higher rank tend to have shorter interbirth intervals, probably because these females experience enhanced nutritional status and are free from harassment by higher ranking females. The interbirth interval is also shorter if an infant dies before weaning.
Weaning occurs sometime around 1 year of age. Lactation is a huge cost for adult females, and has been shown to cause a reduction in female weight. Lower ranking and younger females probably take longer to recover adequate body weight to reproduce than do older, dominant females, explaining their longer interbirth intervals.
The onset of puberty and attainment of adult size is highly variable and is associated with nutrition levels in closely related anubis baboons. The effect of nutrition on growth is so strong that as little as 15 to 16 weeks of dietary variation in newborns can have lasting effects on overall rates of female growth, absolute adult weight, and age at menarche. This may be one reason that differences have been noted in the age of menarche in geographically separated populations.
In yellow baboons, puberty occurs between the ages of 5 and 6 years in females, and is signaled by menarche, or in some cases, first pregnancy. In males, there is greater variation in age at onset of puberty, with sexual maturation occurring between the ages of 4 and 7 years. Between 70 and 97 per cent of males emigrate from their natal troop sometime before reaching sexual maturity. Although females typically spend their entire lives in their natal troops, some transfer of females to new groups has been observed.
Breeding interval: Female yellow baboons may breed annually under some conditions, but are more likely to reproduce every other year.
Breeding season: Mating and births may occur throughout the year.
Average number of offspring: 1.
Range gestation period: 175 to 181 days.
Average weaning age: 12 months.
Range time to independence: 12 to 18 months.
Range age at sexual or reproductive maturity (female): 5 to 6 years.
Range age at sexual or reproductive maturity (male): 4 to 7 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous
Most parental behavior is performed by the female. Females nurse, groom, and play with their offspring. Females express different patterns of infant care, often associated with rank and age. In yellow baboons, higher-ranking females tend to be more "permissive" in their parenting than lower ranking females, who tend to be more nervous and "restrictive," preventing their offspring from moving away from them. Such differences may be related to the amount of harassment females of lower rank are likely to receive. Another difference seen in maternal behavior in this species is that older mothers are known to spend more time in contact or close to their infants and are less likely to terminate bouts of nursing than are younger females. First-time mothers are also likely to reject infants sooner than are experienced mothers. These differences may affect interbirth intervals.
Cooperative care of offspring is not present in P. cynocephalus, but it is not uncommon for females other than the mother to groom an infant, sometimes providing allomaternal care to the infant. Subadult and juvenile females who have not yet reproduced themselves are most likely to exhibit allomaternal behavior. Other factors known to affect the incidence of allomaternal behavior in most cercopithecine species include the infant’s age, and relatedness of the allomother to the mother and infant. As is the case for all baboons, infants are very attractive to other members of the social group, and are the focus of a great deal of investigation and attention, especially while they are still displaying their black natal coats. In extreme cases, females may kidnap the offspring of other females. Lower-ranking females have been reported to be subjected to this extreme form of harassment more often than have higher-ranking females. However, in an analysis of infant handling, Bentley-Condit et al. (2001) found no consistent association between mother’s rank and how often her infant was handled. Although females attempted to handle infants of females of like rank or lower more often than they attempted to handle the offspring of higher ranking females, mothers were able to successfully rebuff more than three quarters of all handling attempts.
Males have complex relationships with infants and juveniles, which in some cases may be a form of parental care. Males are known to carry, protect, share food (especially meat), groom, and play with, the offspring of their female friends. Because they are more likely to mate with their female friends than they are with other females, these infants and juveniles are more likely to be their own offspring than are other immature animals within the troop. This behavior, therefore, can be interpreted as paternal.
However, it should be noted that the relationship between adult males and these immature animals may be more complex than this. There may be some form of reciprocity involved. Adult males will often carry infants during tense interactions with other adult males. This carrying can be initiated either by the adult male or by the infant. Such contact with an infant during agonistic encounters may have the effect of inhibiting aggression by other males. The favors bestowed upon an infant used as a buffer may therefore be a form a "payback" from the adult male. However, since the tendency to use an infant as an agonistic buffer is related to familiarity with the infant and the probability of paternity, it is impossible to separate the nepotism from the reciprocity of such interactions.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning; inherits maternal/paternal territory; maternal position in the dominance hierarchy affects status of young
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