Reproductive behavior in P. ursinus is closely tied to social organization. When these animals live in multi-male, multi-female troops, there is the potential for any male to mate with any female. Because of this, males in multi-male troops 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.
However, as in many social animals, there are other factors which affect a male’s mating success. For example, in P. anubis males may form alliances with other males, which can subvert the normal dominance hierarchy. Two males, neither of whom can dominate a third male alone, may join forces and together, as a coalition, these males may succeed in securing access to a sexually receptive female. Such coalitions may occur in chacma baboons, although research has yet to address this behavior in P. ursinus.
In anubis baboons, males also follow a strategy of developing "friendships" with females, which 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 tend to 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. These types of long-term friendships may also exist in chacma baboons, although further research is needed to clarify this point.
Females clearly exert some mate choice. In addition to having sexually proceptive behavior, in which the female makes some decision about which males she will mate with by presenting her hindquarters to those males, they may refuse to mate with some males. When new males immigrate into a troop, females may help or hinder their chances of success by developing affiliative relationships with the immigrating males. In this way, females may choose which males will be in their potential mating pool.
Mating System: polygynous ; polygynandrous (promiscuous)
Reproduction in P. ursinus is related to the social structure of this species. The social structure is somewhat variable, with the majority of animals living in multi-male, multi-female troops reminiscent of anubis baboons. In some cases, however, the social structure resembles that of hamadryas baboons, with single males controlling a group of females. Mating in multi-male, multi-female troops is polygynandrous, with both males and females mating with multiple partners. Mating in One Male Units (OMUs) is necessarily polygynous.
Most matings in multi-male, multi-female troops 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 during the periovulatory period, 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.
In OMUs, males do not alter their general behavior toward females, with the exception of mating with them mostly when the females are close to ovulation. Males in OMUs do not consort with females. If another adult male enters the group, however, this behavior changes drastically, with typical competition between males and consortships developing.
Females characteristically have an estrous cycle of 31 to 35 days in length. 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. Females are sexually receptive and mate throughout their cycle, but copulations peak at midcycle when the female is likely to ovulate. Mating is initiated by the female, who presents her hindquarters to the male. Like hamadryas baboons, chacma males are serial mounters. A male will mount a female several times, with 1 to 20 thrusts per mount, before ejaculating. When the female is cycling, mating frequency can be as high as 7 to 12.2 copulations per hour. Mating does not occur during pregnancy.
Gestation is probably similar to that of other Papio species, which ranges from 175 to 180 days. Females give birth to a single offspring. The newborn of P. anubis weighs 1068 g on average, and the young of chacma baboons are probably similar in size. The neonate has a black coat, making it easy to distinguish 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. Females have an interbirth interval ranging from 18 to 24 months. As in other baboons, it is likely that this interval varies according to a number of factors. In anubis baboons, females who are older or have a higher rank tend to have shorter interbirth intervals. Interbirth interval is also shorter if an infant dies before weaning.
Data on the nursing period in this species are scanty. However, it is likely that timing and patterns resemble other members of the genus. Weaning typically occurs in P. anubis around 420 days of age. Lactation is a huge cost for adult females, and has been implicated in dramatic weight reductions in anubis females. Lower ranking and younger females probably take longer to recover adequate body weight to reproduce than do older, dominant females, due to their reduced access to prime feeding sites. This would explain their longer interbirth intervals.
The onset of puberty and attainment of adult size are variable and are associated with nutrition levels. For example, in P. anubis populations where baboons are known to raid human crops, and to thereby secure greater access to nutrients than naturally foraging animals, puberty can occur much earlier. The effect of nutrition on growth in P. anubis 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. It is reasonable to assume that chacma baboons are similarly affected.
In P. ursinus females reach sexual maturity at approximately 3 years of age. Male sexual maturity occurs around 5 years of age. Within about a year, these animals will reach full size, or experience their first birth. There are no data available regarding the maturation of testicles or sperm production in this species. However, because chacma baboons have a variable mating system, and mating system differences have been implicated as the evolutionary cause of differences in the schedule of sexual maturation between anubis and hamadryas baboons, such data would be very interesting.
Breeding interval: These animals can breed every 1.5 to 2 years.
Breeding season: Mating can occur throughout the year.
Range number of offspring: 1 (low) .
Average number of offspring: 1.
Average time to independence: 12 months.
Average age at sexual or reproductive maturity (female): 3 years.
Average age at sexual or reproductive maturity (male): 5 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous
Most parental care 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 me more nervous and "restrictive," preventing their offspring from moving away from them.
There does not seem to be cooperative care of offspring among females in P. ursinus, but it is not uncommon for females other than the mother to groom an infant, sometimes providing allomaternal care to the infant. As in other baboons, subadult and juvenile females who have not yet reproduced themselves are most likely to exhibit allomaternal behavior. 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 coat. In extreme cases, female anubis baboons may kidnap the offspring of other females. Lower-ranking females are more often subject to this extreme form of harassment than are higher-ranking females. Other factors known to affect the incidence of allomaternal behavior in other species include the infant’s age, and relatedness of the allomother to the mother and infant.
Males have complex relationships with infants and juveniles, which in some cases may be a form of parental care. In other savanna baboon species, 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. Although not specifically reported for chacma baboons, it is likely that this behavior does occur in this species.
However, it should be noted that the relationship between adult males baboons and 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 in baboons and macaques familiarity with an infant is associated with 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: 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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