Reproduction & Handrearing of Marmoset & Tamarins.
Marmosets and Tamarins have a rapid reproductive rate. They typically give birth to twins and there is no period of lactational anoestrus. A post-partum oestrus occurs within 10 days of parturition and conception rate at this oestrus is high. Some breeding females may be almost constantly pregnant. Gestation varies between Species. The lion tamarins have the shortest gestation at 128 days, while most other Species are reported to have a gestation of around 145 days. Cotton top tamarins have the longest known gestation at 183 days. Infant care is shared among group members. In most species other group members may participate in infant care by carrying the Infant from day l or 2. Contrary to earlier reports this is also true for lion tamarins. Goeldi's monkeys, on the other hand, are the exception to this with shared infant care not taking place until week three. In captivity the Callitrichidae are effectively monogamous. The dominant pair, who In most groups will be the parents of all other group members, suppress other adults within the group from breeding. This ensures that only the dominant pair breed, and generally means that inbreeding does not occur within groups. Rarely, however, incestuous matings and departures from monogamy occur. In the wild, a much more flexible reproductive strategy is apparent in most species for which good information is available
These points are discussed in more detail below.
The marmosets and tamarins are unique among simians in their habit of twinning. While single infants and triplets are not uncommon among marmosets and tamarins, the most frequent litter size is two. Occasionally, quadruplet births have occurred, but there are no reports of all four infants being born alive in Zoos or in the wild. The incidence of triplets has been reported to increase with time in captive colonies of and may relate to a high protein diet in captivity. It is unusual for all three infants of a triplet litter to be parent-reared in captivity. Recently, evidence from DNA studies has provided good evidence that triplets have been reared to independence in a wild group of jacchus. Callitrichid twins are dizygotic and share the same placenta and amniotic sac. Some considerable discussion has centred around whether twinning is a primitive feature that has been retained, or a derived feature, maintained that twinning was a primitive feature, while most other authorities have considered it derived, citing the highly specialised placentation, simplex uterus, and number of teats as evidence.
Care must be taken to distinguish between social group structure and mating relationships when discussing reproductive strategies. The presence in a group of more than one adult of either sex does not necessarily indicate that they are all reproductively active. They may, for instance, be non-reproductive mature offspring of the breeding male or female. In captivity, mature offspring may remain in a stable group and yet not enter a breeding relationship with their parents or siblings, as they are reproductively suppressed. The fact that a female may mate with more than one male is also not conclusive evidence of a polyandrous breeding system, although it is obviously suggestive of this. Only when paternity of offspring can be established will the breeding system be understood fully. In fact, in spite of the many reports of group structure indicating that there may be more than one breeding pair in a wild callitrichid group, only a few studies have actually reported seeing females mated by more than one male,even fewer studies have reported more than one breeding female in a social group at the same time. It is, however, not surprising that there is a paucity of data from wild groups. As pointed out, the marmosets and tamarins are small difficult to habituate to the presence of observers, and mating may last only a few seconds. Studies have shown. however, that even within a species the reproductive strategy may vary. Infant rearing is discussed more fully below.
Reproductive suppression of subordinate females among captive callitrichid groups is a well-documented phenomenon In C. jacchus. hormonal studies of females in peer groups have shown that the behaviourally dominant female is the only female to undergo normal ovulatory cycles. In nuclear family groups, it has also been shown that daughters do not exhibit ovulatory cycles and are therefore also suppressed in the three species some daughters do ovulate although they do not cycle regularly while still in their natal group and rarely this also occurs in S. oedipus. In Leontopithecus. on the other hand, daughters may undergo normal ovulatory cycles within their natal groups.Young females are often subject to severe aggression from their mother when they mature and are thus prevented from breeding through behavioural rather than physiological means. Physiological suppression of female cycles is by no means absolute. There are several instances of breakdown of suppression to suggest that something other than dominance is operating to maintain reproductive suppression of daughters within their natal groups and effectively acts as an inbreeding avoidance mechanism. Incestuous matings resulting in pregnancy do occur rarely in established breeding groups. If one of the parents of a group is removed it has been reported that in time suppression will eventually cease to be effective and incestuous breeding occurs. If a breeding male is removed, or dies, and replaced in a group with the surviving mother and her daughters, it should be expected that the male will breed with the daughters as well as the mother. While the group may remain stable for some time with more than one breeding female, it should be expected that eventually aggression between the females will occur resulting in the expulsion of one from the group.
Infant care patterns among the Callitrichidae
It has been suggested that twinning has major consequences for the breeding female among the Callitrichidae. Not only must the female carry twin foetuses through pregnancy, she must also rear them to independence. It has been showed that in captive cotton-top tamarins, energy intake by the female increased during lactation, and is showed in the same species that, when lactating, feeding rates of the female increased to a peak during the second month following birth, and only declined when infants began to receive food from other group members. Researchers have suggested that this is the reason for the communal or cooperative pattern of infant care seen among the callitrichids in which several, if not all, group members are involved in infant care and provision of food Recent reviewers of the social and reproductive systems of the marmosets and tamarins have attempted to interpret the inter-relationship between the sex ratio of wild groups, the mating systems that they exhibit and the role of helpers providing extra-maternal care of the offspring. These communal breeding systems have been referred to as 'cooperative polyandry'or 'functional polyandry. The variability shown both within and between callitrichid breeding systems is becoming increasingly apparent. For instance, differences have been highlighted between breeding systems of the marmosets and tamarins that probably relate to fundamental differerances in their ecology It is unlikely, therefore that such generalisations about the callitrichid breeding systems will be sustainable in the future.
Implications for captive management
Marmosets and tamarins breed within a tight cohesive social unit in captivity. For successful breeding stress needs to be minimised and groups should be maintained in their usual enclosure and with their usual group structure. It is vital, for instance, that breeding females are not separated from their groups prior to, or at parturition under normal circumstances. Mating is rarely seen, particularly within established groups of callitrichids. Mating occurs during pregnancy and outside the ovulatory period of the non-pregnant cycle, and hence conception dates are rarely known. As a rule of thumb, pregnancy is detectable visually about two months prior to parturition if it is possible to get a clear view of the abdomen of the breeding female prior to any feeding during the day. At one month prior to parturition abdominal swelling is usually clearly visible. Not all pregnancies can be detected visually and gaining reliable estimates of parturition dates is difficult based on female size, but this is nevertheless a useful indicator of when parturition may occur .Births almost invariably occur overnight. Many zoos put soft substrate of woodwool or similar material on the cage floor in preparation for parturition in case of falls. Occasionally births occur during the day, but this is usually an indication of a problem, although pied tarnarins have been often observed giving birth in the late afternoon rather than overnight. In some species there is a high rate of failure to rear young. In the event of infants being abandoned by the parents all possible attempts must be made to reintroduce them and induce parent rearing. If this fails, however, hand rearing may be attempted. Dead and mutilated infants are reported relatively frequently and may be due to several reasons. Stress at the time of parturition may induce infanticide and underlines the importance of reducing stress for these animals particularly at the perinatal period. Behaviourally incompetent parents may kill or injure infants. Overzealous grooming by a parent or sibling may result in injury to infants and should be monitored carefully. Landmarks in infant development are variable depending on many circumstances such as species, history of the family group (first time mothers are likely to show later landmarks than established breeding groups).Iinfants are carried for about two to three weeks, after which time they may, be seen taking tentative steps and mouthing food. By six weeks of age most are independent of the parents and weaning is well under way. By twelve weeks they are weaned and capable of independent existence. As reported in the section on social behaviour , infant care has a largely learnt component. It is vital that young are left with their natal group to experience and participate in infant rearing in order to become competent parents themselves.
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