Taxonomy and Conservation:
The Emperor Tamarin is a New World Monkey of the family Callitrichidae and is found in Central and South America. These primates are divided into six genera and the Emperor Tamarin belongs to the genus Saguinus. Saguinus is a large genus which includes 33 taxonomically distinct kinds of tamarins. The Emperor Tamarin or saguinus imperator is divided into two subspecies. These are the Black-chinned Emperor Tamarin or saguinus imperator imperator and the Bearded Emperor Tamarin or saguinus imperator subgrisescens.
The Emperor Tamarin is limited to the western Amazonian forest and live in the tropical rain forests of Peru, Brazil and Bolivia. They are considered endangered or threatened in some areas, while in other areas their status is classified as indeterminate. At the subspecies level, the black-chinned emperor tamarin is considered vulnerable while the bearded emperor tamarin is classified as “Least Concern” by the IUCN. However, in recent years, deforestation and destruction of their natural habitat is subjecting them to the danger of extinction.
Feeding and Spacing:
The feeding and foraging characteristics of the Emperor tamarin are well studied and very consistent trends are common amongst the population. Tamarins are omnivores and their food of choice is fruit. But they have been known to eat insects and even gums during the dry season. Their foraging and food hunting skills are remarkably advanced and they have adapted interspecific relationships to enhance their success. The benefits have outweighed the costs and contribute the widespread trend (Marques 2003).
Tamarins form mixed-species troops to help aid in the location, predator detection, and defense of the food patches. The main drawback is the cost of increasing number of group members and the obvious lack of sufficient fruit available. This proves to be a lesser concern for the Emperor Tamarin due to their social dominance over other tamarin species and maintain priority over discovered fruits. It has been observed, that inter-specific groups share information about food location as well (Marques 2003)
The behavior associated with the finding and defending of multiple food areas within a range is directly related the spacing patterns and interactions amongst tamarins. Some species of tamarin are known to spend upwards of 80% of their day in mixed-species groups. However, Emperor Tamarins spend roughly 20% of their day in groups. This due to the fact that inferior species disperse before long since the Emperor enforces its dominance over the food supply (Marques 2003, 2004). They use a particular food source and return to it again. Often, these patches are defended by groups and their use is rotated to prevent the exhaustion of a single source. Preferably, groups spaced within range of auditory warnings and alerts are often favorable plots (Marques 2004).
Tamarins, like other Callitrichines form polyandrous relationships in which a dominant female lives in small groups and mates with all of the males in it. This is done for a multitude of reasons but it provides an efficient solution to the problems associated with the high costs of birthing and raising their young. Callitrichines carry a greater burden raising their young than other primates (Rylands, 1996.) Thus, it makes sense that certain techniques have been implemented to help manage these costs (Garber, 1993.)
Tamarins are unique in that 80% of births are twins and it is not uncommon for triplets to be born as well. This unique characteristic is one major contributor to the unusually great cost of raising offspring. In addition, like other primates, they have a relatively long gestation period of 140-145 days and are not even weaned until around three months. The cost of these factors is complicated further by the added stress of carrying their young in an arboreal environment. Carrying young leads to an 11% decrease in body weight due to the large amount of time devoted to this activity (Mitani, 2008.)
Although some studies have shown pairs of tamarins to successfully raise their young, these are undoubtedly not the preferred conditions amongst the species (Garber, 1993.) The tamarin lifestyle fits with the proposed evolutionary causes of cooperative polyandry. The amount of older individuals in the group is low and thus less help is available for raising young. This has lead to the recruitment of other males to stay and perform these tasks. Without this help, tamarins would not have the reproductive success that they do today. This current system carries far more advantages than otherwise and will likely remain unaltered since the adoption of this mating system has been a crucial part in the success of the species (Mitani, 2008.)
Grouping Patterns and Kinship:
Tamarins display highly developed social systems and grouping patterns unique from other non-callitrichine primates. The majority of their behavior carries an evolutionary primer and has led to the overwhelming success of this species. However, certain behaviors exist more or less as a component of bonding amongst the group but are nevertheless a crucial part of the tamarin lifestyle (Rylands, 1996.)
In many ways tamarins form a very close-knit family with the other group members. They all take part equally in raising young, and aside from a dominant female, very little hierarchy of dominance exists. The father of the infant has no special role in the care of his child and often the true father is not known due to the multiple-male mating trends of the female (Garber, 1994.) Although the true parental figures are not always clear judging from behavior, no incest occurs within the system.
This type of parent-child relationship can be viewed alternatively in that this introduces a lack of kinship amongst families. However the tamarin, like other callitrichines, uses this way of life as an added component by which their group may improve its quality of life. Aside from the added safety and foraging success of the group, this provides a general foundation for which intimacy may be established within the group. Activities like grooming, playing, and carrying the young are common methods of social interaction.
The benefits of this grouping behavior arise from predator protection, foraging, and reproductive success. These more than outweigh the risks for the group, which are very little, including the possible shortage of food sources for the entire group (Mitani, 2008.) Even this obstacle has seemed to have been avoided by the Emperor Tamarin due to its inter-species grouping with less dominant tamarins (Rylands, 1996.)
Dispersal and Social Relationship:
Tamarins are known to interact within groups in several ways drastically improving their viability. Many of the relationships formed decrease the fitness of individuals but nonetheless contribute significantly to the survival of the group as a whole. These relationships contribute to the continued success of the Tamarin.
The commonly observed interaction amongst tamarins is strong group bonding. This serves the tamarin on several fronts; it allows the burden of child care to be spread out amongst all the members in the group. Most of the members are male and, contrary to common belief, does not lead to competition within the group. In fact, the task of carrying and caring for infants leads to bonding amongst the males to such a point that the true father of the infant is often unclear (Mitani, 2008.)
Although an individual tamarin may become less likely to survive and flourish while taking care of an infant, the inclusive fitness of the group is greatly improved and thus accounts, in part, for the success of this species. Further advantages of group living and moderate dispersal behavior are demonstrated during predator detection and location and defense of food, to name a few. However, the large birth burden remains the primary causal factor in the evolution of the majority of the interaction (Garber, 1994.)
The evolution of such behavior may have multiple causes. Likely, the birthing of twins and the extensive cost of raising and caring for the young has lead to the common bonding amongst male tamarins in the group taking on the role of a father figure (Mitani, 2008.) The advanced warning techniques within groups have lead to better predator detection. Larger groups also have better success in locating and defending food patches within their range (Marques, 2003.)
The benefits reaped from the formation of these tight-knit groups and the resulting social interactions in general have all contributed to the great success of the species. Undoubtedly, survival and prosperity of individuals would drastically decline without the inclusive fitness earned via these crucial interrelationships and bonding.
Social Behavior Problem Related to Tamarin:
The tamarin mating system of polyandry gives them a high reproductive success. However, this same system also leads to competition and resultant violence in the groups. In zoos, it was observed that mother’s often kill adult daughters. Such female-female attacks are also seen in the wild. Adult females instantly attack outside females trying to join their group (Cohn, 1997). This intolerance towards competition from outside female is turned towards the daughters in captivity when the mother feels competitive pressure from her own daughter.
Usually, females in the group do not leave the group even after they mature. Also, groups often have mature ovulating females who do not get pregnant. It is extremely rare to find ovulation without pregnancy in primates. The female-female aggression prevents the offspring from mating with dominant male in the group. Joining another group is out of question since the dominant female is bound to kill a new female trying to join the group (Cohn, 1997). Under these circumstances, it would seem that the only way a female can reproduce is after the death of the dominant female in the group. This would be an extremely inefficient way to reproduce.
One hypothesis for this female-female aggression is that the dominant female uses such aggression to defend her breeding position. While it helps the dominant female protect her place in the group, other females find it extremely difficult to find a mate in such situations. This would be contrary to the natural instinct of the primate to reproduce and should lead to lower rate of reproduction. Also, the female breeds only one or two times in a year and gives birth to twins or triplets at a time. So allowing other females in the group to breed would improve the chances of the dominant female to pass on her genes through her daughter’s generation. But the jealous protection of her breeding rights in the group means that the daughter has no chance. However, the high reproductive success of tamarins suggests that this monopoly of the dominant female on the males of a group has a reproductive advantage which is not obvious.
So the dominance of just one female in a group has to help the reproductive system of the tamarins in some ways other than simple protection of breeding right. Studies have shown that an adult female’s best chance of mating is by staying within the group. While the dominant female attacks a new female she is open to new males in the group. Such unrelated males can mate with the mature females in the group. As a result, some groups in the wild often have more than one breeding females.
But even in the wild, only 11% of the groups have two breeding females (Cohn, 1997). When females leave the group, they fail to find a new territory or gain entry into a new group. About 70% of such females die or disappear. The situation forces us to ask the question about how female tamarins manage to find mates, and that two more than one.
Perhaps a clue can be found in the fact that all the mates of the dominant female in a group are often siblings. As we saw earlier, all members of a group participate in bringing up the infant. During this process, the elder siblings get parental practice. My hypothesis is that the elder male siblings form partnership and may together join a new group or form a new group. As discussed earlier, the dominant female is open to new male in the group. Also, the daughter’s best chance of reproducing is by staying within the group. So when such brother tamarins form partnership and enter a group, they can easily find one of the elder daughters who is ready to breed. Such a trio can then form a new group, or in the case where the population is extremely dense, it can result in a group with two breeding females.
Further Studies to Test the Hypothesis:
The research done on this feature of tamarin reproductive system is very limited and there is not much data available to prove this hypothesis. Further studies are required to test this proposed hypothesis. Any further studies in this regard can be conducted both by observing the primate population in captivity as well as those in the wild, though studying the animals in the wild will give a much better understanding of system.
When studying the tamarins in captivity, the scientists should introduce two unrelated males into a group and two brothers in another group to observe how the group reacts to the new entrants. In the wild, it will not be possible to conduct such experiments. However, it would be worthwhile to study the formation of new groups and check if all the males breeding with the dominant female are related or not. The data collected through such studies will help substantiate the proposed hypothesis of this essay.
The tamarin reproductive system is quite unique and there is not much information available on what makes it successful. The proposed study will help answer some of the questions related to tamarin reproduction and benefits of female-female aggression within the group to the reproductive success of the tamarins.
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