Social Relationships
Image courtesy of Anne Savage
MALE/MALE or FEMALE/FEMALE RELATIONSHIPS:
The cotton-top tamarin does not exhibit specific male/male or female/female relationships. Instead, they work cooperatively within the social group. It is known that female cotton-top tamarins can have their reproduction suppressed by dominant females; however, researchers were unsure about whether male tamarins had similar experiences with dominant males. Therefore, researchers in the Snowdon laboratory examined the hormonal and stressful effects that dominant males had on the reproductive maturity of subordinate males in natal groups. They found that male cotton top tamarins experience normal, though longer, reproductive maturity within the cooperative breeding social group (Ginther et.al, 2002). These results are significant because they show that the female tamarins compete highly for the males and most of the selective pressure for a mate is placed on the female cotton-top tamarins. The reasons for such behaviors are not known. However, it can be inferred that there is more selective pressure for a mate in the females because they greatly rely on the males for parental care.
COOPERATIVE BREEDING BEHAVIORS:
The "helpers" in the cotton top tamarin social group care for the young for about 8 weeks afer birth, and the investment made in the young include carrying theyoung, caring for them when their parents' are foraging, protecting them from predators, and teaching them different social behaviors. As a group, the Callitrichids show the three main characteristics of cooperative breeding. These characteristics include: delayed reproduction of subordinates, allo-parenting, and delayed dispersal (Solomon, 1997). Cooperative behavior is thought to develop from kin selection, reciprocal altruism, or mutualism. However, there is not much information about the specific mechanisms that causes cooperative behavior to develop in the cotton-top tamarin (Cronin et.al, 2003). Snowdon and colleagues designed a study to examine the cooperative behaviors between cotton-top tamarins. They studied the ability of the cotton-top tamarin to work together by applying resistance to a transparent apparatus in which the tamarins had to pull simultaneously to receive an award. They found that the tamarins developed cooperative behavior as a cognitive adaptation (Cronin et.al, 2003). In addition, they were “aware of their partner's role in the cooperative actions and adjusted their behaviors to match those of their partners” (Cronin et.al, 2003).
In cooperative breeding, the members of the social group other than the parents help care for and raise the young. In addition, reproduction is limited to the dominant pair. Olfactory cues, hormones, and adrenal activity play an important role in suppression of ovulation within family groups (Solomon et.al, 1997). They help to increase the inclusive fitness of the dominant female and ensure reproductive success. In any cases, researchers have found that when female cotton-top tamarins were removed from their natal groups they began to experience their ovarian cycle and conceived (Ginther et.al, 2002).
SOCIAL BEHAVIORS BETWEEN MALES AND FEMALES:
When female tamarins are placed within the periphery of an unknown male tamarin, it has been observed that they increase their “affiliative behavior, copulations, and scent marking”. It is common to observe large amounts of contact, social huddling, and grooming between the pair. Male tamarins are groomed the most within the social group. In addition, it has been observed that juveniles play with each other more than adults. An increase in affiliative behavior is important in the establishment of pair bonds. Once the pair bonds are established, there is a decrease in affiliative behavior and the pair dedicates more time in caring for the young. However, their pair bond is still visible in territorial defense (Savage, 1990).
The
behavior of male and female cotton-top tamarins exhibit little sexual
dimorphism, but they differ greatly in behavior. Nevertheless,
there are conflicting views about the differences in behavior among
the sexes. Some researchers observed that males initiate contact, groom,
and sniff their mates more than females. However, other researchers
have found that there is no difference in the affiliative behavior
but females initiated sexual behavior more than males (Savage, 1990).
