Mason Bennett and Dr. James Dee Higley, Psychology
Many species of primates have complex social systems and hierarchies. These social structures help in forming an identity and establishing a place in the world. Depending on one’s ranking in the social hierarchy there may be physiological, psychological, and emotional consequences. A primate with low rank may suffer greater stress, have less access to resources or social support, and have a higher chance of mortality (Sapolsky, 2004).
In the natural environment, rhesus macaques (Macaca mulatta) acquire social dominance rank through matrilineal family (mothers’) inheritance. In the laboratory setting at the California National Primate Research Center (CNPRC) the interactions and social structure of the macaques is somewhat artificial. Assignment to a troop or cage is done by researchers. Therefore matrilineal lines get split from each other and the conventional process of rank acquisition is tampered with. Currently the concept of social dominance is determined by a subordinance hierarchy. In a ratio of wins/losses those who are more victorious over their cage mates are determined to be higher in dominance (Bernstein, 1976).
Methods
Due to the generosity of an ORCA grant, student-researchers from Brigham Young University were able to travel to Davis, California and observe the rhesus macaques at the CNPRC. We sought to find a connection, similar to the natural setting, between mother’s dominance and their offspring’s dominance rankings later in life. Two outdoor field cages with a total of 200 macaques were observed. Observation teams consisted of three people; two observers and one recorder. Observers created food-elicited interactions, or confrontations, between monkeys by tossing seeds, vegetables, or grapes into the cages. Observers would then call out the ensuing interactions and the ID numbers of the monkeys involved. The recorder would write down the interactions and input the data once the session was over. Interactions included aggressive behaviors such as hitting, lunging, and chasing; as well as submissive behaviors such as lip-smacking, displacement, and fear-grimacing.
A dominance hierarchy was then set up based on a ratio of wins/losses observed. These ranks were z-scored and compared to the CPNRC’s Bio-Behavioral Assessment (BBA). The BBA, pioneered by John Capitanio, is performed over a 25 hour period when infants are 6 months of age, and includes a bio-behavioral battery of tests designed to measure temperament. See Capitanio, Mason, Mendoza, DelRosso, and Roberts (2006) publication for a full description of the BBA testing procedure. BBA subjects include 2,300 rhesus macaques raised at the CNPRC between the years of 2001-2012. Dominance rank was measured by wins/loses during head-to-head competition between all possible pairs in a group (Capitanio, 2013). Infant rank isn’t measured at this time but the mother’s rank is recorded in the database.
Results
From the 200 monkeys observed by BYU researchers 60 were also participants in the BBA testing. The 60 z-score ranks were compared to z-score ranks of the subject’s mothers. A bivariate correlation was done comparing the mother’s rank at the time of the BBA test to the offspring’s rank later in life. A correlation was found, r(58) = 0.4, p < 0.002.
Discussion
This shows that mother’s dominance is a predictor of the child’s dominance and the rank a child will carry with them later in life. Due to the correlation between mother rank and child rank our number of subjects has increased. We are now analyzing data from the BBA using mother’s dominance as a predictor for the infant’s dominance. This increases our subject pool from 60 subjects to 2,219. This demonstration of mother rank and child’s rank in the laboratory setting is consistent with macaque’s inheritance of social hierarchies in their natural environment. We are now continuing the research to ask whether the correlation between mother rank and child rank is a product of a socially advantageous environment provided by a high ranking mother or socially advantageous genes received from mother. We are also looking at what genetic, biochemical, and behavioral factors are linked to high and low dominance. The results of these questions are being prepared for the Utah Conference of Undergraduate Research, the Mary Lou Fulton Conference, the American Society of Primatologists Conference, as well as official publication in a scientific journal. I would like to thank Dr. Higley for his mentorship and guidance, as well as the CNPRC and John Capitanio for their assistance in this project as well as allowing us access to the monkeys and the BBA database.
References
- Bernstein, I. S. (1976). Dominance, aggression and reproduction in primate societies. Journal of Theoretical Biology, 60(2), 459-472. doi: dx.doi.org/10.1016/0022-5193(76)90072-2
- Capitanio, J. P. (2013). Codebook for the biobehavioral assessment program. Unpublished raw data, Biobehavioral characterization of infant rhesus monkeys R24OD010962.CNPRC P51OD011157
- Capitanio, J. P., Mason, W. A., Mendoza, S. P., DelRosso, L., & Roberts, J. A. (2006). Nursery rearing and biobehavioral organization. Nursery Rearing of Nonhuman Primates in the 21st Century (pp. 191-124). Retrieved from http://link.springer.com.erl.lib.byu.edu/chapter/10.1007/978-0-387-25640-5_11
- Sapolsky, R. M. (2004). Social status and health in humans and other animals. Annual Review of Anthropology, 33, 393-418. doi: 10.1146/annurev.anthro.33.070203.144000