Effects of Stress and Social Rank on Linear Enamel Hypoplasia in Chimpanzees (Pan troglodytes) Alanna M. Dillon Department of Biological Sciences, York College Project Summary Linear enamel hypoplasia is a general stress indicator and it has been shown that social rank affects stress levels. Little information discusses LEH and social rank. I propose to study the effects of dominance on the expression of LEH in chimpanzees (Pan troglodytes). To examine this, the animals in the study will be observed to determine their social rank. Fecal samples will be collected to determine cortisol levels and blood samples will be taken to assess Ca levels. The animals will be anesthetized and their teeth will also be examined for the presence of LEH. Results will then be analyzed to determine if social rank has a significant effect on the expression of LEH. The relationship between stress physiology, dominance, and LEH expression will also be examined. The proposed research would extend our understanding of stress physiology and dominance and how these factors relate to LEH in social primates. Introduction Linear enamel hypoplasia (LEH) is a general stress indicator that is found in primates. LEH is a deficiency in enamel thickness that comes from physiological perturbations or stress during the secretory phase of amelogenesis (the process of enamel formation) (Guatelli-Steinberg 2000). Enamel consists of apatite crystals that contain calcium and phosphate. In hypoplasia, there is a lack of enamel. LEH is seen as horizontal grooves in the teeth that can be fairly inconspicuous to very noticeable. In wild chimpanzees (Pan troglodytes) the males are the dominant individuals and will protect their social group. They can be aggressive and may even practice infanticide. Chimpanzees in captivity have shown higher levels of stress in more subordinate individuals than those who are more dominant (Morell 1996). Great apes show the most LEH with % of the individuals expressing it (Guatelli- Steinberg 2000). My proposed research will explore possible relationships between LEH and the rank of an animal within a social group of chimpanzees. Methods Observation of Captive Chimpanzees (Yerkes Primate Research Center) n=100 Determination of Social Hierarchy SubordinateDominantIndividuals Rank using Batchelder-Bershad-Simpson scaling method Collect fecal samples Cortisol level (using Pantex CORTISOL (CORT) 125 I) Anesthetize animals Collect Blood Examine Animals Observe Teeth Ca ++ Physical Determine Level Appearance Presence of LEH (total plasma Ca ++ (count total # of with automated LEH defects) photometric methods) Objectives 1.) To determine if there is a relationship between social rank and LEH expression 2.) To determine if there is a relationship between LEH and stress physiology Prediction  I predict that subordinate animals will show signs of chronic stress and therefore have higher LEH expression Review of Literature  Humans that died as subadults or young adults had a higher frequency of LEH than those that died as adults due to increased stress (Stodder 1997).  LEH is a sensitive dental indicator of physiological stress and that the defects provide a permanent and retrospective record of stresses (Guatelli-Steinberg 2000).  A relationship between social rank and stress physiology, as shown by fecal cortisol, has been found in primates (Cavigelli 1999).  Sexual, reproductive, courtship, parental, aggressive, and feeding behaviors can influence the levels of hormones present in an animal and hormones are associated with rank (Koren et al. 2002). Literature Cited Cavigelli, S.A Behavioural patterns associated with faecal cortisol levels in free-ranging female ring-tailed lemurs, Lemur catta. Animal Behaviour 57: Guatelli-Steinberg, D Linear enamel hypoplasia in gibbons (Hylobates lar carpenteri). American Journal of Physical Anthropology 112: Koren, L., Mokady, O., Karaskov, T., Klein, J., Koren, G. and Geffen, E A novel method using hair for determining hormonal levels in wildlife. Animal Behaviour 63: Morell, V Life at the top:animals pay the high price of dominance. Science 271:292. Stodder, A.L.W Subadult stress, morbidity, and longevity in latte period populations on Guam, Mariana Islands. American Journal of Physical Anthropology 104: Acknowledgements Dr. Bradley Rehnberg Expected Results  Subordinate animals will have higher stress levels (Morell 1996), therefore I would expect that as social rank decreases, the presence of LEH would increase (Figure 2).  Due to higher levels of stress, I would expect the presence of LEH to increase with an increase in cortisol level (Figure 3). Establish Rank Establish Rank Body Weight Figure 2. Correlation between rank and LEH expression in chimpanzees. Figure 3. Correlation between cortisol level in feces and LEH expression in chimpanzees. Figure 1. Linear enamel expression in lower canines of gibbon specimens.