Date of Award
Doctor of Philosophy
The thrifty phenotype hypothesis proposes reduced nutrition alters the trajectory of development of metabolic regulatory systems to produce a phenotype better fitted to an environment of decreased later-life nutrient availability. Because organisms have physiological mechanisms for coping with poor nutrition, they may have sociobehavioral mechanisms as well. Aggressive behavior, especially in the context of feeding competition, may be advantageous in such environments. There could be an association between aggression and intrauterine growth restriction (IUGR), which can result from low maternal food intake during pregnancy. The main hypotheses of this study are  IUGR offspring demonstrate higher rates of aggressive behavior and  IUGR offspring attain higher ranks. Behavioral observations were conducted on 22 juvenile baboons (Papio sp., ages 3-5 yrs) living in groups. Male IUGR (n = 4) and female IUGR (n = 5) were offspring of mothers fed 70% the same feed eaten by control (CTR) mothers in pregnancy and lactation. CTR males (n = 8) and CTR females (n = 5) were offspring of mothers fed ad libitum. Some authorities recommend this moderate level of dietary restriction for health and longevity. Offspring have not experienced dietary restriction since weaning. IUGR, compared to CTR, showed significantly increased rates of aggressive behavior, especially threat displays. Differences were more dramatic in males than in females. IUGR baboons performed the affiliative display behaviors lipsmack and chatter at elevated rates too, perhaps to counteract the effects of increased aggressive displays. IUGR females exhibited increased rates of stereotypical chewing behavior, while IUGR males exhibited decreased rates of play behavior, possibly indicating elevated anxiety levels. There was only limited support for condition-based differences in rank. Elevated rates of aggression in IUGR baboons may reflect an aggressive behavioral phenotype that enhances fitness by improving access to resources. Alternatively, they could be a non-adaptive result of neurodevelopment with a potentially negative impact on fitness. Unraveling the dynamic relationship between experiences and development is essential for understanding how phenotypes are formed. This will improve the ability of mothers to assess benefits of different nutritional strategies, leading to healthier individuals not just during growth and development, but throughout life.
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