Explaining consistent differences in social behavior between related taxa is a major goal of comparative socioecology, in which both ultimate (evolutionary, generally selective) and proximate (physiological) causal factors must be addressed. It is generally, and reasonably, assumed that species-specific behavioral traits, like other diagnostic aspects of phenotype, have distinctive genetic underpinnings that have evolved, mainly under the influence of natural selection. Observable interactions among individuals and the social structures that emerge from those interactions are, however, widely removed from the genetic level, and the physiological mechanisms linking genes to behavior are inadequately documented. Broadly speaking, in tracing back from the observable to the inherited, two sets of links are involved: first, between behavior and physiology and second, between physiology and heritage. The first has attracted considerable attention and effort, but the second has until recently been much less accessible, especially in primates and other socially complex animals. As long as this is so, the hypothesis that behavioral diversity has evolved by natural selection, rather than by "tradition" or other non-genetic transmission, though plausible, remains unproven. This project aims to differentiate factors that influence individual variation in reproductive and stress hormones and clarify the connection between heritage, endocrine physiology and social behavior. As a first step in this direction, this study will determine whether a significant proportion of variation in concentration of testosterone and glucocorticoids can be attributed to heritage in a large, genetically diverse, and fully pedigreed population of captive baboons (Papio hamadryas) derived from several subspecies. Study subjects are housed at the Southwest Foundation for Biomedical Research in San Antonio, TX. While captive conditions minimize variance in nutrition and other external factors, alternative caging arrangements (single-male, multi-female; all-male) partially simulate variation in social experience among male baboons in the wild. Fecal samples from 250 pedigreed, adult males will be collected and behavioral observations will be recorded to determine dominance rank. Testosterone and glucocorticoids will be extracted from the samples and measured for hormone concentration by radioimmunoassay. Hormone levels will be applied to the pedigree database to estimate the relative impact of heritage against a background of various social and environmental factors.
Recent major advances in socioendocrinology have concentrated on interactions between environmental factors, hormones, and behavior. This project will complement this work by focusing on the possible role of genetic factors in the interaction. This study will be the first to simultaneously investigate the genetic and non-genetic sources of individual differences in the concentration of steroid hormones (testosterone and glucocorticoids) under controlled environmental conditions. The research will integrate genetic, endocrine, and behavioral data in an interdisciplinary approach to the study of physiology and behavior fostering collaboration of academic and biomedical institutions by merging fields of quantitative genetics, socioendocrinology, and behavioral biology. Since baboons have provided analogies for human development, ecology, and evolution, this study has implications for the effects of genetic factors on physiological variability, and hence the potential for behavioral evolution, in humans and other primates. This project may also contribute to current research investigating the role of testosterone and glucocorticoids in human male development, health, and disease, perhaps directing future public health research toward factors underlying individual differences in reproductive and stress hormone concentration.
