DISSERTATION RESEARCH: Proximate Causes and Adaptive Significance of Individual Variation in the Behavior of Kangaroo Rats

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PROXIMATE CAUSES AND ADAPTIVE SIGNIFICANCE OF INDIVIDUAL VARIATION IN THE BEHAVIOR OF KANGAROO RATSDr. Stephen H. JenkinsAmy M. BarberComparative studies of closely related species or different populations of the same species have contributed greatly to our understanding of the evolutionary significance of various kinds of behavior. More recently, researchers have begun to focus on variation among individuals in the same population, especially individuals belonging to the same age and sex class. Study of this kind of variation holds as much promise for advancing understanding of the evolution of behavior in the future as study of interspecific variation and geographic variation within species has contributed to such understanding in the past. There are several recent reports of intraspecific variation in diverse behavioral traits. Some of this variation is organized into syndromes that are correlated with differences in hormone levels; these syndromes have been described as different strategies that may be important for how individuals interact with one another or their environment. However, most of this work has been done in the laboratory and so is unable to address how these different behaviors function under natural conditions.This study of Merriam's kangaroo rats (Dipodomys merriami) builds upon the current evidence by using an experimental approach in the field. Corticosterone is a major stress hormone in kangaroo rats and other animals and is an important basis, or proximate mechanism, for a variety of behaviors. Levels of corticosterone will be altered within the natural range for kangaroo rats using hormone implants of corticosterone to increase levels and metyrapone implants to decrease the natural production of corticosterone. These manipulations will be used to examine how individual differences in behavior change in response to changes in hormone levels. A newly developed technique for sampling hormones in the feces of rodents will be used to non-invasively measure differences in hormone profiles among individuals. The foraging behavior, spatial memory ability, and response of focal individuals to novel situations will be measured to quantify behavioral differences both before and after manipulation of hormone levels. In addition, the consistency of behavior will be characterized for focal animals. Modification of typical laboratory methods for use in the field will allow focal animals to remain in their natural habitat for a longer-term study; most importantly, the survival of individuals will be monitored in relation to their corticosterone levels and behavior over the course of the study. Survival is one key measure of the adaptive significance of behavior for kangaroo rats.This study, using a population of kangaroo rats in the field as a model system, provides a unique opportunity to understand in detail how individual variation in hormones influences the survival of individuals through its effects on a suite of interrelated behaviors. The study will also provide both graduate and undergraduate training.