Research |
My research focuses on hormonal mechanisms mediating behavior in free-living animals. This research integrates the classically disparate disciplines of behavior, endocrinology, physiology, ecology, and conservation. I emphasize a comparative and integrative approach and have worked on a wide variety of vertebrates (reptiles, amphibians, and birds) in a diversity of environments (arctic, deserts, and tropics). My research has two main aspects that are unique but also integrated. The first aspect of my research program addresses the behavioral and hormonal responses to stress and their interactions with reproduction. Animals are continually exposed to potential stressors in nature and appropriate physiological and behavioral responses are key to survival. The hormonal stress response includes the production of glucocorticosteroids from the adrenal cortex and is typically thought to suppress processes unnecessary for immediate survival, such as reproduction. However it is becoming increasingly clear that the negative relationship between stress and reproduction is not so simple and in free-living animals the challenges associated with reproduction can necessitate elevated levels of glucocorticosteroids. So far much of this work has been in snakes but in the future I intend to expand these studies of the interactions between stress and reproduction to anuran amphibians. This group is relatively understudied and exhibits many behavioral activities, such as territorial aggression and sound production, that are necessary for reproductive success yet are also extremely energetically expensive and are often associated with elevated plasma levels of glucocorticosteroids. With this group of animals I hope to elucidate general trends and mechanisms of the interactions between stress and reproduction in vertebrates. The second aspect of my research program investigates the seasonality and hormonal control of reproduction and territoriality in tropical birds. Research on tropical bird species has been sparse in comparison with temperate zone species, despite the fact that at least 2/3 of the world's bird species live in tropical regions. In temperate zone birds, changes in photoperiod are critical for timing reproduction and associated territorial aggression. In contrast to temperate regions, tropical zone environments experience minimal changes in day length. Thus, animals probably use other environmental cues to time seasonal processes. To investigate the cues that might be used for timing reproduction I am investigating the rufous-collared sparrows, Zonotrichia capensis, in Ecuador. This species is a congener to the well-studied northern latitude white-crowned sparrow and thus offers an excellent comparative opportunity. With these studies, I am attempting to elucidate the hormonal mechanisms that translate cues from the environment into seasonal territorial and reproductive behaviors through neuroendocrine systems.
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