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COMPLEX FUNCTION OF THE CENTRAL NERVOUS SYSTEM, SLEEP AND LOCOMOTION
1Integrative Biology, University of Texas, Austin, Texas 78712; 2Department of Biology, Arizona State University, Tempe, Arizona 85287; 3Department of Zoology, University of Washington, Seattle, Washington 98915; 4Neurobiology, Physiology, and Behavior, University of California, Davis, California 95616; and 5Division of Biomedical and Clinical Laboratory Sciences, University of Edinburgh Medical School, Edinburgh EH8 9XD, Scotland, United Kingdom
Submitted 9 December 2002 ; accepted in final form 18 May 2003
We examined plasticity of the stress response among three populations of the white-crowned sparrow (Zonotrichia leucophrys). These populations breed at different elevations and latitudes and thus have breeding seasons that differ markedly in length. We hypothesize that in populations where birds raise only one or rarely two broods in a season, the fitness costs of abandoning a nest are substantially larger than in closely related populations that raise up to three broods per season. Thus individuals with short breeding seasons should be less responsive to stressors and therefore less likely to abandon their young. In our study, baseline and handling-induced corticosterone levels were similar among populations, but corticosteroid-binding globulins differed, leading to a direct relationship between stress-induced free corticosteroid levels and length of breeding season. There were also population-specific differences in intracellular low-affinity (glucocorticoid-like) receptors in both liver and brain tissue. Although investigations of population-based differences in glucocorticoid secretion are common, this is the first study to demonstrate population-level differences in binding globulins. These differences could lead to dramatically different physiological and behavioral responses to stress.
white-crowned sparrow; corticosterone; corticosteroid-binding globulin; corticosteroid receptor; reproduction
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