Research Starter Grant

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Responding to stressful events in the environment is a fundamentally important activity for all organisms. Within the stress response, there is a plasticity of glucocorticoid action, allowing for specificity in the response depending on life history strategy, reproductive stage, body condition, or even time of day. This proposal explores the mechanisms, environmental regulation, and functional consequences of this plasticity among three subspecies of the white-crowned sparrow (Zonotrichia leucophrys gambelii, Z. l. oriantha, and Z. l. pugetensis). The three subspecies have different distributions that are likely to affect the evolutionary pressures shaping the stress response. In particular, these sparrows breed at different elevations and latitudes and thus have breeding seasons that differ markedly in length. Gambelii is the northern-most subspecies, breeding in the arctic and sub-artic regions of North America. The breeding season is short (allowing only 1 clutch per season). Oriantha breed in sub-alpine meadows of the western United States. They can raise one and sometimes two clutches per season. Pugetensis breeds at low elevations in the Pacific Northwest and usually raises 2 or 3 clutches per season. This proposal explores the possibility that the length of breeding season has a strong evolutionary influence on how birds respond to stress. Specifically, in birds with time to raise only one or rarely two clutches, the fitness consequence of abandoning the nest may be substantially larger than in birds that can raise up to three clutches per season. Thus, animals with short breeding seasons should be less responsive to stressors, and therefore less likely to abandon their young. The stress response of each subspecies will be evaluated measuring basal and stress-induced corticosteroid responses to capture and handling, corticosteroid binding globulin levels (to estimate the bioavailability of glucocorticoids), and glucocorticoid receptor levels (to estimate the tissue-specific sensitivity to glucocorticoids).