In all vertebrates, responses to environmental perturbation are regulated to at least some degree by glucocorticoid hormones (GCs). In amphibians, GCs, along with several other hormones, also play an important role in larval growth and development preceding metamorphosis. Given these two well-established functions, GCs might be expected to have a role in the well-documented effects that environmental stressors can have on larval amphibian growth and development. However, while treatment with exogenous corticosterone (the main GC in amphibians) can alter growth and development in larval anurans, few studies have addressed the question of whether corticosterone levels achieved in the treatment are representative of levels in amphibians in the field. In this study, we examined physiological levels of corticosterone in Pacific Treefrog tadpoles (Hyla regilla) using a confinement stress protocol in the field and then examined the effects of exogenous corticosterone on growth of treefrog tadpoles in the laboratory. We found that treefrog tadpoles in the field did respond to confinement with increasing corticosterone levels. In addition, treatment with corticosterone in the laboratory resulted in decreased growth. However, the levels of corticosterone in our laboratory treated tadpoles were outside the range of what we have observed in wild animals. Although it is possible that these levels are still in the physiological range, they would be on the high end of what is observed in the field. We suggest that to understand the impacts of environmental stressors on larval amphibians via hormonal mechanisms, we must learn more about what the natural ranges of these hormones are in amphibians developing in the field.
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Vol. 2005 • No. 2