BELDEN, L.K.*; RUBBO, M.J.; WINGFIELD, J.C.; KIESECKER, J.M.; Pennsylvania State University; Pennsylvania State University; University of Washington; Pennsylvania State University: The effect of density on the hormonal stress response of wood frog tadpoles

High population density is thought to be a stressor for many animals. In amphibians, previous laboratory studies have suggested that in dense populations, tadpoles have higher levels of corticosterone, the main glucocorticoid �stress� hormone in amphibians. Corticosterone can have important impacts on a multitude of other physiological and behavioral responses, including disease susceptibility, growth and development, responses to predators and dispersal rates. Therefore population density, acting via this hormonal mechanism, could have important consequences for individuals. To assess the relationship between corticosterone levels and density in more natural settings, we utilized a capture stress protocol to examine the hormonal stress response in wood frog tadpoles (Rana sylvatica) maintained in large outdoor mesocosms at three different densities. In addition, we completed the same capture stress profile in 6 natural ponds (three high density and three low density). After one week in the mesocosms, there was an increase in corticosterone levels in tadpoles following one hour of confinement. However, density did not alter the mean levels of corticosterone obtained during the confinement period and baseline levels of corticosterone did not differ between the different densities. Similarly, density did not have a significant effect on baseline corticosterone or mean corticosterone levels obtained during the stress series in the natural ponds. Based on these data, we conclude that density effects on tadpole corticosterone levels may be minimal in natural populations of wood frogs.