Meeting Abstract

37.5  Jan. 5  Pond desiccation rate affects immune system responsiveness in a temporary pond breeding amphibian, the wood frog (Rana sylvatica) GERVASI, S.S.; University of Michigan sgervasi@umich.edu

Theoretical studies and empirical data predict that life history strategies are often determined by variation in an organism�s environment. In response to environmental heterogeneity, many organisms have evolved some degree of plasticity in phenotypic expression. Phenotypic plasticity is especially prevalent among amphibians. For example, amphibians can avoid the direct threat of mortality due to pond desiccation by speeding up metamorphosis. This hormonally mediated response to pond desiccation is energetically expensive and may impose delayed costs. Energy directed toward the rapid completion of metamorphosis may be diverted away from the process of immune system development. Prometamorphic wood frog tadpoles were subjected to one of four desiccation regimes based on the rate of water removal. Each individual was subjected to a standardized immune system challenge at three weeks post metamorphosis. Phytohemagglutanin (PHA), a T-cell mitogen, was injected subcutaneously in all animals and caused a maximum skin swelling response within 24h. Individuals exposed to more rapid water desiccation regimes showed significantly faster developmental rates and significantly weaker skin swelling responses than individuals exposed to a constant, high volume of water. These results suggest that early stage stressors such as pond drying negatively impact certain aspects of immune system competence in metamorphs and possibly in juvenile and adult amphibians. These findings also imply that global climate change in the form of escalating climate variability may indirectly impact susceptibility of amphibians to a variety of emerging pathogens.