GLENNEMEIER, K.A.; DENVER, R.J.*: A Physiological Mediator of the Response to Intraspecific Competition in Rana pipiens Tadpoles

Competition is known to decrease growth and development rate in larval anurans, but the physiological mediators of this response have not been identified. We measured whole-body corticosterone content in Rana pipiens tadpoles raised at two different densities and three food levels. Both limited food and high density were associated with significantly elevated corticosterone content. Within the medium and low food treatments, high density decreased tadpole growth and slowed development, while within the high food group, high density was associated with greater growth and accelerated development (possibly an Allee effect). Lower food levels consistently slowed growth and development. Blocking corticosterone synthesis with metyrapone (MTP) reversed the effect of density on growth but not development and did not change the effect of limited resources on growth or development. Thus, corticosterone appears to mediate the effect of increased density on tadpole growth. These results are consistent with developmental studies that have shown high doses of exogenous corticosterone to affect growth but not development in pre-metamorphic tadpoles. Identification of such proximate mediators of tadpoles’ responses to their environment adds to our understanding of amphibian physiological ecology and could improve and simplify predictions about species interactions and their community-level outcomes. (Supported by the Great Lakes Environmental Protection Fund and NSF Grant IBN9974672).