Comparative thermal physiology of two sympatric sunfishes (Centrarchidae: Perciformes) with a discussion of microhabitat utilization

We investigated temperature-dependent responses of metabolism and thermal tolerance in bluegill (Lepomis macrochirus) and longear sunfish (L. megalotis). Each species showed significant differences in standard metabolic rate (SMR) and thermal tolerance among the three acclimation temperatures (10degreesC, 20degreesC, and 30degreesC). These sympatric centrarchids colonize microhabitats with different hydrodynamic and thermal regimes, which may be related to species differences in physiological responses to temperature. We found no interspecific differences in SMR and thermal tolerance. However, because there are differences in microhabitat utilization which may promote an adaptive suite of physiological tolerances unique to each species, we provide evidence suggesting that L. megalotis has greater physiological plasticity for SMR than L. macrochirus and that L. macrochirus has greater plasticity in thermal tolerance than L. megalotis. Trends in physiological plasticity with correlates of microhabitat utilization are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.