Thermoregulatory Strategies in Colias Butterflies: Thermal Stress and the Limits to Adaptation in Temporally Varying Environments

Abstract

As a case study of adaptive strategies in temporally varying environments, thermoregulation in three populations of Colias butterflies along an elevation gradient in Colorado is studied in relation to the fluctuating meteorological environment. Emphasis is placed on short time scale (15-300 s) variation in air temperature and wind speed and its role in determining elevational patterns of body temperature, flight activity, and thermal stress due to overheating. A stochastic, linear filter model of an organism in a variable environment is used which views the adaptive process as the adjustment of the organism's filter. The relation-ship between this filter model and a transient energy balance model of the butterfly is examined to show how the thermoregulatory mechanisms of adaptation determine the filtering properties of the organism. Heat shocks at 45⚬ C significantly decrease survivorship and fecundity in Colias. Time series analysis indicates that short-term variation in wind speed and air temperature un...