Environmental Uncertainty and Evolution of Physiological Adaptation in Colias Butterflies

Abstract

A scheme was devised for the consideration of interactions between environment and phenotype in uncertain environments. Although the discussion centers on the lowland species complex of Colias butterflies, it has general application wherever 2 or more environmental parameters are correlated. At least one of these is of direct selective significance to the organism. The relationships between the photoperiodic cycle, the thermal regime and the phenotype of the butterfly are examined. Several parameters are proposed as useful in evaluating the environmental uncertainty in this situation. Among these are the signal strength of the thermal cycle, weekly variance in temperature, and the slope (b) and coefficient of nondetermination (1-r2) of the phase-lag corrected regression of temperature on photoperiod. Both physiological and genetic mechanisms to deal with uncertainty are discussed. Environments of 3 populations of lowland Colias are analyzed in the context of this system. Qualitative predictions about physiological and genetic strategies are proposed in response to the physical environment for each population. In predictable seasonal environments, physiological adjustments to changing environments can limit loss in average fitness that would result from genetic tracking.