Environmental Uncertainty and Evolution of Physiological Adaptation in Colias Butterflies

A scheme has been 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 two or more environmental parameters are correlated, and at least one of these is of direct selective significance to the organism. For the Colias case, attention is focused on the relationships between the photoperiodic cycle, the thermal regime, and the phenotype of the butterfly. In some environments photoperiod will be a useful cue to the thermal regime; in others it will be less useful. 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 three populations of lowland Colias are analyzed in the context of this system. One can make fairly accurate qualitative predictions about physiological and genetic strategies in response to the physical environment for each population. Tests so far have borne out the predictions. In predictable seasonal environments, physiological adjustments to changing environments can limit loss in average fitness that would result from genetic tracking.