Thermoregulation, Flight, and the Evolution of Wing Pattern in Pierid Butterflies: The Topography of Adaptive Landscapes

SYNOPSIS. This paper describes a case study of adaptation, constraint,and evolutionary innovation in pierid butterflies. I developa framework for discussing these issues that focuses on thequestions: What is the form of the adaptive landscape relatingfitness to phenotypic characters? How do such landscapes differfor evolutionarily related groups? I examine the evolution ofwing pigment patterns and thermoregulatory behavior for butterfliesin two subfamilies in the family Pieridae, with three principalresults. First, I show that thermoregulation can be an importantcomponent of fitness in pierids, and that wing color and thermoregulatorybehavior are important phenotypic characters determining thermoregulatoryperformance and the adaptive landscape. Second, I show how limitson possible variation in wing color and behavior constrain evolutionwithin one subfamily of pierids, and how these constraints areset by the physical and biochemical mechanisms of adaptation.Third, I show how evolutionary innovation may have resultedfrom the addition of a new, behavioral dimension to the landscape,and how this addition has altered the functional interrelationsamong various elements of the wing color pattern. I suggestthat comparative analyses of the form and determinants of theadaptive landscape may be useful in identifying evolutionaryinnovations, and complement theoretical analyses of evolutionarydynamics on such fitness surfaces.