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 develop a framework for discussing these issues that focuses on the questions: What is the form of the adaptive landscape relating fitness to phenotypic characters? How do such landscapes differ for evolutionarily related groups? I examine the evolution of wing pigment patterns and thermoregulatory behavior for butterflies in two subfamilies in the family Pieridae, with three principal results. First, I show that thermoregulation can be an important component of fitness in pierids, and that wing color and thermoregulatory behavior are important phenotypic characters determining thermoregulatory performance and the adaptive landscape. Second, I show how limits on possible variation in wing color and behavior constrain evolution within one subfamily of pierids, and how these constraints are set by the physical and biochemical mechanisms of adaptation. Third, I show how evolutionary innovation may have resulted from the addition of a new, behavioral dimension to the landscape, and how this addition has altered the functional interrelations among various elements of the wing color pattern. I suggest that comparative analyses of the form and determinants of the adaptive landscape may be useful in identifying evolutionary innovations, and complement theoretical analyses of evolutionary dynamics on such fitness surfaces.