The Physiological Basis of Developmental Plasticity

Organismal form emerges from the relative growth of the body and its parts. In this dissertation, I address how developmental processes produce the size relationships between body parts that shape the characteristic morphologies of animals and plants. Specifically, I study the nutrition-dependent growth of wings in butterflies and moths to determine the developmental physiological mechanisms underlying morphological scaling relationships. Additionally, I dive into how form within a tissue is established by studying the mechanism that patterns growth of butterfly wings. Using an extensive data set from rats fed on a low protein diet, I analyze how different bones respond to nutritional variation and its effect on morphological integration. Finally, I end with a theoretical chapter discussing the ways in which development can be plastic and how that shapes both genetic and phenotypic evolution. I find that developmental plasticity emerges from changes in the concentration of systemic hormones in response to environmental stimuli. Hormones, in turn, interact with every developing part. This interaction is characterized by character-specific gene regulatory networks that affect their sensitivity to hormones. Thus, developmental plasticity emerges from the interplay between the organism sensing the environment that tunes the strength of a systemic signal that moderates development, and character-specific use of molecular networks that defines the range of character states in response to signal variation.