The role of development in the origin and evolution of adaptive phenotypic plasticity

Adaptive phenotypic plasticity is the environment-specific development of variation that enhances relative reproductive success. The occurrence of adaptive plasticity presents the opportunity to study the ecological conditions that favor the evolution and maintenance of phenotypic diversity within species, and provides a unique tool with which to study how developmental or proximate mechanisms shape the evolution of form.;Tadpoles of the spadefoot toads Spea bombifrons and S. multiplicatus may dramatically modify their behavior and morphology, changing from their typical omnivorous form into a rapidly developing and growing carnivore. In a series of empirical studies, I identified the conditions that induce these tadpoles to switch between alternative phenotypes, and I studied the effects of these discrete ontogenies on traits that contribute to reproductive success. Of greatest interest is my finding that the probability of developing the carnivore phenotype is highest when tadpoles are food stressed and an alternative food source, anostracan fairy shrimp, is abundant. This means that individual tadpoles assess their own condition and the abundance of alternative resources when responding to the cues that induce development of the carnivore phenotype; low-condition tadpoles become carnivores and increase their relative reproductive success by specializing on the unexploited fairy shrimp.;Such environmentally-cued polyphenisms illustrate that the environment in which an individual develops can affect the adult phenotype that is subject to selection. I develop a quantitative genetic model which demonstrates how interactions between the environment and proximate mechanisms regulating development can alter the distribution of phenotypes seen by selection, affecting the course of population evolution in the adaptive landscape. I then review how a research program that integrates the comparative method with quantitative genetics, embryonic manipulations, and molecular genetics has the greatest potential to elucidate how developmental processes affect the evolution of phenotypic plasticity in particular, and biological diversity in general.