NIJHOUT, Fred; Duke University: The Development and Evolution of Adaptive Polyphenisms

The ability to develop alternative phenotypes in response to specific environmental cues is called polyphenism. The developmental mechanisms underlying polyphenisms are now beginning to be understood. The development of alternative phenotypes comes about through environmentally induced changes in the patterns of hormone secretion. In insects, juvenile hormone and ecdysone, the same hormones that control metamorphosis, also control the morphology of the type adult a larva will become upon metamorphosis. These hormones produce their phenotypic effects during well-defined critical periods in development, by altering the patterns of gene expression during that time. The mechanism by which polyphenic development can give rise to evolutionary novelties will be discussed in the context of recent experimental work on the development and evolution of polyphenisms in insects.