FLATT, T; Brown University, Providence: Juvenile Hormone as an Effector of Metamorphosis and Life History Transitions

Hormones, regulatory signaling molecules that coordinate multiple developmental and physiological processes, commonly play central roles in the coordination of life cycles, both among and within species. Life history transitions, for instance from larva to adult or from a non-reproductive to a reproductive state, are typically controlled by hormones, and genetic correlations and trade-offs among life history traits are often hormonally mediated. Some of the best examples for such integratory and modulatory endocrine effects are provided by the lipid-like juvenile hormones (JHs) in insects. JHs are now known to affect a remarkable number of processes and traits, including metamorphosis, behavior, reproduction, morphological polyphenisms, diapause, stress resistance, and aging. In my talk I will review and illustrate the manifold effects of JHs, the probably most versatile animal hormones, with an emphasis on the fruit fly Drosophila melanogaster, an organism amenable to both genetics and endocrinology. In particular, I will highlight the role of JH in modulating life history transitions in Drosophila and other insects. Evolutionary modifications of JH signaling have played a key role in the evolution of insect metamorphosis and life history. While JHs are most well known for their inhibitory effects on preadult development and metamorphosis, these functions are clearly evolutionarily derived. I will discuss potential ancestral roles of JHs and why JHs might have been co-opted for metamorphic regulation. I will argue that understanding how hormones regulate particular life history transitions such as metamorphosis might help us to understand how hormones regulate life history transitions in general.