Developmental trajectories of gene expression reveal candidates for diapause termination: a key life-history transition in the apple maggot fly Rhagoletis pomonella

Abstract

The timing of dormancy is a rapidly evolving life-history trait playing a crucial role in the synchronization of seasonal life cycles and adaptation to environmental change. But the physiological mechanisms regulating dormancy in animals remain poorly understood. In insects, dormancy (diapause) is a developmentally dynamic state, and the mechanisms that control diapause transitions affect seasonal timing. Here we used microarrays to examine patterns of gene expression during dormancy termination: a crucial life-history transition in the apple maggot fly Rhagoletis pomonella (Walsh). This species is a model system for host race formation and ecological speciation via changes in diapause regulation of seasonality. Our goal was to pinpoint the timing of the transition from diapause to post-diapause development and to identify candidate genes and pathways for regulation of diapause termination. Samples were taken at six metabolically defined developmental landmarks, and time-series analysis suggests that release from metabolic depression coincides with preparation for or resumption of active cell cycling and morphogenesis, defining the 'end' of diapause. However, marked changes in expression, including members of pathways such as Wnt and TOR signaling, also occur prior to the metabolic rate increase, electing these pathways as candidates for early regulation of diapause termination. We discuss these results with respect to generalities in insect diapause physiology and to our long-term goal of identifying mechanisms of diapause adaptation in the Rhagoletis system.