Competing dopamine neurons drive oviposition choice for ethanol in Drosophila

Significance Flies use fermenting fruit as a food source and a site for oviposition. One of the main metabolites of fermentation is ethanol. When provided with different choices in the laboratory, female flies prefer to lay their eggs on food supplemented with ecologically relevant concentrations of ethanol. We show that different subsets of dopaminergic neurons have opposing effects on oviposition preference. We propose that in the wild, this may be a mechanism by which flies choose oviposition sites that are optimal for offspring fitness and survival and that this choice is highly dependent on context. The neural circuits that mediate behavioral choice evaluate and integrate information from the environment with internal demands and then initiate a behavioral response. Even circuits that support simple decisions remain poorly understood. In Drosophila melanogaster, oviposition on a substrate containing ethanol enhances fitness; however, little is known about the neural mechanisms mediating this important choice behavior. Here, we characterize the neural modulation of this simple choice and show that distinct subsets of dopaminergic neurons compete to either enhance or inhibit egg-laying preference for ethanol-containing food. Moreover, activity in α′β′ neurons of the mushroom body and a subset of ellipsoid body ring neurons (R2) is required for this choice. We propose a model where competing dopaminergic systems modulate oviposition preference to adjust to changes in natural oviposition substrates.