Distinct neural circuits establish the same chemosensory behavior in C. elegans

Animals frequently exhibit the same behavior under different environmental or physiological conditions. To what extent these behaviors are generated by similar vs. distinct mechanisms is unclear. Moreover, the circumstances under which divergent neural mechanisms establish the same behavior, and the molecular signals that regulate the same behavior across conditions, are poorly understood. We show that in C. elegans , distinct neural mechanisms mediate the same chemosensory behavior at two different life stages. Both dauer larvae and starved adults are attracted to carbon dioxide (CO 2 ), but CO 2 attraction is mediated by distinct sets of interneurons at the two life stages. Some interneurons mediate CO 2 response only in dauers, some show CO 2 -evoked activity in adults and dauers but contribute to CO 2 response only in adults, and some show CO 2 -evoked activity that opposes CO 2 attraction in adults but promotes CO 2 attraction in dauers. We also identify a novel role for insulin signaling in establishing life-stage-specific CO 2 responses by modulating interneuron activity. Further, we show that a combinatorial code of both shared and life-stage-specific molecular signals regulate CO 2 attraction. Our results identify a mechanism by which the same chemosensory behavior can be generated by distinct neural circuits, revealing an unexpected complexity to chemosensory processing.