title: Humidity Sensing in Drosophila.
abstract: Environmental humidity influences the fitness and geographic distribution of all animals [1]. Insects in particular use humidity cues to navigate the environment, and previous work suggests the existence of specific sensory mechanisms to detect favorable humidity ranges [2-5]. Yet, the molecular and cellular basis of humidity sensing (hygrosensation) remains poorly understood. Here we describe genes and neurons necessary for hygrosensation in the vinegar fly Drosophila melanogaster. We find that members of the Drosophila genus display species-specific humidity preferences related to conditions in their native habitats. Using a simple behavioral assay, we find that the ionotropic receptors IR40a, IR93a, and IR25a are all required for humidity preference in D. melanogaster. Yet, whereas IR40a is selectively required for hygrosensory responses, IR93a and IR25a mediate both humidity and temperature preference. Consistent with this, the expression of IR93a and IR25a includes thermosensory neurons of the arista. In contrast, IR40a is excluded from the arista but is expressed (and required) in specialized neurons innervating pore-less sensilla of the sacculus, a unique invagination of the third antennal segment. Indeed, calcium imaging showed that IR40a neurons directly respond to changes in humidity, and IR40a knockdown or IR93a mutation reduced their responses to stimuli. Taken together, our results suggest that the preference for a specific humidity range depends on specialized sacculus neurons, and that the processing of environmental humidity can happen largely in parallel to that of temperature.
authors.affiliation: Department of Biology, Lund University, 22362 Lund, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Enjin
authors.affiliation: Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Emanuela E
authors.initials: EE
authors.lastname: Zaharieva
authors.affiliation: Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Dominic D
authors.initials: DD
authors.lastname: Frank
authors.affiliation: Department of Biology, Lund University, 22362 Lund, Sweden.
authors.forename: Suzan
authors.initials: S
authors.lastname: Mansourian
authors.affiliation: Skirball Institute of Biomolecular Medicine, Neuroscience Institute, Department of Cell Biology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Greg S B
authors.initials: GS
authors.lastname: Suh
authors.affiliation: Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA. Electronic address: marco.gallio@northwestern.edu.
authors.forename: Marco
authors.initials: M
authors.lastname: Gallio
authors.affiliation: Department of Biology, Lund University, 22362 Lund, Sweden. Electronic address: marcus.stensmyr@biol.lu.se.
authors.forename: Marcus C
authors.initials: MC
authors.lastname: Stensmyr
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D006813:Humidity; D008297:Male; D009474:Neurons / Q000378:metabolism; D058468:Receptors, Ionotropic Glutamate / Q000235:genetics* / Q000378:metabolism; D012677:Sensation; D058618:Sensilla / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D058468:Receptors, Ionotropic Glutamate; C555767:ionotropic receptor 25a, Drosophila; C000625716:ionotropic receptor 40a, Drosophila; C000625717:ionotropic receptor 93a, Drosophila