LETTERSSpecializedcellstagsexualandspeciesidentityinDrosophilamelanogasterJean-ChristopheBilleter1,JadeAtallah1,JoshuaJ.Krupp1,JocelynG.Millar2&JoelD.Levine1Socialinteractionsdependonindividualsrecognizingeachother,andinthiscontextmanyorganismsusechemicalsignalstoindicatespeciesandsex1.Cuticularhydrocarbonsignalsareusedbyinsects,includingDrosophilamelanogaster,todistinguishconspecificindi-vidualsfromothers1–3.Thesechemicalsalsocontributetointraspe-cificcourtshipandmatinginteractions1–3.However,thepossibilitythatsexandspeciesidentificationarelinkedbycommonchemicalsignallingmechanismshasnotbeenformallytested.Herewepro-videdirectevidencethatasinglecompoundisusedtocommunicatefemaleidentityamongD.melanogaster,andtodefineareproductiveisolationbarrierbetweenD.melanogasterandsiblingspecies.Atransgenicmanipulationeliminatedcuticularhydrocarbonsbyablatingtheoenocytes,specializedcellsrequiredfortheexpressionofthesechemicalsignals.Theresultingoenocyte-less(oe2)femaleselicitedthenormalrepertoireofcourtshipbehavioursfrommales,butwereactuallypreferredoverwild-typefemalesbycourtingmales.Inaddition,wild-typemalesattemptedtocopulatewithoe2males.Thus,flieslackinghydrocarbonsareasexualhypersti-mulus.Treatmentofvirginfemaleswiththeaversivemalephero-monecis-vaccenylacetate(cVA)significantlydelayedmatingofoe2femalescomparedtowild-typefemales.Thisdifferencewaselimi-natedwhenoe2femalesweretreatedwithablendofcVAandthefemaleaphrodisiac(7Z,11Z)-heptacosadiene(7,11-HD),showingthatfemaleaphrodisiaccompoundscanattenuatetheeffectsofmaleaversivepheromones.7,11-HDalsowasshowntohaveacrucialroleinheterospecificencounters.Specifically,thespeciesbarrierwaslostbecausemalesofotherDrosophilaspeciescourtedoe2D.melano-gasterfemales,andD.simulansmalesconsistentlymatedwiththem.Treatmentofoe2femaleswith7,11-HDrestoredthespeciesbarrier,showingthatasinglecompoundcanconferspeciesidentity.Theseres