Premating isolation is determined by larval-rearing substrates in cactophilic Drosophila mojavensis. V. Deep geographic variation in epicuticular hydrocarbons among isolated populations

Adult epicuticular hydrocarbon variation of 14 geographically isolated popu lations of cactophilic Drosophila mojavensis was assessed to further invest igate mechanisms of sexual isolation. Hydrocarbon transfer experiments demo nstrated that these compounds are part of the mate recognition system in th is species. Sixteen of the 23 epicuticular hydrocarbon components studied d iffered in amounts between males and females, and 13 differed in quantity b etween the geographic regions encompassing Baja California and mainland Mex ico (Sonora and Sinaloa). Eight hydrocarbon components, seven of which diff ered in quantity between sexes, showed significant sex-by-region interactio ns, indicating region-specific sex reversals in hydrocarbon quantities. Suc h regional variation in epicuticular hydrocarbon profiles suggests that the se hydrocarbon differences have also evolved in D. mojavensis since this sp ecies invaded mainland Sonora and Sinaloa from Baja California by switching host plants, in addition to a number of key genetic, behavioral, and life- history characters.