Evolutionary shifts in taste coding in the fruit pest <i>Drosophila suzukii</i>.

Abstract

Although most <i>Drosophila</i> species lay eggs in overripe fruit, the agricultural pest <i>Drosophila suzukii</i> lays eggs in ripe fruit. We found that changes in bitter taste perception have accompanied this adaptation. We show that bitter-sensing mutants of <i>Drosophila melanogaster</i> undergo a shift in egg laying preference toward ripe fruit. <i>D. suzukii</i> has lost 20% of the bitter-sensing sensilla from the labellum, the major taste organ of the head. Physiological responses to various bitter compounds are lost. Responses to strawberry purées are lost from two classes of taste sensilla. Egg laying is not deterred by bitter compounds that deter other species. Profiling of labellar transcriptomes reveals reduced expression of several bitter <i>Gr</i> genes (<i>gustatory receptors</i>). These findings support a model in which bitter compounds in early ripening stages deter egg laying in most <i>Drosophila</i> species, but a loss of bitter response contributes to the adaptation of <i>D. suzukii</i> to ripe fruit.