Evolutionary Insights into Taste Perception of the Invasive Pest Drosophila suzukii

Chemosensory perception allows insects to interact with the environment by perceiving odorant or tastant molecules; genes encoding chemoreceptors are the molecular interface between the environment and the insect, and play a central role in mediating its chemosensory behavior. Here we explore how the evolution of these genes in the emerging pest Drosophila suzukii correlates with the peculiar ecology of this species. We annotated approximately 130 genes coding for gustatory receptors (GRs) and divergent ionotropic receptors (dIRs) in D. suzukii and in its close relative Drosophila biarmipes. We then analyzed the evolution, in terms of size, of each gene family as well of the molecular evolution of the genes in a fourteen Drosophila species phylogenetic framework. We show that the overall evolution of GRs parallels that of dIRs not only in D. suzukii, but also in all other analyzed Drosophila. Our results reveal an unprecedented burst of gene family size in the lineage leading to the suzukii subgroup, as well as few genomic changes that characterize D. suzukii, in particular duplications and strong sign of positive selection in the putative bitter-taste receptor GR59d. Expression studies of duplicate genes in D. suzukii support a spatio-temporal sub-functionalization of the duplicate isoforms. Our results suggest that D. suzukii is not characterized by gene loss, as observed in other specialist Drosophila species, but rather by a dramatic acceleration of gene gains, compatible with a highly generalist feeding behavior. Overall, our analyses provide candidate taste receptors specific for D. suzukii which may correlate with its specific behavior and which may be tested in functional studies to ultimately enhance its control in the field.

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