Fruit flies of the Drosophila genus cannot puncturate undamaged fruit, thus they lay their eggs on overripe or decaying fruit with already damaged skin. The exception to the rule is Drosophila suzukii, a polyphagous pest native to Southeast Asia. Females of this species have a serrated ovipositor that can penetrate soft-skinned fruit enabling egg laying under the epidermis of healthy and ripening fruit. This distinctive ovipositor has allowed D. suzukii to access a new and rich trophic niche and explains why this species successfully invaded Europe and the Americas, becoming a significant worldwide pest of soft-skinned fruit crops.
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Besides the elongation of the organ, the evolution of the serrated ovipositor implied important changes in the ovipositor bristles. Some bristles, especially those that line up along each side of the organ distal margin, became bigger and harder, resembling saw teeth. Then, during recent evolution in the D. suzukii lineage, the number of these saw teeth-like bristles increased by several times, making the ovipositor effectively serrated.
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D. subpulchrella, the D. suzukii sister species, also exhibits saw teeth-like bristles in the ovipositor organ. However, it only has less than half of those present in D. suzukii. Taking the fact that these species can be crossed in the lab under certain conditions, we are using phenotype-based selection across successive backcross generations to introgress the D. suzukii ovipositor into the genomic background of D. subpulchrella. Our goal is to identify the genes underlying the evolutionary increase in the number of the saw teeth-like bristles by genomic introgression mapping.
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