Adaptation of the invasive pest <i>Drosophila suzukii</i> to a specialized nutritional niche

Investigating the genetic basis of dietary adaptation provides insight into ecological specialization and the evolution of adaptive traits. Nutritional composition of available food sources varies substantially across ecological niches and plays an important role in shaping species distribution and adaptation. Unlike most Drosophila larvae that develop in decaying matters rich in protein and carbohydrate, the larvae of the invasive pest Drosophila suzukii thrive in fresh ripening fruits, a diet characterized by very limited protein and high carbohydrate levels. To understand the intrinsic nutritional adaptation of D. suzukii larvae, we examined its development and fitness on diets spanning a range of protein-to-carbohydrate (P : C) ratios and found that D. suzukii exhibits superior performance on low P : C diets compared to closely related D. biarmipes and D. melanogaster. Transcriptomic analyses showed that D. suzukii underwent fewer transcriptional changes on low P : C diets, with pathways associated with nutrient sensing, transport and digestion contributing to its adaptation. Functional validation in D. melanogaster confirmed that upregulating five genes-dilp3, sNPF, Oct-TyrR, Obp49a, and Dh31-enhanced larval fitness on low P : C diets, supporting their roles in D. suzukii's nutritional adaptation. Together, these results uncover intrinsic molecular mechanisms that enable D. suzukii larvae to successfully colonize a nutritionally challenging niche, and provide potential targets for its pest management strategies.