Carvalho & Mirth, 2017

An animal’s metabolism changes throughout development, obliging the animal to coordinate its feeding behaviour with its stage-specific nutritional requirements. Previous studies in the fruit fly Drosophila melanogaster have demonstrated that the developmental transition known as critical weight alters the response to nutrition in larvae; starvation reduces survival and dramatically delays development in pre-critical weight larvae, whereas it shows more moderate effects on survival and accelerates development in post-critical weight larvae. We thus hypothesized that this change in sensitivity to nutrition might result in differences in feeding behaviour between the two stages. Using both no-choice and two-choice assays, we show that pre-and post-critical weight larvae have similar strategies for macronutrient balancing, both regulating protein intake at the cost of under or over-consuming carbohydrates. Despite these similarities, we find that pre-critical weight larvae regulate protein intake within more narrow limits than post-critical weight larvae. In addition, larvae of different stages show significant differences in the way they regulate macronutrient intake in the presence of bitter, potentially noxious compounds. Larvae differed in their avoidance of bitter substance according to stage. Whereas pre-critical weight larvae avoided bitter food, post-critical weight larvae responded to these compounds by consuming less. If larvae were forced to trade off between a higher quality diet tainted with quinine or caffeine versus a lower quality diet containing less protein, larvae of both stages showed similar avoidance strategies but pre-critical weight larvae maintained a more constant protein intake than their post-critical weight siblings. Altogether, our results show that the developmental transition at critical weight modifies larval feeding behaviour, providing us an inroad to the understanding of how developmental processes influence behaviour.