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.