The conquest of a new habitat: A study of the nutritional and sensory adaptations of the D. suzukii larvae.
Authors: DIego Galagovsky; Ana Depetris-Chauvin; Markus Knaden; Bill Hansson
Affiliation: Max Planck Institute for Chemical Ecology
Keywords: c. nutrition; u. other (Drosophila spp)
Animals need to feed to incorporate nutrients –protein, carbohydrates, and lipids, to use as source of energy and as building blocks to maintain their bodies. However, feeding substrates contain nutrients in different proportions; therefore, depending on the specific needs of an organism, food sources will have varying nutritional quality. To assess their needs and feed accordingly, animals have both mechanisms to evaluate their internal needs, and mechanisms to sense for chemical cues in foods that hint at their nutrient content. However, for some organisms, it is not their decision where to feed, but that of their parents.
In the life cycle of Drosophila flies, we can distinguish two main feeding stages–the larva and the adult, with different objectives and nutritional needs. The larva feeds mainly to grow and accumulate resources for metamorphosis while the adult needs nutrients to survive and achieve reproduction. Adult D. melanogaster flies prefer to feed and lay eggs on protein-rich overripe fruits. These make a good feeding substrate for the larvae. Conversely, while D. suzukii adult flies also feed on overripe fruit, they are physically and behaviorally adapted to lay eggs on ripening fruits, which are harder and have a high sugar-protein ratio. D. suzukii larvae have to face the harsh nutritional landscape that has resulted from this novel adult behavior. How do they do it? Are the larvae physically adapted to this medium? How have their nutritional needs, their behavior and their physiology adapted to the shift in adult ecology?
I am addressing these questions at different levels; the nutritional composition of host fruits, the larval behavior, and the larval physiology.
Our results indicate that the environment in which D. suzukii larvae develop, the ripening fruit picked by their mother, is not a temporally homogeneous environment. It starts out as a sugar-rich, protein-poor environment, in which D. melanogaster larvae cannot survive. As the D. suzukii larvae process it, the protein content of the fruit increases. Their presence and activity also stimulate the fermentation of the fruit. By the time the larvae reach the late stages, the feeding substrate has become rich in proteins, enough to sustain D. melanogaster development. We have also observed that, compared to D. melanogaster, the 1st instar larvae of D. suzukii have massive mouth hooks, which aid them in processing the hard ripening fruit. Do D.suzuki larvae have special behaviors associated to the use of their physical adaptations? How does their physiology deal with the composition of the medium before they convert it? We are currently exploring the behavioral and physiological characteristics of the early larvae that allow them to develop in the ripening fruit.