DoesDrosophila sechelliaescape parasitoid attack by feeding on a toxic resource?

Host shifts can drastically change the selective pressures that animals experience from their environment.Drosophila sechelliais a species restricted to the Seychelles islands, where it specialized on the fruitMorinda citrifolia(noni). This fruit is known to be toxic to closely relatedDrosophilaspecies, includingD. melanogasterandD. simulans, releasingD. sechelliafrom interspecific competition when breeding on this substrate. Previously, we showed thatD. sechelliais unable to mount an effective immunological response against wasp attack, while the closely-related species can defend themselves from parasitoid attack by melanotic encapsulation. We hypothesized that this inability constitutes a trait loss due to a reduced risk of parasitoid attack in noni. Here we present a field study aimed to test the hypothesis that specialization on noni has releasedD. sechelliafrom the antagonistic interaction with its larval parasitoids. Our results from the field survey indicate thatD. sechelliawas found in ripe noni, whereas anotherDrosophilaspecies,D. malerkotliana, was present in unripe and rotting stages. Parasitic wasps of the speciesLeptopilina boulardiemerged from rotten noni, whereD. malerkotlianawas the most abundant host. These results indicate that the specialization ofD. sechelliaon noni has indeed drastically altered its ecological interactions, leading to a relaxation in the selection pressure to maintain parasitoid resistance.