Abstract
BackgroundWhen organisms are attacked by multiple natural enemies, the evolution of a resistance mechanism to one natural enemy will be influenced by the degree of cross-resistance to another natural enemy. Cross-resistance can be positive, when a resistance mechanism against one natural enemy also offers resistance to another; or negative, in the form of a trade-off, when an increase in resistance against one natural enemy results in a decrease in resistance against another. Using Drosophila melanogaster, an important model system for the evolution of invertebrate immunity, we test for the existence of cross-resistance against parasites and pathogens, at both a phenotypic and evolutionary level.MethodsWe used a field strain of D. melanogaster to test whether surviving parasitism by the parasitoid Asobara tabida has an effect on the resistance against Beauveria bassiana, an entomopathogenic fungus; and whether infection with the microsporidian Tubulinosema kingi has an effect on the resistance against A. tabida. We used lines selected for increased resistance to A. tabida to test whether increased parasitoid resistance has an effect on resistance against B. bassiana and T. kingi. We used lines selected for increased tolerance against B. bassiana to test whether increased fungal resistance has an effect on resistance against A. tabida.Results/ConclusionsWe found no positive cross-resistance or trade-offs in the resistance to parasites and pathogens. This is an important finding, given the use of D. melanogaster as a model system for the evolution of invertebrate immunity. The lack of any cross-resistance to parasites and pathogens, at both the phenotypic and the evolutionary level, suggests that evolution of resistance against one class of natural enemies is largely independent of evolution of resistance against the other.
Highlights
All organisms suffer from attack by natural enemies, and the vast majority will face more than one species of natural enemy, be it predators, herbivores, parasites and/or pathogens
We explored cross-resistance at the phenotypic level, when the actual immune response after infection by one parasite or pathogen has an effect on the immune response after infection by a subsequent parasite or pathogen, and at the evolutionary level where the ability to activate an immune response against one parasite or pathogen has an effect on the immune response against another parasite or pathogen
We found that successful larval encapsulation of parasitoid eggs has no effect on adult resistance to fungal infection, and larval infection with microsporidia has no effect on subsequent encapsulation of parasitoid eggs
Summary
All organisms suffer from attack by natural enemies, and the vast majority will face more than one species of natural enemy, be it predators, herbivores, parasites and/or pathogens. When organisms face attack by different types of natural enemies, e.g. by predators and parasites, the defense mechanism evolved as a response to selection by one natural enemy may have an effect on defense against a second one. Such cross-resistance can be positive, when resistance evolved in response to one natural enemy is effective against another one. Using Drosophila melanogaster, an important model system for the evolution of invertebrate immunity, we test for the existence of cross-resistance against parasites and pathogens, at both a phenotypic and evolutionary level
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