The endosymbiontWolbachiaincreases insulin/IGF-like signalling inDrosophila

Abstract

Insulin/IGF-like signalling (IIS) is an evolutionarily conserved pathway that has diverse functions in multi-cellular organisms. Mutations that reduce IIS can have pleiotropic effects on growth, development, metabolic homeostasis, fecundity, stress resistance and lifespan. IIS is also modified by extrinsic factors. For instance, in the fruitflyDrosophila melanogaster, both nutrition and stress can alter the activity of the pathway. Here, we test experimentally the hypothesis that a widespread endosymbiont of arthropods,Wolbachia pipientis, can alter the degree to which mutations in genes encoding IIS components affect IIS and its resultant phenotypes.Wolbachiainfection, which is widespread inD. melanogasterin nature and has been estimated to infect 30 per cent of strains in the Bloomington stock centre, can affect broad aspects of insect physiology, particularly traits associated with reproduction. We measured a range of IIS-related phenotypes in flies ubiquitously mutant for IIS in the presence and absence ofWolbachia. We show that removal ofWolbachiafurther reduces IIS and hence enhances the mutant phenotypes, suggesting thatWolbachianormally acts to increase insulin signalling. This effect ofWolbachiainfection on IIS could have an evolutionary explanation, and has some implications for studies of IIS inDrosophilaand other organisms that harbour endosymbionts.