Evidence for Metabolic Provisioning by a Common Invertebrate Endosymbiont, Wolbachia pipientis, during Periods of Nutritional Stress

Top Cited Papers
Open Access
Publisher Website
Google Scholar
Abstract
Wolbachia are ubiquitous inherited endosymbionts of invertebrates that invade host populations by modifying host reproductive systems. However, some strains lack the ability to impose reproductive modification and yet are still capable of successfully invading host populations. To explain this paradox, theory predicts that such strains should provide a fitness benefit, but to date none has been detected. Recently completed genome sequences of different Wolbachia strains show that these bacteria may have the genetic machinery to influence iron utilization of hosts. Here we show that Wolbachia infection can confer a positive fecundity benefit for Drosophila melanogaster reared on iron-restricted or -overloaded diets. Furthermore, iron levels measured from field-collected flies indicated that nutritional conditions in the field were overall comparable to those of flies reared in the laboratory on restricted diets. These data suggest that Wolbachia may play a previously unrecognized role as nutritional mutualists in insects. Wolbachia are bacteria that infect millions of insect species worldwide. Wolbachia aren't infectious, but are maternally inherited symbionts passed from mother to offspring. To infect a host population, Wolbachia behave as reproductive parasites and alter the host reproductive system in a manner that increases infected female reproductive success. Some strains of Wolbachia, however, cannot manipulate their host's reproductive systems—yet they can successfully infect insect populations. How is this possible? Here we show that a Wolbachia strain that naturally infects Drosophila melanogaster, and induces very low levels of reproductive parasitism, can also act as a nutritional mutualist. When D. melanogaster flies were reared on normal diets, we observed no cost or benefit associated with the Wolbachia infection. But, if we reared flies on diets containing either very low or high amounts of iron, Wolbachia-infected flies produced more eggs than uninfected flies. As wild-caught flies contain low amounts of iron, our results suggest that flies in the wild should benefit from their Wolbachia symbiont.