Physiological cost induced by the maternally-transmitted endosymbiont Wolbachia in the Drosophila parasitoid Leptopilina heterotoma

Endosymbiotic bacteria of the genus Wolbachia infect a number of invertebra te species in which they induce various alterations in host reproduction, m ainly cytoplasmic incompatibility (CI). In contrast to most other maternall y transmitted parasites, manipulation of host reproduction makes the spread of Wolbachia possible even if they induce a physiological cost on their ho sts. Current studies have shown that fitness consequences of Wolbachia infe ction could range from positive (mutualist) to negative (parasitic) but, in most cases, Wolbachia do not have strong deleterious effects on host fitne ss and the status of association remains unclear. Here, we show that in the Drosophila parasitoid wasp Leptopilina heterotoma, Wolbachia infection has a negative impact on several host fitness traits of both sexes. Fecundity, adult survival and locomotor performance are significantly reduced, wherea s circadian rhythm, development time and offspring sex-ratio are not affect ed. Although the cost of bacterial infection can be overcome by effects on host reproduction i.e. cytoplasmic incompatibility, it could influence the spread of the bacterium at the early stages of the invasion process. Clearl y, results underline the wide spectrum of phenotypic effects of Wolbachia i nfection and, to our knowledge, Wolbachia infection of L. heterotoma appear s to be one of the most virulent that has ever been observed in insects.