Endosymbiont costs and benefits in a parasitoid infected with both Wolbachia and Cardinium

Abstract

Theory suggests that maternally inherited endosymbionts can promote their spread and persistence in host populations by enhancing the production of daughters by infected hosts, either by improving overall host fitness, or through reproductive manipulation. In the doubly infected parasitoid wasp Encarsia inaron, Wolbachia manipulates host reproduction through cytoplasmic incompatibility (CI), but Cardinium does not. We investigated the fitness costs and/or benefits of infection by each bacterium in differentially cured E. inaron as a potential explanation for persistence of Cardinium in this population. We introgressed lines infected with Wolbachia, Cardinium or both with the cured line to create a similar genetic background, and evaluated several parasitoid fitness parameters. We found that symbiont infection resulted in both fitness costs and benefits for E. inaron. The cost was lower initial egg load for all infected wasps. The benefit was increased survivorship, which in turn increased male production for wasps infected with only Cardinium. Female production was unaffected by symbiont infection; we therefore have not yet identified a causal fitness effect that can explain the persistence of Cardinium in the population. Interestingly, the Cardinium survivorship benefit was not evident when Wolbachia was also present in the host, and the reproduction of doubly infected individuals did not differ significantly from uninfected wasps. Therefore, the results of our study show that even when multiple infections seem to have no effect on a host, there may be a complex interaction of costs and benefits among symbionts.

Assessment of Survival and Body Size Variation of Culicoides imicola (Diptera: Ceratopogonidae) as Functions of “Candidatus Cardinium” (Bacteroidetes) Infection Status

“…While our results are limited to the effect of "Candidatus Cardinium" on its Culicoides host, it is possible that coinfection with other symbionts within the midge that were previously detected using denaturing gradient gel electrophoresis (DGGE) (7) and clone libraries (unpublished data) also may influence the observed results, as was shown for coinfection by "Candidatus Cardinium" and Wolbachia (1).…”

“…However, the fitness effect responsible for persistence of "Candidatus Cardinium" in the Encarsia population remained unclear (1).…”

“…Survival is known to be influenced by symbionts in multiple hosts (1,(17)(18)(19) and is a principal parameter in vectorial capacity (20,21). Adult body size is known to be linked with fitness characteristics, such as fecundity, survival, reproductive success, and blood feeding, in mosquitoes (22,23) and is an important fitness indicator in fruit flies (24).…”

Detection of Low-Level Cardinium and Wolbachia Infections in Culicoides

“…The cooccurrence of Wolbachia and Cardinium was detected in a number of individual Culicoides insects. Wolbachia and Cardinium are commonly seen to coinfect the same insect host species (57,63,64), but the nature of the interaction of these endosymbionts within the host insects can be unclear (65).…”

Wolbachiaincreases the susceptibility of a parasitoid wasp to hyperparasitism

“…To this end, the bacterium often has strategies to improve the overall fitness of its insect host. This has been found in some parasitoid wasps; for instance, Wolbachia benefits survivorship of the host Encarsia inaron (White et al, 2011). Asobara japonica wasps infected with Wolbachia show more efficient host (D. melanogaster)-searching ability (Furihata et al, 2015), while Wolbachia-infected Anagrus sophiae parasitoid wasps have higher reproductive success than uninfected individuals (Segoli et al, 2013).…”