Canadian Forest Service Publications

Epidemiology of asexuality induced by the endosymbiotic Wolbachia across phytophagous wasp species: host plant specialization matters.2014. Boivin, T.; Henri, H.; Vavre, F.; Gidoin, C.; Veber, P.; Candau, J.-N.; Magnoux, E.; Roques, A.; Auger-Rozenberg, M.-A. Molecular Ecology 23 (9): 2362-2375.

Year: 2014

Issued by: Great Lakes Forestry Centre

Catalog ID: 36547

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1111/mec.12737

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Among eukaryotes, sexual reproduction is by far the most predominant mode of repro- duction. However, some systems maintaining sexuality appear particularly labile and raise intriguing questions on the evolutionary routes to asexuality. Thelytokous parthe- nogenesis is a form of spontaneous loss of sexuality leading to strong distortion of sex ratio towards females and resulting from mutation, hybridization or infection by bacte- rial endosymbionts. We investigated whether ecological specialization is a likely mech- anism of spread of thelytoky within insect communities. Focusing on the highly specialized genus Megastigmus (Hymenoptera: Torymidae), we first performed a large literature survey to examine the distribution of thelytoky in these wasps across their respective obligate host plant families. Second, we tested for thelytoky caused by endosymbionts by screening in 15 arrhenotokous and 10 thelytokous species for Wolbachia , Cardinium , Arsenophonus and Rickettsia endosymbionts and by performing antibiotic treatments. Finally, we performed phylogenetic reconstructions using mul- tilocus sequence typing (MLST) to examine the evolution of endosymbiont-mediated thelytoky in Megastigmus and its possible connections to host plant specialization. We demonstrate that thelytoky evolved from ancestral arrhenotoky through the horizontal transmission and the fixation of the parthenogenesis-inducing Wolbachia . We find that ecological specialization in Wolbachia ’s hosts was probably a critical driving force for Wolbachia infection and spread of thelytoky, but also a constraint. Our work further reinforces the hypothesis that community structure of insects is a major driver of the epidemiology of endosymbionts and that competitive interactions among closely related species may facilitate their horizontal transmission

Plain Language Summary

We investigated asexual reproduction in the Megastigmus genus of insects (parasitic wasps). We wanted to further understand the evolutionary route of this phenomenon. We examined the literature to determine the incidence of thelytoky (a form of asexual reproduction where females are produced from unfertilized eggs) across host plant families. We believe it is caused either by mutation, hybridization or infection by bacteria from symbiotic organisms. We looked for bacterial causes by screening 10 thelytokus species and 15 arrhenotokous species (where unfertilized eggs develop into males) for symbiotic bacterial. We constructed an evolutionary tree and demonstrated that the Wolbachia species of bacteria had an important role. We conclude that ecological specialization by the hosts of these bacteria was a critical driving force for its infection and spread of thelytoky.