Wolbachia bacteria, vertically transmitted intracellular endosymbionts, are associated with two major host taxa in which they show strikingly different symbiotic modes. In some taxa of filarial nematodes, where Wolbachia are strictly obligately beneficial to the host, they show complete within- and among-species prevalence as well as co-phylogeny with their hosts. In arthropods, Wolbachia usually are parasitic; if beneficial effects occurs, they can be facultative or obligate, related to host reproduction. In arthropods, the prevalence of Wolbachia varies within and among taxa, and no co-speciation events are known. However, one arthropod species, the common bedbug Cimex lectularius was recently found to be dependent on the provision of biotin and riboflavin by Wolbachia, representing a unique case of Wolbachia providing nutritional and obligate benefits to an arthropod host, perhaps even in a mutualistic manner. Using the presence of presumably functional biotin gene copies, our study demonstrates that the obligate relationship is maintained at least in 10 out of 15 species of the genera Cimex and Paracimex. The remaining five species harboured Wolbachia as well, demonstrating the first known case of 100% prevalence of Wolbachia among higher arthropod taxa. Moreover, we show the predicted co-cladogenesis between Wolbachia and their bedbug hosts, also as the first described case of Wolbachia co-speciation in arthropods.

Department of Biology University of Western Ontario 1151 Richmond Street London N6A 3K7 Ontario Canada

Department of Ecology Faculty of Environmental Sciences Czech University of Life Sciences Prague Kamýcká 129 CZ 165 21 Praha 6 Czech Republic

Technische Universität Dresden Department of Biology Applied Zoology D 01069 Dresden Germany

The Natural History Collections University Museum of Bergen P O Box 7800 N 5020 Bergen Norway

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