Phylogenetic comparison of endosymbionts with their host ants based on molecular evidence

Some Formicid ants have symbiotic intracellular bacteria in the epithelial cells of their midgut. These endosymbionts are believed to be derived from a common ancestor. A recent study revealed that endosymbionts of the ant ge nus Camponotus are closely related to Enterobacteriaceae, but their relatio nship to endosymbionts of other genera of ants is unknown. In this study, t he nucleotide sequences of 16S ribosomal RNA (rRNA) of endosymbionts and mi tochondrial cytochrome oxidase subunit I (COI) of their host were determine d in five genera of the subfamily Formicinae (Hymenoptera: Formicidae). Bas ed on these molecular data, we constructed phylogenetic trees in order to c haracterize the systematic position of the symbionts and to estimate the re lationship of symbionts and hosts. The analysis showed that the endosymbion ts were all connected with the Enterobacteriaceae but did not constitute a monophylitic group, while the three genera belonging to the tribe Camponoti ni, the endosymbionts and their hosts made a clade. The topologies of these trees were identical for the most part. These results suggest that the end osymbionts of ants have plural origins, and that in the Camponotini, ancest ral symbionts have coevolved with their host ants, which are so divergent t o several genera as to construct one tribe.