Phylogenetic relationships between flies of the Tephritinae subfamily (Diptera, Tephritidae) and their symbiotic bacteria

The Tephritinae is considered the most specialized subfamily of fruit flies, predominantly infesting flowerheads of Asteraceae. Some species are known to host specific non-culturable symbiont bacteria ("Candidatus Stammerula spp.") in the midgut. In this work we (i) examined the phylogenetic relationships among the insect hosts, (ii) investigated the presence of bacteria in other hitherto unexamined species, and (iii) evaluated the phylogenetic congruence between insects and symbionts. A total of 33 Tephritinae species in 17 different genera were analyzed. Two regions of the mitochondrial DNA (16S rDNA and COI-tRNALeu-COII) were examined in the insect host, while the 16S was analyzed in the bacteria. From the phylogenetic trees, four of the five tribes considered were statistically supported by each of the clustering methods used. Species belonging to the tribe Noeetini never clustered at significant levels. The phylogenetic COI-tRNALeu-COII tree showed internal nodes more highly supported than the 16S phylogeny. The analysis of the distribution of symbiosis across the subfamily has highlighted the presence of bacteria only in the tribe Tephritini and in the genus Noeeta from the tribe Noeetini. A cophylogenetic analysis revealed a substantial congruence between hosts and symbionts. The interesting exceptions can be justified by events like losses, duplications and hosts switching opportunities, which are likely to arise during the biological cycle of the fly in consideration of the extracellular status of these symbionts.