Can the tight co-speciation between reed beetles (Col., Chrysomelidae, Donaciinae) and their bacterial endosymbionts, which provide cocoon material, clarify the deeper phylogeny of the hosts?

In most mutualistic symbioses of insects and intracellular bacteria, the endosymbionts provide additional nutrients to a host that feeds on an unbalanced diet. A strictly vertical transmission leads to co-speciation between the two partners. We have investigated an insect-bacteria relationship with a non-nutritional basis. The reed beetles (Donaciinae) harbor bacteria that produce a secretion used by the larvae for building a cocoon for pupation in mud underwater. The 16S rRNA of the bacteria and the cytochrome c oxidase I and elongation factor 1alpha of the beetles have been partially sequenced. The bacterial and the host phylogeny were highly congruent. Larger taxonomic units (genera) and host species groups/pairs have been recovered in the bacterial phylogeny. The symbiont data still cannot clarify the hitherto unresolved deeper phylogeny of the hosts, which is interpreted as a sign of rapid adaptive radiation of the reed beetles soon after their origin. The rate of sequence evolution among/within host species is discussed.