Phylogenetic signal and its decay in mitochondrial SSU and LSU rRNA gene fragments of Anisoptera

The phylogeny of Anisoptera, dragonflies in the strict sense, has proven to be notoriously difficult to resolve. Based on morphological characters, se veral recent publications dealing with the phylogeny of dragonflies propose d contradicting inter- and intrafamily relationships. We explored phylogene tic information content of mitochondrial large-subunit (LSU) and small-subu nit (SSU) ribosomal gene fragments for these systematic problems. Starting at published universal primers, we developed primer sets suitable for ampli fying large parts of the LSU and SSU rRNA genes within dragonflies. These f ragments turned out to harbor sufficient phylogenetic information to satisf yingly resolve intrafamily relationships, but they contain insufficient phy logenetic structure to permit reliable conclusions about several interfamil y relationships. We demonstrate that decay of phylogenetic signal progresse s from intrafamily to interfamily to outgroup relationships and is correlat ed with an increase of genetic distances. As expected, signal decay is most pronounced in fast-changing sites. Additionally, base composition among fa st-changing sites significantly deviates from the expected homogeneity. Hom ogeneity of base composition among all included taxa was restored only afte r removing fast-changing sites from the data set. The molecular data tentat ively support interfamily relationships proposed by the most recent publica tion based on morphological characters of fossil and extant dragonflies.