Abstract
Background The relationships among the oldest winged insects (Palaeoptera), including the Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies), remain unclear. The Palaeoptera together with the Neoptera have evolved as result of a rapid divergence from a common ancestor in the distant past. Thus they are thought to be more susceptible to systematic inadequacies, including taxon sampling, choice of outgroup, marker selection, and phylogenetic methods. Here we reconstruct their phylogenetic relationship using newly sequenced mitochondrial genomes in combination with 90 additional insect mitochondrial genomes. In particular, we investigate the impact of the increased mayfly taxon sampling, the effect of rogue taxa, and the used phylogenetic framework (Bayesian inference (BI) vs. maximum likelihood (ML)) approach.
Results We found support for the clustering of the Odonata as most ancient, extant winged insects, using BI based on an optimized data matrix. Overall, we found no support for the basal Ephemeroptera clustering and the sister relationship between the Ephemeroptera and Odonata. Our newly sequenced mitochondrial genomes of Baetis rutilocylindratus, Cloeon dipterum, and Habrophlebiodes zijinensis showed the complete set of 13 protein coding genes and a conserved gene orientation with the exception of two inverted tRNAs for H. zijinensis.
Conclusions The increase of palaeopteran taxon sampling in combination with a Bayesian phylogenetic framework was crucial to infer phylogenetic relationships within the three ancient insect lineages of Odonata, Ephemeroptera, and Neoptera. Pruning of rogue taxa improved the number of supported nodes in all phylogenetic trees. It remains to be tested weather an increased taxon sampling might also reveal the elusive phylogenetic positions of other insect orders.