Elusive ditrysian phylogeny: an account of combining systematized morphology with molecular data (Lepidoptera)

BACKGROUND: Ditrysia comprise close to 99 % of all butterflies and moths. The evolutionary relationships among the ditrysian superfamilies have received considerable attention in phylogenetic studies based on DNA and transcriptomic data, but the deepest divergences remain for large parts unresolved or contradictory. To obtain complementary insight into the evolutionary history of the clade, and to test previous hypotheses on the subdivision of Ditrysia based on morphology, we examine the morphology of larvae, pupae and adult males and females of 318 taxa representing nearly all ditrysian superfamilies and families. We present the most comprehensive morphological dataset on Ditrysia to date, consisting of over 500 morphological characters. The data are analyzed alone and combined with sequence data (one mitochondrial and seven nuclear protein-coding gene regions, sequenced from 422 taxa). The full dataset consists of 473 exemplar species. Analyses are performed using maximum likelihood methods, and parsimony methods for the morphological dataset. We explore whether combining morphological data and DNA-data can stabilize taxa that are unstable in phylogenetic studies based on genetic data only. RESULTS: Morphological characters are found phylogenetically informative in resolving apical nodes (superfamilies and families), but characters serving as evidence of relatedness of larger assemblages are few. Results include the recovery of a monophyletic Tineoidea, Sesioidea and Cossoidea, and a stable position for some unstable taxa (e.g. Epipyropidae, Cyclotornidae, Urodoidea + Schreckensteinioidea). Several such taxa, however, remain unstable even though morphological characters indicate a position in the tree (e.g. Immidae). Evidence supporting affinities between clades are suggested, e.g. a novel larval synapomorphy for Tineidae. We also propose the synonymy of Tineodidae with Alucitidae, syn. nov. CONCLUSIONS: The large morphological dataset provides information on the diversity and distribution of morphological traits in Ditrysia, and can be used in future research on the evolution of these traits, in identification keys and in identification of fossil Lepidoptera. The "backbone" of the phylogeny for Ditrysia remains largely unresolved. As previously proposed as an explanation for the scarcity of molecular signal in resolving the deeper nodes, this may be due to the rapid radiation of Ditrysia in the Cretaceous.