Resolving relationships over a wide taxonomic range in Delphacidae (Homoptera) using the COI gene

Abstract. Using a combination of different methods to investigate the suitability of a fragment of the cytochrome c oxidase I gene (COI), we succeeded in partially resolving phylogenetic relationships in Delphacidae from the level of species to subfamily. Spectral analysis applied to the relatively noisy COI data proved to be especially useful. It clearly showed when phylogenetic signals were not completely randomized and it was very helpful for identifying problem areas in the dataset. Relationships among the four sampled subfamilies were completely resolved. In contrast to the tree based on morphological characters, we found evidence that Asiraca and Ugyops are sister groups (supporting monophyly of Asiracinae) and that Stenocraninae are the sister group of Kelisiinae. Contradictory signals were observed within Delphacini, but there are characters that support a close relationship between Conomelus and Megamelus. Other than this, the COI data gave support for the monophyly of Kelisiinae, Delphacinae, Chloriona and Javesella. Although third codon positions may appear to be saturated within the ‘modern’ Delphacidae (Delphacini), they still contain important phylogenetic signals at the deepest taxonomic level. The easiest explanation for this is the difference in amino acid usage between Asiracinae and non‐Asiracinae. Overall, this fragment of the COI gene seems to be useful for a rather wide taxonomic range in Delphacidae, except maybe for resolving generic relationships in the large tribe Delphacini.