Evolution of heteroneuran Lepidoptera (Insecta) and the utility of dopa decarboxylase for Cretaceous-age phylogenetics

This study tests the utility of the nuclear gene encoding dopa decarboxylas e (DDC) for recovering Cretaceous-age divergences within the lepidopteran c lade Heteroneura, which contains 98% of lepidopteran species. A 709-bp frag ment of DDC has been sequenced in 32 species, including representatives of all major lineages of Heteroneura plus outgroups from more basal lepidopter an groups and the related order Trichoptera. Pairwise divergences across th e first and second codon positions and amino acids increase with depth thro ughout the taxonomic hierarchy, indicating that non-synonymous substitution s are not fully saturated; whereas, divergences across the third codon posi tion level off at the family to superfamily level. Inclusion of non-neolepi dopteran outgroups results in phylogeny estimates that contradict well esta blished groups, almost surely due to sparse taxon sampling and high charact er divergence. When these taxa and an equivalently divergent basal ditrysia n are excluded, DDC trees show nearly complete recovery of ten uncontrovers ial basal heteroneuran 'test clades' of family rank and higher, about half with strong bootstrap support. Thus, DDC clearly carries phylogenetic signa l at these levels. Bootstrap support for resolution of the controversial re lationships among the five main heteroneuran groups (four monotrysian super families plus Ditrysia) is individually low, but two of three previous hypo theses were statistically rejected overall by DDC. DDC trees within the pri mitive heteroneuran superfamily Incurvarioidea, though modestly supported, closely resemble a previous morphological hypothesis, while removing the re quirement for reversal in a possible 'key adaptation', the larval case. Tax on overlap with a previous mtDNA study of Prodoxidae (Incurvarioidea), whic h includes much-studied mutualist pollinators, permits a comparison of subs titution rates with the conservative mitochondrial COI+COII region, as well as combined-data re-examination of generic reltionships. Non-synonymous su bstitution is about 25% slower in DDC than in COI+COII, though synonymous s ubstitution is faster. With additional taxon sampling, and in combination w ith other genes, DDC promises to be a powerful tool for reconstructing amon g-superfamily relationships within Lepidoptera and probably other insect gr oups. (C) 2000 The Linnean Society of London.