EVOLUTION AND PHYLOGENY OF THE DIPTERA - A MOLECULAR PHYLOGENETIC ANALYSIS USING 28S RDNA SEQUENCES

Portions of the large ribosomal subunit RNA gene (28S rDNA) encompassi ng the D1 and the D7 region were obtained from 16 dipteran species and families to reconstruct early phylogenetic events in the order Dipter a. For outgroup comparison, the corresponding sequences were used from representative taxa of the Siphonaptera, Mecoptera, and Lepidoptera. A subset of 488 unambiguously alignable sites was analyzed with respec t to important sequence evolution parameters. We found (1) sequence va riability is significantly higher in double-stranded sites than in sin gle-stranded sites, (2) transitions are close to saturation in most pa irwise sequence comparisons, (3) significant substitution rate heterog eneity exists across sites, and (4) significant substitution rate hete rogeneity exists among lineages. Tree reconstruction was carried out w ith the neighbor joining, maximum parsimony, and maximum likelihood me thods. Four major subgroups are consistently and robustly supported: t he Brachycera, the Culicomorpha, the Tipulomorpha sensu stricto, and t he hitherto controversial Bibionomorpha sensu late, which includes the families Sciaridae, Mycetophilidae, Cecidomyiidae, Bibionidae, Scatop sidae, and Anisopodidae. The phylogenetic relationships within or amon g these subclades and the positions of the families Psychodidae and Tr ichoceridae were not robustly resolved. These results support the view that the mouthparts of extant dipteran larvae evolved from a derived sound state characterized by subdivided and obliquely moving mandibles . Furthermore sequence divergence and the paleontological record consi stently indicate that a period of rapid cladogenesis gave rise to the major dipteran subgroups.