Phylogenetic work in the strict sense on Diptera began with Hennig (1973) and Griffiths (1972). Only recently, numerical analyses have started to address the relationships within higher level taxa. Although molecular data has been used increasingly to reconstruct Dipteran phylogenies, most published analyses to date have focussed on questions at a lower-level, generally within particular infraorders. An exception is a recent detailed analysis of Brachycera relationships using over 2 Kb of 28S rDNA (Wiegmann and Yeates in prep.). The results of the last 30 years of phylogenetic research on the higher-level relationships of the Diptera using morphological data have been synthesised by us using supertree techniques. This Diptera supertree forms the framework for the following discussion.
The supertree generally supports recent research and shows that major dipteran higher categories such as Brachycera, Eremoneura, Muscomorpha, Cyclorrhapha, Schizophora, and Calyptrata are monophyletic. Conversely, a number of traditional higher taxa are paraphyletic based on morphological and molecular data. These include the Nematocera, Orthorrhapha, and Achiza. We therefore prefer to use the informal terms Lower Diptera, Lower Brachycera and Lower Cyclorrhapha for these groups. They represent evolutionary grades at the base of major radiations of Diptera, Brachycera, and Cyclorrhapha, respectively.
The paraphyly of the Lower Diptera has been suspected for decades, beginning with Hennig, and demonstrated in recent quantitative cladistic analyses using morphological data (Oosterbroek & Courtney, 1995). There have been only a few comprehensive phylogenetic analyses of the relationships between Lower Dipteran families using morphological and especially molecular data. The position of the tipulids and their relatives has been very unstable; some morphological treatments consider them the basal lineage of Diptera (Hennig, 1973), while others consider them to be closely related to Brachycera (Oosterbroek & Courtney, 1995). The supertree analysis currently favors Ptychopteromorpha+Culicomorpha as the sister group to the remaining Diptera with Blepharicerimorpha and Bibionomorpha being the next lineages to emerge from the Lower Dipteran stem. Close to the grade transition to Brachycera, the Lower Dipteran infraorders are not monophyletic, with Psychodomorpha and Tipulomorpha forming a paraphyletic grouping, the superfamily Tipuloidea being sister to the Brachycera. The arrangement of Tipulomorpha and Psychodomorpha represents a resolution of the incongruence between input trees.
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