CHIRONOMOIDEA, Macquart, 1838

Sinclair, Bradley J., Borkent, Art & Wood, D. Monty, 2007, The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance, Zoological Journal of the Linnean Society 150 (4), pp. 711-742 : 736-737

CHIRONOMOIDEA MONOPHYLY

Support for the monophyly of the Chironomoidea (sensu Wood & Borkent, 1989) has been based on the following morphological characters.

Prothoracic larval prolegs present

( Wood & Borkent, 1989)

This was originally proposed as a synapomorphy of this lineage due to its presence in Thaumaleidae , Simuliidae , Chironomidae , and early lineages of Ceratopogonidae ( Forcipomyiinae and first-instar Culicoides ) ( Wood & Borkent, 1989). More recently, prolegs have been observed in the first-instar larva of Corethrella appendiculata Grabham by Borkent & McKeever (1990). They suggested that the presence of the prothoracic prolegs was probably a synapomorphy of the entire Culicomorpha . Additional first instars of all lineages of the Culicomorpha should be examined.

Presence of procerci ( Wood & Borkent, 1989) Cylindrical processes bearing setae are present only in Chironomidae and Thaumaleidae , and assumed to be secondarily lost in Simuliidae and Ceratopogonidae ( Wood & Borkent, 1989) . Oosterbroek & Courtney (1995) doubted the value and homology of this character. This character appears weak and does not confidently support the monophyly of the Chironomoidea . The homology of the posterior segments of nematocerous Diptera requires a careful morphological study to determine homologous character states. The paired dorsal setae in Austroconops are possibly homologous to the procerci of Chironomidae ( Borkent & Craig, 2004: fig. 2C–G), but this remains speculative at this point.

Last abdominal segment bearing crochet-tipped posterior prolegs ( Oosterbroek & Courtney, 1995) Oosterbroek & Courtney (1995) considered the presence of crotcheted posterior prolegs as a synapomorphy of the Chironomoidea , but scored the ‘hooked spines’ in Corethrellidae and Chaoboridae as questionably homologous. We disagree with this interpretation and consider that the details of the ‘hooked spines’ of Corethrellidae and Chaoboridae are almost certainly homologous to those of Chironomoidea . They are in paired groups and their detailed structure is virtually identical.

The presence of anal prolegs is quite widespread and possibly subject to homoplasy among aquatic families. Within the nematocerous Diptera , posterior prolegs are otherwise present in Tanyderidae and Nymphomyiidae and similar structures are also known in Nannochoristidae ( Oosterbroek & Courtney, 1995) . Consequently, posterior prolegs may be a ground plan condition of Diptera , but the homologies of this character require careful interpretation. Wood & Borkent (1989) interpreted the presence of posterior prolegs as plesiomorphic for the Chironomoidea . Similar hooked spines are known in the Siphonaptera .

Preformed spermatophore ( Wood & Borkent, 1989) This character was originally proposed as a synapomorphy of Chironomoidea , exclusive of Thaumaleidae ( Wood & Borkent, 1989) . Sinclair (1992a) and the present study suggest that spermatophores are also probably produced in Thaumaleidae on the basis of the form of the male genital tract. The same evidence from this study also suggests that a preformed spermatophore is produced in Dixidae . Thus, it is highly probable that spermatophore production and the modified genital tract are ground plan features of the Culicomorpha , secondarily lost in Corethrellidae , Chaoboridae , and Culicidae (see ‘Culicoidea monophyly’).

Given our phylogenetic inferences, spermatophore production and the modification of the accessory gland into a multichambered complex are now viewed as synapomorphies for the Bibionomorpha + Ptychopteromorpha + Culicomorpha clade. Although no material of Tanyderidae was available, we predict that their male genital tract may be similarly modified.

It can be concluded from the above discussion of characters that there appears to be little or no support for the monophyly of the Chironomoidea , as already stated by Borkent & McKeever (1990). Evidence from the current survey does not definitely refute chironomoid monophyly, but simply moves previous synapomorphies (e.g. spermatophore production) down to the base of the Culicomorpha or deeper. Molecular evidence also has not supported the monophyly of the Chironomoidea . Pawlowski et al. (1996) tested the phylogeny of the Culicomorpha using partial 28S RNA gene sequences. Their results did not support the traditional subdivision of the Culicomorpha into two superfamilies, the position of Dixidae proved variable and Chironomidae appeared as a possible sister group to the remaining Culicomorpha . In another analysis, Miller, Crabtree & Savage (1997) tested the phylogeny of the Culicomorpha using 18S and 5.8S ribosomal DNA. The monophyletic clade Corethrellidae + Chaoboridae + Culicidae was resolved with the Chironomidae as its sister group. The Chironomoidea did not form a monophyletic group and the phylogenetic relationships of Ceratopogonidae , Simuliidae , and Dixidae were unresolved. Unfortunately a representative of the Thaumaleidae was not included in their study. In both of these studies, the taxon sampling was very limited and there was weak support for most internal nodes ( Yeates & Wiegmann, 1999).