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Review of 'The evolution of head structures in lower Diptera'

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The evolution of head structures in lower Diptera

(2014)
The head of adult dipterans is mainly characterized by modifications and more or less far reaching reductions of the mouthparts (e.g., mandibles, maxillae), linked with the specialization on liquid food and the reduced necessity to process substrates mechanically. In contrast, the compound eyes and the antennae, sense organs used for orientation and for finding a suitable mating partner and oviposition site, are well developed. Some evolutionary novelties are specific adaptations to feeding on less liquefied substrates, such as labellae with furrows or pseudotracheae on their surface, and the strongly developed pre- and postcerebral pumping apparatuses. In some dipteran groups specialized on blood the mandibles are still present as piercing stylets. They are completely reduced in the vast majority of families. Within the group far-reaching modifications of the antennae take place, with a strongly reduced number of segments and a specific configuration in Brachycera. The feeding habits and mouthparts of dipteran larvae are much more diverse than in the adults. The larval head is prognathous and fully exposed in the dipteran groundplan and most groups of lower Diptera. In Tipuloidea and Brachycera the head is partly or largely retracted and the sclerotized elements of the external head capsule are partly or fully reduced. The head of Cyclorrhapha is largely reduced. A complex and unique feature of this group is the cephaloskeleton. The movability of the larvae is limited due to the lack of thoracic legs. This can be partly compensated by the mouthparts, which are involved in locomotion in different groups. The mouth hooks associated with the cyclorrhaphan cephaloskeleton provide anchorage in the substrate.
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    Review information

    10.14293/S2199-1006.1.SOR-LIFE.ALTCE1.v1.RJCCVG

    This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

    Review text

    The aim of the study was a formal evaluation of the character evolution and the reconstruction of the ordinal groundplan.

    The Authors, after having considered morphological characteristics of 76 adults
    and 70 larvae of numerous species of lower dipterans, by using confocal laser microscopy, hystological sections, microcomputer tomography and computer-based 3D reconstruction, have performed a cladistic analysis of these data.

    These findings were mapped onto the cladogram by Weigman et al (2011), the most comprehensive data set analysed so far, for a comparison.

    The paper is an extensive study which has taken into account many of the previous works on the head morphology of different insect groups, mainly Diptera.

    In the introduction, the Authors pointed out that while adults are relatively uniform in their morphology, larvae are highly variable not only in their structure but also in their life habitats and living environments.

    The phylogenetic results are somewhat unexpected as Tipulomorpha have always been considered the sister group of Brachycera or the sister group of the remaining Diptera, with the exclusion of the families of Deuteroplebiidae and Nymphomyiidae,on the basis of the wing venation of fossil and extant species, and of the structure of the pretarsus and of the wing stalk. From the analysis section, the authors note that Tipulomorpha turn out to be monophyletic as do Diptera Brachycera and Tipuloidea.

    From the analysis, Tipulomorpha result to be monophyletic as are Diptera Brachycera and Tipuloidea.

    In a section, the Authors have enlisted the potential apomorphies of several dipteran clades.

    From their study, the Authors have reached the conclusion that adult characters are not very conservative and are often affected by homoplasy. It appears that the adult head structures alone are not sufficient to reconstruct the intraordinal relationships. Also the larval head characters, however, are not sufficient to resolve the basal dipteran relationships as they are also strongly affected by homoplasy.

    The analyses indicate that Diptera are monophyletic when the complete data set and larval characters were considered, but not in the analyses of the adult head structures.

    The section dealing with the character transformations due to the adaptation to different life styles is very interesting. It is underlined that the most important modifications are those connected to the food uptake apparatus, the structure of the mandible and of the labium in particular. These modifications were allowed by the strong reinforcement of the head capsule.

    In conclusion the paper is a great help for anyone who wishes to investigate the Diptera Systematics and Phylogeny. This reviewer warmly recommend the paper for publication.

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