Revision of Aedini traditional classification from Tue, 2016-01-12 12:21

This site hosts the phylogenetic classification of tribe Aedini established by Reinert et al. (2009). In view of the aims of the MTI, this is the preferred classification. However, the site now also displays the modified “traditional classification” of the tribe recently proffered by Wilkerson et al. (2015). The phylogenetic classification remains the primary classification and the latter is provided as an alternative classification for the reasons enunciated below.

Wilkerson et al. reanalysed the morphological data of Reinert et al. (2009) using equal weighting (EW) (rather than implied weighting (IW) as used in the earlier study) to “gauge the stability” of the generic groupings of the latter authors. The result was the retention of all the genera as terminal taxa within an otherwise largely collapsed tree, similar to the results of Harbach & Kitching (2015) who applied recently developed more stringent methods of assessing clade support to reanalyse their previous morphological data set of Anophelinae (Harbach & Kitching, 2005). The point to be made here is that although the deeper relationships were lost, all of the generic-level taxa of Reinert et al. survived, thus supporting the integrity (monophyly) of all these groups. A further point to be made is that no large morphological data set analysed in any study conducted to date has provided strong support for deeper relationships, e.g. the phylogenetic studies of Anophelinae (Sallum et al., 2000; Harbach & Kitching, 2005; Collucci & Sallum (2007), Culicini (Harbach et al., 2012) and Sabethini (Judd, 1996; Harbach et al., 2007; Motta et al., 2007).

Differences between phylogenetic trees and classifications derived from them occur when taxonomists choose to recognise paraphyletic and/or polyphyletic taxa to preserve traditional nomenclature. The issue is how to deal with such groups. One way is to eliminate them, which usually requires new names and changes to categorical ranks in a classification; a second way is simply to leave the classification in an unnatural state. Reinert et al. (2004) chose the first way, and recognised all of the former subgenera of Aedes that were “weighting independent”, i.e. those that were common to the results of both EW and IW analyses, as genera to reflect monophyly and rank equivalence with Armigeres, Eretmapodites, Haemagogus, Heizmannia, Opifex, Psorophora, Udaya and Zeugnomyia (see Figure 17 of Harbach, 2007). Wilkerson et al. (2015) effectively chose the second way, and recognised all the genera of Reinert et al. (2009) as subgenera within a very large and highly polyphyletic genus Aedes to preserve a backbone traditional classification for convenience.

In the phylogeny of Wilkerson et al. (Figure 3), Aedes (presumably subgenus Aedes despite boldface indicating it is genus Aedes) is sister to Paraedes + Verrallina. Paraedes is afforded subgeneric rank whereas Verrallina is retained as a genus; thus, the authors, being traditional systematists, interpret Verrallina as a group morphologically very different from Paraedes, and this dissimilarity is the basis for recognising it as a genus. This clade alone (there are 13 problematic clades within a polytomy that contains all the genera of Reinert et al. except Psorophora) demonstrates the inconsistent application of the “equivalent rank” criterion that they claim to use (in part?) to recognise groups as genera or subgenera. Reinert et al. (2004) faced an identical problem with a clade comprised of Aedes (Alanstonea) and Eretmapodites. Two options were available: either raise Ae. (Alanstonea) to genus rank or treat it as a subgenus of Eretmapodites. They chose the first option because the support for the Ae. (Alanstonea) + Eretmapodites clade was very weak and the supporting characters were all homoplastic. As has been pointed out many times, and is clearly stated or otherwise evident in major taxonomic treatments, the majority of generic-level taxa in Aedini are diagnosed by combinations of characters (polythetically diagnosed), most of which are homoplastic, i.e. they can occur in many different taxa. Wilkerson et al. seem to ignore or conveniently forget that the traditional classification of Aedini is likewise based on unique combinations of homoplastic characters. They state that “most of the genera [of Reinert et al.] cannot be identified except by combinations of character states, i.e., they do not have simple, unreversed diagnostic character states”, which conceals the fact that this is also the case when the genera are reduced to subgenera.

Wilkerson et al. also failed to mention that Psorophora falls outside the large polytomy of other aedine taxa in their cladogram and is paired with genus Mansonia (probably due to the application of equal weighting rather than implied weighting  to the data set). This stands in stark contrast to the cladistic analyses of Reinert et al., and the analyses of other authors (e.g. Reidenbach et al., 2009), where Aedini was recovered as monophyletic.

The application of explicit methods of phylogenetic analysis often reveals weaknesses in traditional classifications, yet the explicit methodology may also often confirm the monophyly of taxonomic groups based intuitively on unique combinations of characters. Consequently, the main issue is not in recognising monophyletic groups per se, but deciding what taxonomic ranks should be assigned to such groups. For phylogenetic systematists, the acceptance of broad polyphyletic genus groups for convenience is not an option, and where groups are found to be paraphyletic or polyphyletic, it is justifiable to remove them from the classification and give equal ranks to their constituent monophyletic groups.

The way in which Wilkerson et al. translated their phylogeny into a classification is problematic. Despite the various criteria discussed by the authors, their classification seems to have been based on a determination to retain the traditionally recognised genera of Aedini. If the huge polytomy is taken to be genus Aedes, then some branches in that clade should not be afforded generic rank while others are recognised as subgenera. For greater consistency in ranking taxa within a large genus Aedes, the seven traditional genera included in the polytomy, i.e. Armigeres, Eretmapodites, Haemagogus, Heizmannia, Opifex, Udaya and Zeugnomyia, should be ranked as subgenera. Because their generic status is retained, a reasonable alternative course of action would have been to recognise all the generic-level taxa as genera, thus preserving the genera and subgenera of Reinert et al. (2009).

Taxonomists rank organisms into different categories based principally on the degree of apparent similarities and dissimilarities ‒ the greater the degree of similarity, the more closely two taxa are related. Despite the weak support for deeper relationships within the phylogeny of Reinert et al. (2009), the combinations of homoplastic morphological characters on the branches indicate broad degrees of similarity and dissimilarity, which in many cases parallel the intuitive assessments of relationships hypothesised in taxonomic publications. Based on this and the commentary above, the phylogenetic classification of Reinert et al. (2009) is retained herein as the principal classification of Aedini, and also because the data set on which it is based provides an excellent foundation for researchers and students who are interested in analysing species relationships, making group comparisons and testing evolutionary hypotheses. However, in as much as the results of Wilkerson et al. (2015) essentially confirm the results of Reinert et al., and the crux of disagreement seemingly only involves opposing opinions and choices about taxonomic ranking, their updated traditional classification is added to the MTI for practical purposes, i.e. to aid operational workers and non-taxonomists who are more familiar with the traditional polyphyletic concept of Aedes. A number of errors in the listings of formal and particularly informal taxonomic groups in Appendices S1 and S2 of Wilkerson et al. are also corrected in the modified traditional classification featured here.

Nevertheless, users of either of the two classifications must realise that while phylogenetic trees can provide insights into relationships, they may not correctly reflect evolutionary history – they are merely hypotheses to be tested and modified as more information becomes available. The traditional and phylogenetic classifications of Aedini are contrasted in the attached file.

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Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith