Cretolixon, Lohrmann & Zhang & Michalik & Blaschke & Müller & Jeanneau, 2020
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publication ID |
https://doi.org/ 10.5194/fr-23-215-2020 |
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publication LSID |
lsid:zoobank.org:pub:3650519D-0470-42E2-97D7-A267658C0B4F |
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persistent identifier |
https://treatment.plazi.org/id/03E787A8-6A67-AD6F-FCD4-068805A3F980 |
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treatment provided by |
Felipe |
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scientific name |
Cretolixon |
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Cretolixon – a common ancestor of Rhopalosomatinae and Olixoninae?
As it would “undoubtedly” render the Rhopalosomatinae paraphyletic, Krogmann et al. (2009) argued against Engel’s subfamily classification, thus ignoring earlier morphological studies supporting a sister group relationship between the macropterous rhopalosomatids and the brachypterous Olixon , i.e., Brothers and Carpenter (1993), Brothers (1999), and Guidotti (1999). Brothers and Carpenter (1993) and Brothers (1999), based on their phylogenetic analyses, list nine potential synapomorphies for the Rhopalosomatinae. However, since most of these characters are not applicable to the morphologically aberrant Olixon it remains unclear whether these character states are novelties for the subfamily or whether they have evolved in the stem of the family with a secondary loss or derivation in the Olixoninae. The same might be true for the 22 characters received by Guidotti (1999) in her analysis of the generic relationships of rhopalosomatid wasps.
One of Guidotti’s potential apomorphies for the Rhopalosomatinae is a stiff apical bristle on the second labial palpomere ( Fig. 9e, f View Figure 9 ). Olixon has a similar structure on the third maxillary palpomere ( Fig. 9d View Figure 9 ) that has also been interpreted as a novelty for the genus by Guidotti (1999). The discovery of both apical bristles, i.e., one each on the second labial and the third maxillary palpomere ( Fig. 8b, c View Figure 8 ), in Cretolixon alatum , leads to the conclusion that both bristles were already present in the common ancestor of both groups. Thus, it is the reduction of one or the other of these bristles that adds to the morphological evidence for the monophyly of each subfamily, respectively. The innovation itself likely occurred earlier in the common ancestor ( Fig. 10 View Figure 10 ).
Krogmann et al. (2009) postulated that the single long bristle on the apex of the first flagellomeres of some Olixon species ( Fig. 3d View Figure 3 ) is homologous to one of those two apical bristles present in the recent macropterous genera ( Fig. 3a View Figure 3 ). For the first flagellomere, however, this line of arguments needs a slight modification. The single long bristle on the apex of flagellomere I of some Olixon species is most likely homologous to one of those two apical bristles present in the macropterous genera, and these again are most likely homologous to two of the six found in female Cretolixon ( Figs. 5b View Figure 5 , 6e View Figure 6 , 8a View Figure 8 ).
Another important character of Cretolixon is the position of the hind wing cross vein cu-a ( Fig. 7 View Figure 7 ), which is, similarly to its position in recent genera, clearly basal to the branching of the veins M and Cu (similar to Fig. 9b, c View Figure 9 ). In Eorhopalosoma and most of the unpublished Burmese amber fossils of the family the cross vein cu-a is opposite or very near to the branching of the veins M and Cu (similar to Fig. 9a View Figure 9 ). Brothers (1975) and Brothers and Carpenter (1993) regarded the basal position of the cross vein cu-a as the ancestral character state among aculeates and a distal position as the derived state but mentioned that several reversals back to the ancestral state occurred throughout the aculeates, and this might be true for Cretolixon and the recent rhopalosomatid genera as well.
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