Male genitalia of Exeretonevra Macquart (Diptera: Xylophagidae): Structure, function and phylogenetic implications

AbstractThe search for phylogenetically informative, adult morphological characters to clarify the relationships of the xylophagid genus Exeretonevra with other members of the lower Brachycera has yielded few synapomorphies. In this study, the male genital musculature of Exeretonevra angustifrons Hardy is examined and compared with other members of the lower Brachycera to ascertain whether this data set can support the inclusion of Exeretonevra in the infraorder Xylophagomorpha. Most genitalic muscle complexes of Exeretonevra conform to the plesiomorphic brachyceran configuration, with those of the cerci, epandrium and hypandrium possessing some apomorphic features. Although larval morphology and molecular evidence conclusively place Exeretonevra in the Xylophagidae, the male genital musculature suggest an affinity with the superfamily Asiloidea (infraorder Muscomorpha). In particular, Exeretonevra is the only taxon outside the infraorder Muscomorpha with a third tergosternal muscle bundle M53 present. No synapomorphies of genital musculature support the inclusion of Exeretonevra within the Nemestrinidae, a placement that has been supported by previous authors. We show that changes in the plane of movement of sclerotised structures may be correlated with changes in muscle attachments. Phylogenetic conservatism and extensive homoplasy are features of the male genitalic musculature of lower Brachycera and Exeretonevra is no exception.