Abdominal serial homologues of wings in Paleozoic insects

The Late Paleozoic acquisition of wings in insects represents one of the key steps in arthropod evolution. While the origin of wings has been a contentious matter for nearly two centuries, recent evolutionary developmental studies suggest either the participation of both tergal and pleural tissues in the formation of wings(1) or wings originated from exites of the most proximal leg podite incorporated into the insect body wall.(2) The so-called dual hypothesis'' for wing origins finds support from studies of embryology, evo-devo, and genomics, although the degree of the presumed contribution from tergal and pleural tissues differ.(3-6) Ohde et al.,(7) confirmed amajor role for tergal tissue in the formation of the cricket wing and suggested that wings evolved from the pre-existing lateral terga of a wingless insect ancestor.'' Additional work has focused on identifying partial serially homologous structures of wings on the prothorax(8,9) and abdominal segments.(10) Thus, several studies have suggested that the prothoracic horns in scarab beetles,(9) gin traps of tenebrionid and scarab beetle pupae,(11,12) or abdominal tracheal gills of mayfly larvae(1,13) evolved from serial homologues of wings. Here, we present critical information from abdominal lateral outgrowths (flaps) of Paleozoic palaeodictyopteran larvae, which show comparable structure to thoracic wings, consisting of cordate lateral outgrowths antero-basally hinged by muscle attachments. These flaps therefore most likely represent wing serial homologues. The presence of these paired outgrowths on abdominal segments I-IX in early diverging Pterygota likely corresponds to crustacean epipods(14,15) and resembles a hypothesized ancestral body plan of a protopterygote'' model.

Automated summary

The acquisition of wings in insects during the Late Paleozoic period is a significant step in the evolution of arthropods. Recent studies have suggested two possible origins of wings: the involvement of both tergal and pleural tissues or the incorporation of exites from the proximal leg podite into the insect body wall. The "dual hypothesis" for wing origins is supported by embryology, evolutionary developmental biology, and genomics research. These studies have also found potential homologous structures of wings in other body parts, such as the prothoracic horns in scarab beetles, the gin traps of tenebrionid and scarab beetle pupae, and the abdominal tracheal gills of mayfly larvae.