Fly on the wall: Evolution of Attachment Devices in Lower Diptera

Diptera display a broad array of adhesive devices occurring on different parts of the legs. Characters of the distal leg region of 32 species and 10 outgroups were mapped onto the phylogeny of Wiegmann et al. (2011) to evaluate the evolution of attachment structures in Diptera. Smooth and hairy attachment structures are present in Diptera. A smooth arolium is present in Tipulomorpha but missing in the remaining dipterans. It has very likely evolved independently from the arolia of the outgroups; though a possible re-evolution is discussed as well. Hairy empodia are a groundplan feature of Diptera; but missing in several genera. Hairy pulvilli can be found in most subgroups. However; two species evolved smooth pulvilli. Very often both pulvilli and empodia are present. The size and shape of these two structures is very variable. The shape of the tips of tenent hairs differs considerably between the different groups. The potential to modify pretarsal attachment devices in their structural details has probably contributed to the very successful diversification of Diptera.