The thoracic anatomy of the swift lousefly Crataerina pallida (Diptera)—functional implications and character evolution in Hippoboscoidea

The thoracic skeletomuscular system of the swift lousefly Crataerina pallida (Diptera: Hippoboscidae) is documented with scanning electron microscopy, micro-computed tomography and three-dimensional reconstruction. The morphological results are discussed with respect to ectoparasitism and flightlessness. The evolution of thoracic characters in Hippoboscoidea is reconstructed based on a parsimony analysis of 44 thoracic characters. The results confirm the monophyly of Hippoboscoidea, Pupipara (Hippoboscidae + Streblidae + Nycteribiidae) and the bat flies (Streblidae + Nycteribiidae). The monophyletic origin of Hippoboscidae is challenged with respect to the genus Ornithoica, which displays several plesiomorphic features compared with conditions shared by the remaining Pupipara. The thorax of the species in the three families is distinctly affected by the ectoparasitic lifestyle. The dorsal segmental borders are obliterated, and the thorax is usually strongly flattened. The legs are adapted to cling to the host and to move efficiently in the fur or plumage. A heel-like claw tooth supports large claws. Different patterns of reduction of the flight apparatus occur in the group. Even though Crataerina and Stenepteryx are close relatives and similar in their general thoracic configuration, differences in the muscular patterning suggest independent losses of the capacity for flight.