The taxonomy, systematics and biogeography of the austral horse fly tribe scionini (Diptera : Tabanidae)
The Tabanidae are a large cosmopolitan family of medically and ecologically important Diptera. Adults of both sexes are important pollinators, and the females are known to mechanically transmit multiple disease agents while blood-feeding, affecting humans and animals. The tribe Scionini of the subfamily Pangoniinae consists of stoutly built and hairy-eyed flies predominantly austral in distribution, occurring in Australia, New Guinea, New Zealand and South America. The Scionini are divided into six recognised genera; Caenopangonia Krober, 1930, Fidena Walker, 1850, Goniops Aldrich, 1892, Pityocera Giglio-Tos, 1896, Scione Walker, 1850, and the widest distributed genus Scaptia Walker, 1850. Scaptia is further divided into seven subgenera; Lepmia Fairchild, 1969, Pseudomelpia Enderlein, 1922, Myioscaptia Mackerras, 1955, Palimmecomyia Taylor, 1917, Plinthina Walker, 1850, Scaptia Walker, 1850, and Pseudoscione Lutz, 1918. The taxonomy of the Scionini has not been revised in over 50 years. Consequently, new material has accumulated in museums corresponding to 18 new species of Scaptia (Plinthina) (5 spp.n.), Scaptia (Pseudoscione) (7 spp.n.), Scaptia (Scaptia) (1 sp.n.), Scaptia (Myioscaptia) (2 spp.n.), and the novel genus Anzomyia Lessard, gen.n. (3 spp.n.), all of which have been described and illustrated herein. Molecular data was employed to provide the first quantitative phylogenetic hypothesis for the Scionini, including the systematic placement of all the tribes in the Pangoniinae. An alignment of six molecular markers, including mitochondrial (COI and COII), ribosomal (28S) and nuclear (AATS, CAD regions 1, 3 and 4) genes, 5757 bp in total, was analysed for 176 taxa using Bayesian and maximum likelihood approaches. Results indicated the Scionini are strongly monophyletic, excluding Caenopangonia and Goniops, which were subsequently removed from the Scionini and reassigned to the Pangoniinae tribes Mycteromyiini and Goniopsinini, Lessard tribe.n., respectively. The South American genera Fidena, Pityocera and Scione were strongly monophyletic, corresponding to current morphology-based classification schemes. Interestingly, Scaptia recovered as broadly paraphyletic, which was corrected by formally raising several subgenera to genus level (Lepmia, Myioscaptia, Palimmecomyia, Plinthina, Pseudomelpia and Pseudoscione), resurrecting previously synonymised genera (Apocampta Schiner, 1867, Copidapha Enderlein, 1922, Parosca Enderlein, 1922, Osca Walker, 1850, and Triclista Enderlein, 1922) and establishing a novel genus from New Zealand (Aotearomyia Lessard, gen.n.). These molecular results were combined with morphological evidence to revise the taxonomy of the entire Scionini, including the redescription of all genera and subgenera, in addition to the development of a novel diagnostic key to all seventeen recognised genera. Divergence time estimates based on the molecular data and the fossil record placed global biogeographic radiations of the Pangoniinae in a temporal context. Results indicated that the Scionini are a typical Gondwanan group and are most likely Australian in origin. Furthermore, the diversification and current biogeography of the tribe appears to be influenced by the ancient fragmentation of Gondwana, involving a complex process of both vicariance and long distance dispersal. Future studies will benefit from more extensive sampling of the South American genera, in particular Fidena, Pityocera and Scione, which require further taxonomic revision and updating of the diagnostic keys to species.
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