Speciation, faunal affinities and geographical dispersal of black flies (Diptera: Simuliidae) in the Oriental Region.

The simuliid fauna of the Oriental Region is reviewed in comparison with those in five other zoogeographical regions. It is relatively young, represented by only one genus Simulium, which is regarded as the most specialized among 26 genera of the family Simuliidae. The Oriental Region has the second largest simuliid fauna with 524 species or 23.8% of the world total of 2204 extant species. This species richness is associated with a high speciation index (15.4), reflected especially by the high speciation rates of two dominant subgenera Gomphostilbia and Simulium although the number of lineages in the Oriental Region is moderate (34 or 20.6% of the total 165). The Oriental fauna has relationships with all other zoogeographical regions at the lineage level, having the highest affinity index (31.9) with the Palearctic Region. It is inferred that eight of 10 Oriental subgenera moved during the ice ages from the Palaearctic to the Oriental Regions; the subgenus Gomphostilbia evolved into 11 species-groups and underwent species radiation in the Oriental Region. On the other hand, two other subgenera, Nevermannia and Simulium, moved southward during the ice ages after evolving into species-groups. In the post-ice ages, most lineages retreated northward, with different portions of species left in the Oriental Region, although some lineages failed to retreat and survived as relict lineages in the Oriental Region.