Historical biogeography of the cicadas of Wallacea, new Guinea and the West Pacific: a geotectonic explanation
Abstract The present-day distribution patterns of the cicadas of Wallacea, New Guinea, and the West Pacific reflect the extremely complex geotectonic history of that area. The patterns found in two unrelated monophyletic groups of cicadas (Insecta, Homoptera, Cicadoidea), the subtribe Cosmopsaltriaria and the tribe Chlorocystini with its sister tribe Prasiini, are analysed and related to data from the geological literature. The two groups have a comparable distributional range over Sulawesi, Maluku, New Guinea, the Bismarck Archipelago, and the East-Melanesian archipelagos, to Tonga and Samoa. The occurrence of endemic species, species groups, and genera in congruently delimited parts of this range made us recognize 14 areas of endemism. The areas of endemism coincide with geological entities, which have been isolated during a considerable period of time. Most of the areas originated from oceanic island arcs, which developed as a result of subduction along the southern and western edges of the Pacific tectonic plate, others are rifted microcontinents. Concentrations of species and especially endemic species of the various cicada genera in different areas of endemism suggest that each of these genera evolved in isolation on one of the afore mentioned geological entities. These entities can therefore be regarded as source areas for the genera. The island arc fragmented as a result of collisions first with the Asian- and later with the Australian tectonic plate and several of its parts reamalgamated at the northern craton of the Australian plate, where they now form the greater part of the island of New Guinea. After reamalgamation of the arc fragments the cicadas of the respective genera that had evolved on these fragments could disperse into adjoining areas, but since cicadas are poor dispersers the source areas of the genera can still be recognized in present-day distribution patterns. The generic relationships in the two groups of cicadas under study indicate area relationships that comply with the latest palaeogeographic reconstructions. The main vicariant speciation events in the cicada cladograms correspond with the presumed sequences of fragmentation of the island arc. Cicada phylogeny and distribution combined reflect the historic area relationships rather than the present ones.