Gone with the wind: westward dispersal across the Indian Ocean and island speciation in Hemicordulia dragonflies (Odonata: Corduliidae)

Abstract

The taxonomy and biogeography of the western representatives of the largely Papuan-Australian genus Hemicordulia are discussed and compared with other alate fauna including butterflies, birds, bats and other dragonflies. Specimens from Malawi, Mozambique, Réunion, South Africa, Tanzania and Uganda were compared with Indian specimens of H. asiatica, with which they were previously regarded conspecific. They are found to be distinct and are described as the continental H. africana n. sp. and those from Réunion as H. atrovirens n. sp. The three species were compared with H. similis of Madagascar and H. virens of Mauritius. Insufficient material of the Seychelles taxon H. similis delicata was available; it may represent another insular endemic species. The distribution of Hemicordulia is discussed in the light of the dispersal capacity of Odonata and the biogeography of taxa with similar distributions in the region, with an emphasis on the survival of ‘oceanic’ species on the continent. Recent (i.e. in the last few million years) trans-oceanic airborne dispersal aided by westward storms, is the most likely explanation for the distribution of the genus in Africa and the Indian Ocean islands, as well as for other winged animals of Asian affinities in the region. The world range of Hemicordulia is largely insular, broadly excluding continents, and H. africana n. sp. demonstrates ‘inverted insularity’: all continental sites are in proximity to large water bodies, such as the great African lakes. This pattern may be related to the climatological instability of these sites, which offer suitable cool habitat where competition is (temporarily) reduced. Hemicordulia prefer cool conditions, but may be vulnerable to overheating and competition with more warm-adapted species.