Out of the Palaearctic: the Helophorus water beetles of the Afrotropical Region (Coleoptera: Helophoridae)

Abstract

Helophorus Fabricius, 1775 (Coleoptera: Hydrophiloidea: Helophoridae) is an old and largely Holarctic genus of beetles, with most extant diversity concentrated in the Palae­arctic. As with a number of primarily northern temperate lineages, the genus has colonised the Afrotropical Region, with species described from the Ethiopian Highlands and southern Africa. Here, the Afrotropical Helophorus fauna is revised, based on a study of all primary types and additional material, including extensive recent collections from South Africa. The known Afrotropical fauna is shown to be comprised of six species, only three of which were previously described: H. aethiopicus Régimbart, 1907, from southern highland areas of Ethiopia, H. aethiops J. Balfour-Browne, 1954 known from summer and year-round rainfall areas of South Africa and Namibia and H. cooperi Orchymont, 1948, stat. nov., described as a subspecies of H. aethiopicus and still only known from the type locality in Ethiopia. To these, three new species are added: H. brumopluvialis sp. nov., widespread in winter rainfall areas of the Western and Northern Cape Provinces of South Africa, H. nyandaruaensis sp. nov. from mountains of the East African Rift in Kenya and H. simiensis sp. nov. from the Simien Mountains of northern Ethiopia. All species are (re)described in detail and illustrated with high-resolution photos. Known distributions are mapped and a key to species provided. It is suggested that the two South African species may have speciated allochronically, due to seasonal shifts in life cycle associated with the development of the winter rainfall regime in the Cape during the Plio-Pleistocene. Helophorus are hypothesised to have colonised the Afrotropics on at least two occasions from separate Palaearctic ancestors.