A revision of Afrotropical Agabus Leach (Coleoptera, Dytiscidae), and the evolution of tropicoalpine super specialists

Abstract. The thirteen species of Agabus Leach, 1817, of the Afrotropical Region are revised and classified into four species groups: the dibasic ambulator -group endemic to Ethiopia, ragazzii -group with five species in Ethiopia, raffrayi -group with five species in East and South Africa, and A.discicollis Ancey, 1882, endemic to Ethiopia, is placed in the Nearctic cordatus -group. Agabus perssoni sp.n. and Agabus galamensis sp.n. are described from the highlands of Ethiopia. Agabus ruwenzoricus Guignot, 1936, stat.n. is given specific rank. Agabus ferrugatus Régimbart, 1905, is synonymized with Agabus ragazzii Régimbart, 1887, and Agabus limbicollis Régimbart, 1905, is synonymized with Agabus raffrayi Sharp, 1882, syn.n. Lectotypes are designated for the following nominal species: Agabus discicollis Ancey, 1882, Agabus raffrayi Sharp, 1882, Agabus limbicollis Régimbart, 1905, Agabus pallidus Omer-Cooper, 1931, Agabus ruwenzoricus Guignot, 1936, Agabus sjostedti Régimbart, 1908, Agabus dytiscoides Régimbart, 1908, Agabus ragazzii Régimbart, 1887, Agabus ferrugatus Régimbart, 1905, and Gaurodytes abessinicus Zimmermann, 1928. Reconstructed phylogenies are presented for the raffrayi -and ragazzii -groups. The following adaptations to tropicoalpine habitats are suggested: (1) body and especially pronotum narrow, (2) head broad anteriorly, (3) hindwing small, and (4) hind leg long and slender. Biogeography and evolution of the studied species are discussed. Four different invasions of Holarctic lineages to the East African mountains are suggested. Recurrent periods of cold and dry climate are considered the chief driving force in the evolution of high altitude super specialists.