Taxonomic revision of the Afrotropical Agabus raffrayi species group with the description of four new species (Coleoptera, Dytiscidae).

William F Englund,Johannes Bergsten,Olof Biström,Laban Njoroge,Kelly B Miller,David T Bilton

doi:10.3897/zookeys.963.53470

Abstract

We revise the Afrotropical Agabus raffrayi species group, motivated by the discovery of new diversity in Kenya and South Africa. Whilst Agabus is mainly a holarctic genus, the Agabus raffrayi group is restricted to high altitude regions of eastern Africa and temperate parts of South Africa, from where we describe the southernmost Agabus in the world. The following new species are introduced: Agabus anguluverpussp. nov. from Mount Kenya in central Kenya, Agabus austellussp. nov. a widespread species in South Africa, Agabus riberaesp. nov. from the Kamiesberg and northeastern Cederberg ranges in the Northern and Western Cape Provinces of South Africa and Agabus agulhassp. nov. from the Agulhas Plain, Western Cape Province, South Africa. We provide a distribution map, a determination key for males, quantitative measurements of diagnostic characters, habitus photos and detailed photos of male genitalia for all described species in the group, as well as images of diagnostic characters and habitats. The presence or absence of an elongated section between the subapical broadening and the base of the apical and subapical teeth of the male aedeagus is a useful novel character, first revealed by our study. In contrast with the most recent revision of Afrotropical Agabus, we show that Agabus ruwenzoricus Guignot, 1936 is restricted to eastern Africa; South African records of this species having been based on misidentifications, no species of the group being common to southern and eastern Africa. We speculate that the raffrayi group may display phylogenetic niche conservatism, being restricted, as an originally temperate taxon, to higher elevations in tropical eastern Africa, but occurring at lower altitudes in temperate South Africa.

Highlights

With over 170 species, Agabus Leach, 1817 is a large and complex genus of diving beetles which is diverse in temperate regions of the Holarctic
In contrast with the most recent revision of Afrotropical Agabus, we show that Agabus ruwenzoricus Guignot, 1936 is restricted to eastern Africa; South African records of this species having been based on misidentifications, no species of the group being common to southern and eastern Africa
At present this group consists of five species: A. dytiscoides Régimbart, 1908, A. pallidus Omer-Cooper, 1931, A. raffrayi Sharp, 1882, A. ruwenzoricus Guignot, 1936 and A. sjostedti Régimbart, 1908

Summary

Introduction

With over 170 species, Agabus Leach, 1817 is a large and complex genus of diving beetles which is diverse in temperate regions of the Holarctic. African tropico-alpine ecosystems are believed to be relatively young (Linder 2014) and Nilsson (1992a) suggested that the cold, dry climate of the Quaternary may have forced Afrotropical Agabus to adapt to higher altitudes in order to survive, and that this adaptation cannot be reversed Species of this largely temperate genus may display a degree of phylogenetic niche conservatism (sensu Morinière et al 2016), physiologically restricting them to relatively cool climates. Such suggestions correlate with the apparent lack of high-altitude specialist Agabus in South Africa, an area that has retained a relatively temperate climate throughout the Quaternary period, in the Cape (Meadows and Baxter 1999; Dupont et al 2011)

Material and methods

Discussion