Systematics of the endemic south-west African dung beetle genus Pachysoma Macleay (Scarabaedae: Scarabaeinae

Abstract

The phylogenetic validity of Pachysoma Macleay, 1821, is assessed. Cladistic analysis of 64 adult characters from 37 taxa comprising all Scarabaeini genera (except the monotypic Madateuchus Paulian, 1953) and two outgroup Canthonini genera, resulted in some currently recognised genera (i.e. Sceliages Westwood, 1837; Kheper Janssens, 1940; and Drepanopodus Janssens, 1940) being recognised as paraphyletic. Pachysoma comprises a monophyletic clade of highly derived Scarabaeus Linnaeus, 1758. To further nomenclatural stability within the Scarabaeini, Pachysoma should best be considered a subgenus of an expanded genus Scarabaeus. Neopachysoma Ferreira, 1953; Mnematium Macleay, 1821 and Neomnematium Janssens, 1938 are maintained as synonyms of Scarabaeus s.l. The unique biology of Pachysoma is interpreted as an adaptation to arid conditions, and is presumably derived from ball rolling and wet dung feeding. Aridification of the Namib Desert is postulated to have initiated the evolution of Pachysoma from a Scarabaeus-like ancestor, while dune movement accounts for their current distribution. The evolutionary history of Pachysoma is discussed based on the phylogenetic analysis, and distributional and biological information. The subgenus Scarabaeus (Pachysoma) Macleay, 1821 is revised. All thirteen species of the subgenus are endemic to the west coast of southern Africa. A key to all S. (Pachysoma) species is provided, and their distributions are mapped. Two new species Scarabaeus (Pachysoma) endroedyi and Scarabaeus (Pachysoma) glentoni from the southwestern Cape are described. The subspecies S. (P.) denticollis penrithae (Zunino) is synonymised with S. (P.) denticol/is denticollis (Peringuey). The synonymy of S. (P.) hessei (Ferreira) with S. (P.) hippocrates (Macleay) is confirmed. S. (P.) valef/orae (Ferreira) previously considered a synonym of S. (P.) schinzi (Fairmaire) is reinstated as a valid species. The missing type series of Pachysoma hessei Ferreira is traced. A lectotype is designated for Scarabaeus aesculapius Olivier, three paralectotypes are designated for Pachysoma marginatus Peringuey and one paralectotype for Pachysoma denticolle Peringuey. Notes on the type series, distribution records, morphological variation and known biology, are provided for all flightless Scarabaeini. A checklist of all valid species and their synonyms of Pachysoma, Neopachysoma, Mnematium and Neomnematium is included. KEYWORDS FOR THESIS RETRIEVAL: Insects, Coleoptera, Scarabaeidae, Scarabaeinae, Scarabaeini, Afrotropical, Pachysoma, Neopachysoma, Mnematium, Neomenmatium, Scarabaeus, Kheper, Sceliages, Drepanopodus, Pachylomerus, cladistic, phylogeny, endemic, dung beetles, flightless, food preference, dry dung, detritus, psammophily, relocation strategy, systematic revision, biology, distribution.