Abstract:
We investigate how late Cenozoic orogenics and climatic change might have influenced the history of
taxon diversification and current species ranges in an endemic, Afrotropical, insect genus. Diastellopalpus
van Lansberge is a near basally-derived taxon in the dung beetle tribe Onthophagini (Coleoptera:
Scarabaeidae: Scarabaeinae) that has diversified into 32 known species primarily centred on intertropical
forests. Basal dichotomies in both published (Josso & Prévost, 2000) and re-analyzed phylogenies divide
the species into clades that are geographically centred either to the east or west of the eastern highlands that
underwent uplift from the Miocene (16 MY). There is broad climatic overlap between many of the species
but clear separation along a minimum spanning tree in ordinal space where they are divided into taxa with
either lowland or highland centres of distribution. Observed spatial distributions of six defined species
groups (A-F) (Wide:- B: equatorial west to east; D and E: west to central; F: intertropical, west to
southeast; Restricted:- A: southeast; C: central) mostly differ from predicted climatic ranges, presumably,
due to historical constraints on species dispersal. A trend from dominance of montane or wet lowland forest
associations in species of more basally derived lineages (groups A-C) to dominance of drier upland forest
and moist woodland associations in species of more terminally derived lineages (groups D-F) is, perhaps,
linked to the stepped trend to cooler, dryer climate in the late Cenozoic.
