Cladistic, phenetic and biogeographical analysis of the flightless dung beetle genus, Gyronotus van Lansberge (Scarabaeidae: Scarabaeinae), in threatened eastern Afrotropical forests

Abstract

By virtue of their low vagility, flightless insects are useful indicators of biogeographical history. Relationships of the flightless dung beetle genus, Gyronotus, are of particular interest due to its Gondwanaland ancestry, distinctive relict distribution along the south-eastern seaboard of Africa, and its restriction to forests which are seriously threatened by exploitation. Because of the limited number of diagnostic morphological characters, it was necessary to code morphometric data in order to conduct distance and cladistic parsimony analysis of interspecific relationships in Gyronotus. There was a good correlation between relationships indicated by the dendrograms/cladograms and those determined by an examination of aedeagus character states both of which indicate a disjunction between south and east African species and a broad separation between northern and southern South African species. Comparison of the bilaterally asymmetrical aedeagi of Gyronotus with the symmetrical aedeagi of the sister genus, Anachalcos Hope, suggests geographical polarization of character states from greater plesiomorphy in east African Gyronotus to greater apomorphy in South African species, particularly in the southernmost element in which the aedeagus shows extreme asymmetry. Furthermore, body shape follows a similar geographical gradient in that the three Gyronotus species of tropical east Africa are significantly more elongate than the three ovoid, lowland/afromontane species of South Africa. An examination of historical factors suggests that this spatially-restricted distribution is the relict of a very old tropical lowland pattern. In extant taxa, the phylogenetic polarization is towards one of five main centres of afrotropical forest biodiversity in the geologically old Eastern Arc and the adjoining lowland forest (Swahili centre of endemism). Survivors from old lineages may be one reason for such centres of high biodiversity.