Intraspecific patterns of mitochondrial variation in natural population fragments of a localized desert dung beetle species, Pachysoma gariepinum (Coleoptera: Scarabaeidae)

Phylogenetic, population, and coalescent methods were used to examine the genetic structuring of Pachysoma gariepinum, a flightless dung beetle species endemic to the arid west coast of southern Africa that exhibits interrupted south to north morphological clinal variation along a distributional gradient. Mitochondrial cytochrome oxidase I sequence data of 67 individuals from 5 localities revealed the presence of 3 geographically distinct evolutionary lineages (with an overall nucleotide divergence of 5.7% and a per-locality divergence of 1.9–3.8%) which display significant levels of genetic structuring. The separation of the lineages was estimated to have occurred between 2.2 and 5.7 million years ago—which is the late Miocene, early Plio-Pleistocene era—possibly in response to the ebb and flow of the Orange and Holgat River systems as well as the interactions between the moving and stable sand dune systems. Moreover the species' current range appears to have been influenced by the formation of advective fog resulting in a constant source of water in an area with low precipitation thereby allowing for the beetles to radiate to areas that were previously inhospitable. Fu's F-statistics and population parameters based on recent mutations indicated that little to no recent population growth has occurred. This together with changing anthropogenic factors and the recovery of 3 geographically discrete management units, points to a need for census data in order to monitor and conserve the genetic diversity of this species.