Conservation of Circellium bacchus Fabricius (Coleoptera: Scarabaeidae) : genetic population structure and ecological preferences

Abstract

Mitochondrial DNA (mtDNA) analyses was used to determine population structure of a rare dung beetle, Circellium bacchus Fabricius (Coleoptera: Scarabaeidae). Polymerase Chain Reaction (PCR) amplified fragments were analysed for Restriction Fragment Length Polymorphisms (RFLPs ). A specific gene section, cytochrome oxidase subunit I and II (COI\COII), was targeted for the analyses. Sixty-two beetles were analysed from nine different localities throughout their present distribution in the south and eastern Cape Province. The RFLP analyses revealed 28 haplotypes. The majority of the haplotypes were unique, private and closely related; two haplotypes from adjacent populations were shared. The most significant finding of this study is the separation of C. bacchus maternal lineages into two distinct clades (separated by 4.74 % sequence divergence). The eastern clade consists of a single population at Addo Elephant National Park and the second, larger western clade is formed by the remaining populations in the western area of this species' distribution. The most striking barrier to gene flow between the two clades is the Afromontane forest at Knysna presumed to have separated the clades during the late Pleistocene with the expansion of the westerly air currents over the southern tip of Africa. Ensuing expansion and retraction of the forest habitat during cyclical glacial and interglacial periods is proposed to have lead to fynbos fragmentation and the subsequent shallower phylogenetic structure within the western clade as no conspicuous zoogeographic barriers are currently present between the different populations. In conjunction with the molecular analyses ecological factors were also considered mainly to establish C. bacchus ' habitat specificity. It was found that C. bacchus density was highest in natural, undisturbed vegetation in both Addo Elephant National Park and Buffalo Valley Game Farm. Furthermore, dung preference for feeding and breeding purposes was determined by providing dung of buffalo, elephant, rhinoceros and cattle under controlled conditions. As there was no consistent pattern of preference for a specific dung type for feeding it was concluded that C. bacchus is a generalist in terms of feeding. However, the dung preference study for breeding clearly showed that C. bacchus preferred the moist and pliable dung textures of cattle and buffalo dung. A survey of the species that co-occur with C. bacchus was also conducted at both sampling localities (Addo Elephant National Park and Buffalo Valley Game Farm) and showed that there were no other dung beetle species that can apparently effectively compete with C. bacchus. The most important consideration in the conservation of C. bacchus is the distinctness of the two clades. These two clades should be regarded as separate Management Units (MUs) and translocations between the areas in which they occur should not be considered an option to increase viable population sizes outside of the areas represented by the two clades. Addo Elephant National Park and the De Hoop Nature Reserve are the only official nature conservation areas in which extant populations of C. bacchus are presently found. It is therefore essential that the co-operation of the local farm owners be obtained in conservation actions to ensure the survival of this enigmatic dung beetle.