Chromosome analyses challenge the taxonomic position of Augosoma centaurus Fabricius, 1775 (Coleoptera: Scarabaeidae: Dynastinae) and the separation of Dynastini and Oryctini

Augosoma centaurus Fabricius, 1775 (Melolonthidae: Dynastinae), one of the largest Scarabaeoid beetles of the Ethiopian Region, is classified in the tribe Dynastini MacLeay, 1819, principally on the basis of morphological characters of the male: large frontal and pronotal horns, and enlargement of fore legs. With the exception of A. centaurus, the 62 species of this tribe belong to ten genera grouped in Oriental plus Australasian and Neotropical regions. We performed cytogenetic studies of A. centaurus and several Asian and Neotropical species of Dynastini, in addition to species belonging to other sub-families of Melolonthidae Leach, 1819 and various tribes of Dynastinae MacLeay, 1819: Oryctini Mulsant, 1842, Phileurini Burmeister, 1842, Pentodontini Mulsant, 1842 and Cyclocephalini Laporte de Castelnau, 1840. The karyotypes of most species were fairly alike, composed of 20 chromosomes, including 18 meta- or sub-metacentric autosomes, one acrocentric or sub-metacentric X-chromosome, and one punctiform Y-chromosome, as that of their presumed common ancestor. Among the Dynastinae we studied, the karyotypes of the two species of Oryctes Illiger, 1798 and A. centaurus deeply differ from others: they look alike and are composed of 18 chromosomes only, many acrocentric autosomes and neo-sex chromosomes resulting from an X-Y-autosome translocation. The reassessment of their morphologies, in particular of female specimens, exhibits many shared characters. The genetic proximity of Augosoma and Oryctes is confirmed by the comparison of DNA sequence data separately found in the literature. Thus, the genera Augosoma and Oryctes should be grouped together, and not split into two different tribes. These results challenge the separation of the tribes Dynastini and Oryctini and the traditional use male exaggerated characters for establishing a systematic classification.