Lifting the blue-headed veil – integrative taxonomy of the Acanthocercus atricollis species complex (Squamata: Agamidae)

We present the first integrative review of the African agamid lizard Acanthocercus atricollis, a broadly distributed species found from Ethiopia through East Africa to Angola and South Africa. Since the original description of the species approximately 170 years ago six subspecies have been described, mainly on the basis of coloration characters. Our study presents new morphological and genetic data, which together suggest that A. atricollis is a complex of multiple species. External morphological characters and cranial osteology support some of the taxonomic differentiation implied by coloration. We also provide complementary 16S rRNA mitochondrial DNA (mtDNA) sequence data analysed in the context of species delimitation. Our integrated data support several systematic and taxonomic changes, including (1) Acanthocercus branchi is part of the A. atricollis complex, (2) the subspecies A. gregorii, A. minutus, A. ugandaensis, and A. kiwuensis merit species rank, (3) A. atricollis loveridgei is a synonym of A. a. gregorii, (4) Agama cyanocephalus, a former synonym of A. atricollis, is now recognized as full species distributed in Angola, Zambia and extreme northern Namibia. The distribution and diversity of the A. atricollis species complex supports the presence of a biogeographic arid corridor connecting eastern and southern Africa.