Phylogeography of the House Bunting complex: discordance between species limits and genetic markers

Abstract

Emberiza striolata has traditionally been viewed as a single polytypic species, but recent taxonomic reviews of its morphology, vocalizations and genetic data have led to the recommendation that two species be recognized within this complex, the House Bunting Emberiza sahari in the west, and the Striolated Bunting Emberiza striolata (including the subspecies Emberiza striolata saturiator and Emberiza striolata ‘jebelmarrae’) in the east of the range. However, reportedly intermediate birds have been described from northern Darfur, Sudan, and the Ennedi Massif, northeast Chad, bringing the two-species hypothesis into question. Here, we attempt a more comprehensive geographic sampling of all taxa of E. sahari and E. striolata, and we report the results of an examination of purported intermediate specimens, as well as the re-examination of the long type series of the controversial taxon Emberiza striolata ‘jebelmarrae’ described from western Sudan. Our results confirm a marked east–west divergence in the House Bunting complex based on two mitochondrial DNA (mtDNA) markers, but surprisingly reveal that samples of E. striolata ‘jebelmarrae’ cluster with the western clade, whereas their morphology is clearly allied with that of other populations in the eastern clade. However, our analysis suggests that all of the specimens believed to be intermediate in morphology can be categorically placed with other examples of the western clade (E. sahari). At present, it is impossible to definitively explain the phylogenetic position of E. striolata ‘jebelmarrae’, but we hypothesize that the paraphyly in mtDNA is the result of introgression during the initial phase of secondary contact, and does not impinge on the decision to recognize two species. Complex spatio-temporal population patterns caused by late Pleistocene climate changes might have led to multiple secondary contact events between the eastern and western clades.