Supplementary Data and Files: Application of the General Lineage Concept to resolve species boundaries in African vipers (genus Bitis)

The historical application of the morphological species concept has led to taxonomic uncertainties within many taxonomic groups, including the African vipers of the genus Bitis. In particular, species boundaries amongst the small-bodied arid to semi-arid living species have become contentious under modern thinking. We assessed their species boundaries by combining Sanger sequencing data with genotyping-by-sequencing (GBS) and qualitatively reviewed the morphology used to define these species. Our findings support previous phylogenetic studies showing paraphyly of B. caudalis, but our improved geographic sampling revealed additional lineages. Bitis albanica is nested within B. rubida forming a single lineage, and their morphological features entirely overlap, except perhaps for some colouration variation. While B. inornata was recovered as monophyletic, it is only weakly divergent from the B. rubida/albanica lineage and is not supported as a separate species. Morphologically, B. inornata overlaps with B. albanica and B. rubida for all scale counts but lacks supraocular horns, but this trait is known to variable within viper species. These relationships are supported by both Sanger sequence and GBS datasets and show the need for a full taxonomic revision - particularly given the lack of defining morphological traits, and of clear geographic boundaries between the taxa.