Ancient polymorphism, secondary contact, taxonomic inflation or all of them together? Mito-nuclear discordance in the Angolan girdled lizard (Cordylidae: Cordylus), with the description of a new species from the central highlands

Species delimitation and the process of speciation are central themes in evolutionary biology and taxonomy. Modern molecular techniques have challenged the dogmatic assumption that speciation represents a simple bifurcating process, revealing complex evolutionary dynamics, such as incomplete lineage sorting and reticulated speciation. The diverse topography of Angola, which includes coastal savannahs and high-elevation grasslands, fosters intricate evolutionary processes across a broad range of faunal taxa. Recent studies on Angolan species, such as Cordylus or Afroedura lizards, have provided evidence for these complex patterns of diversification and introgression between populations from different regions. We investigate these processes by revisiting the Angolan Cordylus to gain a better understanding of their diversity, biogeographical patterns, and the evolutionary forces driving their speciation. To investigate this, we conducted a broad geographical survey and performed a detailed examination of molecular and morphological (both internal and external) data. Our results necessitate the description of a new species from the central highlands, Cordylus cultratus sp. nov., and have identified mito-nuclear discordance, which challenges the taxonomic stability of the Cordylus machadoi group. However, this inconsistency might be explained by incomplete lineage sorting, introgression, and/or taxonomic inflation, thus hindering any taxonomic actions within this group.