Taxonomic inflation due to inadequate sampling: are girdled lizards (Cordylus minor species complex) from the Great Karoo one and the same?

Abstract

Abstract The Great Karoo and Namaqualand of South Africa are home to a species complex of morphologically conserved lizards that occur in allopatry (Karoo: Cordylus aridus, Cordylus cloetei, Cordylus minor; Namaqualand: Cordylus imkeae). However, there are negligible morphological differences and a lack of obvious physical or climatic barriers, particularly among the three Karoo species. We hypothesized that poor geographic coverage in previous studies and lack of an explicit species concept has caused taxonomic inflation. We therefore tested species boundaries by examining multiple criteria: multi-gene phylogenetics, niche distribution modelling and re-examination of diagnostic morphological features with a larger sample size. We found that C. aridus, C. cloetei and C. minor lack diagnosable differences for both genetics and morphology. Distribution modelling, ranging from present day to the last interglacial period, show connectivity has been maintained especially during cooler periods. Conversely, C. imkeae is morphologically diagnosable, genetically distinct and lacks connectivity with the other taxa. By evaluating multiple operational criteria, we conclude that the C. minor species complex comprises only two species, C. minor (with C. aridus and C. cloetei as junior synonyms) and C. imkeae, demonstrating that species defined from inadequate data and lack of an explicit species concept can lead to taxonomic inflation.