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

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.

Phylogeny and phylogeography of chelonians from sub-Saharan Africa—A review of current knowledge in tribute to Margaretha D. Hofmeyr

“…While integration of different data types has been carried out for P. tentorius to assess species level diversity (Zhao et al 2021b), it is also imperative that a species delimitation approach within a full phylogenetic framework is applied (Reid and Carstens 2012;Carstens et al 2013) that includes congeners. For example, confusing taxonomy and lack of an explicit species concept had plagued taxonomic assessments of some reptiles in southern Africa, but teasing out species can be accomplished when a clear concept is circumscribed in advance, and a phylogenetic approach is used to assess species (e.g., Taft et al 2022;Tolley et al 2022aTolley et al , 2022b).…”

Phylogeographic breaks and how to find them: An empirical attempt at separating vicariance from isolation by distance in a lizard with restricted dispersal

“…This approach reduces the likelihood of detecting spurious phylogeographic breaks, as independent loci are not expected to support concordant breaks in the absence of barriers to gene flow (Avise & Ball, 1990;Kuo & Avise, 2005). However, populations evolving along a single geographical gradient (i.e., under IBD) might still be apparently divided into distinct lineages, for example in the presence of large sampling gaps (Schwartz & McKelvey, 2009;Tolley et al, 2022;Wiemers & Fiedler, 2007). In that context, it appears crucial to test explicitly whether apparent phylogeographic breaks (e.g., reciprocally monophyletic groups in phylogenetic trees) delimit vicariant units separated by barriers to gene flow or have been generated by alternative processes such as IBD.…”