Phylogenetic assessment and historical biogeography of the Psammophis leightoni complex
Stable and accurate taxonomy remains a primary component of conservation. By overlooking taxonomic disorder, conservation management strategies may ineffectively distribute resources. The Psammophis leightoni species complex is one such example where taxonomic confusion may have an influence on the conservation of threatened species. Psammophis leightoni, P. namibensis and P. trinasalis were all elevated to specific rank on the basis of ecological differences largely attributed to where these taxa occur. A molecular revision of Psammophiinae highlighted that P. leightoni and P. namibensis show levels of intraspecific divergence; however, this was based on single representatives per putative species. Psammophis leightoni is currently considered Threatened and is listed as Vulnerable [B1ab(iii)], but the taxonomic uncertainty surrounding the P. leightoni complex influences how these taxa should be regarded in a conservation context. To remedy this, I aim to validate the taxonomic status of members of the P. leightoni complex using phylogenetic analyses and species distribution modelling (SDM) techniques. Maximum likelihood and Bayesian inference approaches were applied to ascertain the genetic relationships within the P. leightoni complex. Uncorrected p-distances were generated to assess the level of divergence between taxa of the P. leightoni complex relative to its African congeners. Furthermore, a General Mixed Yule Coalescent model and its Bayesian implementation were used as tree-based methods for species delimitation. Species distribution models were carried out using a maximum entropy approach that estimated the climate suitability for these putative taxa defining their distributions during the last glacial maximum, mid-Holocene and under current climatic conditions. The phylogenetic analyses recovered all individuals of the P. leightoni complex in a monophyletic clade. Furthermore, the study taxa show intraspecific level divergences between taxa of the P. leightoni complex and are suggested to collectively represent a single taxon based on the species delimitation analyses. Additionally, the species distribution models showed no difference between these taxa's spatial distribution suggesting that taxa of the P. leightoni complex are not ecologically distinct. Assuming the P. leightoni complex represents a single species, meeting the prerequisites of the unified general species concept, a taxonomic revision is necessary to assign the appropriate taxonomic rank. Both P. namibensis Broadley, 1975 and P. trinasalis Werner, 1902 should be considered synonyms of P. leightoni Boulenger, 1902. As a result, P. leightoni should be considered widespread and in need of a conservation reassessment, potentially removing its current threat status.