How many species of angulate tortoises occur in Southern Africa? (Testudines: Testudinidae: Chersina)

Abstract

Using range‐wide sampling and 1,143 bp of mtDNA (cytochrome b gene) and 14 microsatellite loci, we examined genetic differentiation in the widely distributed Southern African angulate tortoise (Chersina angulata). We found evidence for two genealogical lineages that differ in both genetic marker systems and their preferred habitat conditions. According to a fossil‐calibrated molecular clock for all African tortoise lineages using 1,870 bp mitochondrial and 1,416 bp nuclear DNA, the two lineages of C. angulata diverged in the Pliocene (approx. 3.8 million years ago). Species distribution models reveal that the ranges of the two lineages shifted little since the Last Glacial Maximum, which is in agreement with the demographic population descriptors suggestive of stationary populations that did not experience expansion. One lineage occurs in the west, and the other in the south of the extant distribution range. In the geographic contact zone, the two lineages hybridize extensively, providing evidence for their conspecificity under the biological species concept. Each lineage could be recognized as a distinct subspecies, but the ill‐defined geographic origins of the type material of the available names prevent their identification with any taxon. With respect to the nuclear genomic markers, the western lineage shows further north‐south substructuring. A few genetically mismatched tortoises are interpreted as human translocations. Our study underlines that confiscated or captive angulate tortoises of unknown geographic provenance should not be released without prior genetic screening to avoid genetic pollution of wild populations.

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

“…However, the insular population was not genetically differentiated from the western mainland lineage. In contrast to the deep divergences estimated by Daniels et al (2007), Spitzweg et al (2020) inferred that the two lineages of C. angulata diverged only in the Pliocene (approx. 3.8 million years ago).…”

“…The phylogeography of Homopus areolatus was studied by Hofmeyr et al (2020) based on range-wide sampling and a 680-bp-long fragment of the mitochondrial ND4 gene combined with evidence from species distribution modeling. Similar to Chersina angulata (Daniels et al 2007;Spitzweg et al 2020) and Pelomedusa galeata (Vamberger et al 2018), two clades were identified, one from the west and the other from the south and east of the range. For the two tortoise species, a small over-lap zone between the clades has been identified (Fig.…”

“…Other important aspects of this study relate to the speckled color pattern characteristic for the formerly recognized subspecies C. s. cafer and this was suggested to be a result of adaptation to the local rock type (granite-gneiss). Daniels et al (2007) and Spitzweg et al (2020) have examined phylogeographic structuring in Chersina angulata. Based on sequence variation of three mtDNA fragments (COI: 599 bp, cyt b: 320 bp, ND4: 791 bp), Daniels et al (2007) inferred the existence of three mitochondrial clades in the northwestern, southwestern, and southern part of the South African Cape region that corresponded to two more inclusive clades (western Cape vs. southern Cape), with divergence time estimates for the three clades ranging from 8.4 to 10.4 million years.…”

“…Daniels et al (2007) suggested that the two more inclusive clades could represent distinct species. Spitzweg et al (2020) re-examined the phylogeography of C. angulata using range-wide sampling and combined evidence from cyt b sequences (1,143 bp), 14 microsatellite loci and species distribution models. For a fossil-calibrated molecular clock calculation using 1,870 bp mtDNA and 1,416 bp nDNA, these authors selected representative samples of C. angulata and all other African tortoise lineages.…”

“…Microsatellite analyses indicated broad admixture in the geographic contact zone of the two lineages and supported that they are conspecific under the Biological Species Concept (Mayr 1942). Spitzweg et al (2020) concluded that each of the two genealogical lineages could be identified with a particular subspecies, but the unclear taxonomic identity of the type specimens of the available early 19 th century names prevented their naming. This situation might be clarified using aDNA approaches to characterize the type material genetically.…”