Demography
The lower degree of genetic variation in the EF-1ɣ region is expected due to this being a nuclear gene and having a lower mutational rate than the two mitochondrial genes . The high haplotype diversity across the various species and gene regions indicates that enough time has elapsed for diversification to occur. Majority of the species display high haplotype diversity and low nucleotide diversity across the gene regions (except for S. unispinosus which does not have a high haplotype diversity). This trend is indicative of a rapid expansion from a relatively small population . In order to gain further insight into the demographic history of these species for which only a few specimens were available, more samples are required. The incongruence of the placement of S. venterstadensis in the haplotype network of CO1 is potentially due to mitochondrial introgression from an ancient admixture between the two species (Croucher et al., 2004; Horoiwa et al., 2021; Kornilios et al., 2016). This could explain why the same pattern is not observed in the other gene regions, but a larger sample size of S. venterstadensis is required to fully explore this possibility.
The EF-1ɣ results for S. maraisi indicate that the population has undergone a recent expansion event based on the negative Tajima’s D and Fu and Li’s D as well as the shape of the haplotype network This expansion based on the dated phylogeny likely occurred in the mid-Miocene, coinciding with the formation of the Benguela current, leading to the Karoo experiencing a more tropical climate . This may have given males, which are vulnerable to desiccation, more favourable conditions to disperse further than is usually possible under arid conditions. This could have contributed to the wide species range ofS. maraisi seen today. The influence of the Benguela current formation on accelerated speciation has previously been recorded in southern Africa. In Namibia and the Northern Cape, the formation of the Benguela current led to xeric conditions which caused local speciation events such as the formation of the aeolian sand dune system in Namibia, which in turn influenced the speciation of the Pachysoma dung beetles as well as Senecio genus of daisies . The influence of this current on the succulent Karoo and Fynbos biomes are also well linked to speciation, such as on the tent tortoise, Psammobates tentorius as well as numerous plant species . The effect of the Benguela on the Nama Karoo fauna, where S. maraisi is found is however largely unexplored, and requires further research.