Introduction
The Karoo region of South Africa has long been neglected in studies due to the assumption of low biodiversity in semi-arid regions . This began to change in 2015 when a Strategic Environmental Assessment (SEA) was undertaken to produce a report on the state of biodiversity in the region to assist governmental policy-makers in making informed decisions about land use change in the area through the Karoo BioGaps project . This became imperative as in previous years pressure for land use change increased due to economic incentives such as mining, farming, renewable energy, intensive shale gas exploration and the Square Kilometre Array (SKA) . To date there is still however, few studies on the faunal diversity in the area .
The Karoo region of South Africa has a geologically rich history. The Karoo basin of South Africa in combination with four other basins globally form the Gondwanan foreland basins which were formed by collisions and terrain accretion tectonics along Gondwana’s southern edge . The Karoo basin sedimentation dates from the late Carboniferous to the middle Jurassic (323 – 174 MYA) . During this time the sedimentation recorded a gradual change from a glacial environment to an arid desert, as South Africa changed in latitude from the polar region to the tropics . The Karoo basin is the only basin globally to record this 200 MY change in its sedimentation . It spans 700,000 km2, covering 60% of South Africa’s land surface . Only the South Western portion of this is the modern-day Karoo region. Due to the geological history of the basin, it is now of large economic value due to expansive coal deposits .
The modern-day Karoo region of South Africa is an arid/semi-arid area that spans one third of the land surface of South Africa . The Karoo comprises two separate biomes, namely Nama Karoo and Succulent Karoo, which are distinguished by climate and vegetation . The Nama Karoo is on the central plateau in the western portion of the country . It experiences unreliable summer rainfall with periods of prolonged drought . The vegetation is dominated by dwarf shrub vegetation which are xeromorphic as well as succulents in the west and grasses in the east . This is the second largest biome in South Africa covering 260,295 km2 . Due to past landuse practices approximately 60% of the biome has moderate to severe degredation of soils and vegetation . Only 2% of the entire Nama Karoo biome is under conservation . The Succulent Karoo covers a belt from Lüderitz (Namibia) through Namaqualand and includes smaller areas of Hantam, Tanqua, Roggeveld and the little Karoo . The biome experiences reliable winter rainfall (100-200 mm anually) which aids in the sustainability of vegetation . The vegetation is dominated by succulent plants and following good rains by annuals (Asteraceae and Brassicaceae) . This biome is the forth largest in South Africa and covers 87,001 km2 . The succulent Karoo is bordered by the Cape Fold mountains, which caused isolation leading to high levels of endemisim and species richness of many taxa including hopliniid beetles, aculeate Hymenoptera, reptiles and arachnids . The succulent Karoo is also the world’s only entirely arid region diversity hotspot . Despite high levels of endemisim and being a biodiversity hotspot, only 8% of the biome is conserved .
Stasimopidae is a family of trapdoor spiders endemic to Southern Africa . The family consists of one genus, Stasimopus and 56 described species . These spiders have life history traits which make it easy to detect population structuring and dispersal events increasing the likelihood of inferring phylogeographic events. Mygalomorphs are exceptionally long lived for spiders, reportedly living to 43 years old . Most mygalomorph spiders live in retreats comprising vertical burrows or chambers under rocks or on trees which are lined with silk . The females show great fidelity to their burrows, hunting from burrow entrances . The males are nomadic, wandering to locate females to mate with and are thus responsible for nuclear gene flow between populations. The offspring, once mature enough, will leave the mothers burrow but only move a few meters before making a new burrow to live in . This combination of behaviours leads to extensive population structuring and isolated geographic locations for the populations (Rix et al., 2017). These characteristics are often associated with species which are classified as ‘short range endemics’, which if found to be true for the species of the genus, may make them of conservation concern.Stasimopus and other mygalomorph spiders are model species for phylogeographic studies due to these factors . Performing this study on the Stasimopus genus, could possibly serve as a proxy for other mygalomorph spiders living under similar environmental conditions.
Several phylogeographic studies have been performed on Mygalomorphae species, but none have to date been performed in South Africa, nor on the Stasimopus genus . Phylogeographic inference is of immense importance to conservation as there is the possibility of defining areas for conservation based on the evolutionary potential of various taxa . This is vital in light of the sensitivity of the Karoo ecosystem, the life history of Stasimopus and the drastic land-use and climate change predicted for the area.
The aims of this study are threefold; first, to create a dated phylogeny for the Stasimopus species occurring in the Karoo region using CO1, 16S and EF-1ɣ genes. This will be used to understand the diversification of the genus over geological time. Second, using haplotype networks to understand the distribution of genetic diversity in the landscape. Lastly, evaluating the phylogeographic pattern underlying the phylogeny and assessing the potential drivers thereof.