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.