The phylogeography and diversification of an endemic trapdoor spider
genus, Stasimopus Simon 1892 (Araneae, Mygalomorphae, Stasimopidae) in
the Karoo, South Africa
Abstract
Aim: The genus Stasimopus is endemic to South Africa but has never
undergone a phylogeographic review. This study aims to unravel the
phylogeographic patterns and history of the many Stasimopus species
which occur in the greater Karoo region. Location: The Karoo region,
South Africa Time period: 2017-2018 Major taxa studied: Cork-lid
trapdoor spider, Stasimopus (15 species). Methods: A fossil-calibrated
phylogeny was produced based on three gene regions (CO1, 16S and EF-1ɣ)
for Stasimopus specimens collected in the Karoo region, to infer dates
of origin and diversification. Demographic analyses were performed on
species with sufficient sample sizes (>4). Haplotype
networks were constructed for each gene region and plotted on a map to
infer phylogeographic patterns. Lastly, Mantel tests were performed to
test for isolation by distance. Results: It was found that 15 species
occur in the Karoo and that the genus radiation in the area is in the
early Paleocene. Most diversification occurred between the late Eocene
and the Miocene. Several species show signals of demographic expansions.
Isolation by distance was detected, but only with a slight correlation.
Main conclusions: It is apparent that aridification has played a vital
role in the diversification of the genus in the Karoo region. This is a
shared biogeographic influence between the mygalomorph fauna of the
Karoo and arid region of western Australia. Stasimopus has radiated from
the late Eocene and through the Miocene resulting in 15 extant species
in the region. The Tankwa Karoo has been identified as a possible
Pleistocene glacial cycle refugia for the species S. leipoldti. Many of
the species in the Karoo are short range endemics, making them of high
conservation concern. This study provided vital information as the Karoo
is undergoing further desertification due to factors such as climate
change, which may affect the future of short-range endemic spiders.