Under the trapdoor - resolving the taxonomy and phylogeography of the trapdoor spider genus Stasimopus (Mygalomorphae: Stasimopidae) of the Karoo

Abstract

Stasimopus is a genus of cork-lid trapdoor spider under the infraorder Mygalomorphae. The genus is endemic to southern Africa, but is largely understudied. This study was undertaken to understand the true species diversity and history of this genus in the Karoo region of South Africa. The Karoo is a semi-arid, unique and sensitive ecosystem which is facing pressure for development due to economic incentives. This area has long been neglected, with few studies investigating the fauna and their phylogeographic history.

The first two data chapters are dedicated to finding new methods to aid in species identification. The identification of Stasimopus as well as mygalomorph species generally has been a long-standing challenge. This is due to their conservative morphologies and the lack of quantifiable characters. For this reason, species delimitation methods as well as geometric morphometrics were explored to find ways to aid species identification. Multiple coalescent based species delimitation methods were used in chapter 2 to attempt to determine the number of different species present for Stasimopus in the region. These methods were tested against the morphological identifications and monophyletic groupings. The species delimitation proved unfruitful, as they appear to delimit population structure rather than species. This is likely due to extensive population structuring, which is common in mygalomorph spiders. The second methodology was to test whether the historically used eye patterns are a valid character for species identification and if so, to implement geometric morphometric techniques to attempt to separate species. The results showed significant phylogenetic signal for ocular patterns in both sexes, validating its use for species identification. Species and morphospecies show distinct clustering in morphospace, but there is overlap due to the continuous shape of the character. The methodology of applying geometric morphometrics to quantify ocular patterns shows great promise for distinguishing species, but a larger sample size is required to test this more conclusively.

The third data chapter is the first integrative taxonomy for Stasimopus of the Karoo region of South Africa. The study found that the diversity of the genus is significantly higher than previously believed including the description of nine new species. This chapter also highlights the pitfall of using only morphological data as the male of S. maraisi was incorrectly assigned to the female based on morphology. A description of the genetically matched S. maraisi male was completed as well as the original male being assigned to a new species.

The final data chapter unravelled the phylogeographic patterns of the genus in the Karoo. It was found that 15 species occur in the region and that the genus radiated in the Karoo in the early Paleocene. Most species radiated between the late Eocene and the Miocene, which is mirrored by some mygalomorph spiders in the arid region of Western Australia. The Tankwa Karoo has been tentatively identified as a Pleistocene glacial cycle refugia for the species S. leipoldti. The species S. maraisi was found to have undergone extensive population expansion in the mid-Miocene leading to its extensive modern range. This chapter also highlights the large number of short-range endemics present in the Karoo, which are of great conservation concern.