SAAB Webinar Invitation – Dr Daniel Zhigila

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Meeting ID: 997 0197 8600
Passcode: 053956


Title: Systematics and extinction risk patterns in Thesium (Santalaceae)

Recent phylogenetic studies circumscribed the genus Thesium as monophyletic by including four segregate genera: Austroamericium, Chrysothesium, Kunkeliella and Thesidium. Additionally, the Greater Cape Floristic Region (GCFR) Thesium, having both ecological specialists and generalists, typifies an appropriate system for evaluating both the correlates of range extent and specialization, and the relative extinction risks associated with both. For my PhD, we tested the monophyly of the genus Thesium and its infrageneric taxa using expanded taxon sampling and phylogenetic analyses. One of the key objectives is to develop a well-resolved phylogeny that will allow a piece-wise revision of complex clades. Further, we tested the hypothesis that range size, ecological specialization and extinction risks are phylogenetically structured and then asked whether these will impact Thesium phylogenetic diversity. For the later, we quantified and modelled the niche breadth for each species based on the contemporary geographic range extents and ecological specializations. Key novelties include: i) establishment of an infrageneric classification scheme based on an integrative approach for the genus. This classification recognized five monophyletic subgenera, reflecting evolutionary relatedness and each supported by unambiguous morphological characters; ii) a detailed taxonomic revision for the T. subgenus Hagnothesium, comprising eight species which are all endemic to the Cape Region; iii)  discovery and description of eight species new to science, the majority of which are restricted to the highly fragmented agricultural landscape in the Agulhas Plain; iv) our data suggest a strong positive correlation between environmental variables and species range extents. However, the range extent, ecological specializations and extinction risk are phylogenetically random; and iv) the conservation status of the Cape Thesium was provided to aid in developing conservation strategies in the face of accelerated climate change.

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