Taxonomy and systematics of the Bangiales (Rhodophyta) in South Africa using an integrative approach

Doctoral Thesis


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University of Cape Town

The Bangiales is a globally distributed red algal order that is best known for its economic value in the nori industry. The morphological simplicity of the Bangiales offers limited distinguishing characters for taxonomy and the order was therefore broadly classified into two genera based on morphology: the bladed Porphyra and filamentous Bangia. However, in 2011, a taxonomic revision of the Bangiales based on a two-gene phylogeny identified 15 genera. Since then, an additional bladed genus and numerous species have been added to the order. The Bangiales were first recorded in South Africa in 1843 when Porphyra capensis Kützing was described. Since then several changes have been made to the bangialean flora of South Africa with many new species discovered based on morphological identification. In 2004, a preliminary molecular assessment of Poprhyra along the South African coast revealed far greater species diversity than previously recorded. Following the taxonomic revision by Sutherland et al. (2011), some species from South Africa have been transferred to the genus Pyropia, others remain in Porphyra and many others have not yet been re-assessed. At present, three genera; the filamentous, Bangia and the bladed Porphyra and Pyropia have been recorded in South Africa, and comprise numerous species (based on morphology) and molecular entities. In the present study a comprehensive collection of newly collected and herbarium specimens (collectively ca. 300 specimens from ca. 50 sites) of the Bangiales from South Africa was analysed. A total of 241 sequences were generated for three unlinked loci (nSSU, rbcL & cox1). Taxa were identified or delimited via an integrative taxonomic approach using molecular, morpho-anatomical and ecological data. Species were delimited using three DNA-based species delimitation methods (ABGD, GMYC, PTP) applied to the mitochondrial gene cox1 (n=203) and the plastid gene rbcL (n=80). A multigene phylogeny was also constructed (nSSU, rbcL & cox1) and used to delimit species. Subsequent morpho-anatomical analyses complemented with ecological data and herbarium specimens (South Africa and Namibia) showed that 16 species in three genera (11 Porphyra, four Pyropia and one Bangia) are present along the South African coast. Morpho-anatomical characters of two species with uncertain taxonomic status were consistent with the descriptions of two widespread species, Bangia cf. fuscopurpurea and Py. cf. suborbiculata but remain to be confirmed using a molecular approach. In addition, two new species, Pyropia meridionalis sp. nov. and Porphyra agulhensis sp. nov. were described. Pyropia meridionalis is a kelp-associated species that is commonly found on the kelp limpet, Cymbula compressa, or on the stipes of Ecklonia maxima, and rarely on other species of southern African kelp, Laminaria pallida and E. radiata or other algae. This species occurs along the southwest and west coast of South Africa throughout the year, but may extend to Namibia. Pyropia meridionalis was shown to be previously misidentified as Py. gardneri in South Africa. This species was not closely related to other southern African endemic species of Pyropia, suggesting that species colonized and spread along this coastline independently. Nevertheless, most species shared close genetic affinities to other Southern Hemisphere taxa. This supports the notion of historic connectivity in the Southern Ocean proposed for red algae. Porphyra agulhensis is characterized by delicate laciniate rosette blades and a distinct greenish to pale pinkish-purple colour. This species was shown to be historically misidentified as P. capensis and is restricted to the Agulhas Marine Province on the south coast of South Africa. It includes one cryptic species (RSAj). The remaining eight molecular species of Porphyra formed a monophyletic group and occurred along the Benguela Marine Province on the west coast of South Africa. No single morpho-anatomical or ecological character could distinguish between these molecular species. Despite overlapping conventional morpho-anatomical or ecological characters among cryptic species, all features were within the range of the current description of P. capensis and were therefore referred to as the P. capensis cryptic species complex (PCC). High genetic diversity and several major lineages were identified in the PCC along the Benguela Marine Province. Conversely, the Porphyra agulhensis cryptic species duo along the Agulhas Marine Province presented low levels of genetic variation with ca. 70% of individuals belonging to a single haplotype group. Genetic diversity within Porphyra in South Africa was higher on the west coast of South Africa than on the south coast and the region between Cape Agulhas and Cape Point was identified as a region of major biogeographic change. Historic and contemporary processes, which likely shape present-day genetic patterns in South African Porphyra, are discussed. Similar to Pyropia, species of Porphyra from South Africa shared a close phylogenetic affinity with some Chilean bladed Bangiales, providing further support for historic connectivity in these red algae in the Southern Ocean. South Africa is now home to the second highest number of species of Porphyra in the world and shares three species of Pyropia with Namibia (based on morphological identification). All species identified using molecular sequences appear to be endemic to South Africa or southern Africa. The extensive genetic diversity found along the South African coast compares well with other Southern Hemisphere countries, such as Chile and New Zealand. The Southern Hemisphere has been suggested as the origin and centre of diversity for the Bangiales, but still remains relatively unexplored, and further investigations are likely to yield further species and species links.