Browsing by Author "Oberlander, Kenneth C."
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- ItemConsistent phenological shifts in the making of a biodiversity hotspot : the Cape flora(BioMed Central, 2011-02) Warren, Ben H.; Bakker, Freek T.; Bellstedt, Dirk U.; Bytebier, Benny; Claszen-Bockhoff, Regine; Dreyer, Leanne L.; Edwards, Dawn; Forest, Felix; Galley, Chloe; Hardy, Christopher R.; Linder, H. Peter; Muasya, A. Muthama; Mummenhoff, Klaus; Oberlander, Kenneth C.; Quint, Marcus; Richardson, James E.; Savolainen, Vincent; Schrire, Brian D.; Van der Niet, Timotheus; Verboom, G. Anthony; Yesson, Christopher; Hawkins, Julie A.ABSTRACT: Background: The best documented survival responses of organisms to past climate change on short (glacial-interglacial) timescales are distributional shifts. Despite ample evidence on such timescales for local adaptations of populations at specific sites, the long-term impacts of such changes on evolutionary significant units in response to past climatic change have been little documented. Here we use phylogenies to reconstruct changes in distribution and flowering ecology of the Cape flora - South Africa's biodiversity hotspot - through a period of past (Neogene and Quaternary) changes in the seasonality of rainfall over a timescale of several million years. Results: Forty-three distributional and phenological shifts consistent with past climatic change occur across the flora, and a comparable number of clades underwent adaptive changes in their flowering phenology (9 clades; half of the clades investigated) as underwent distributional shifts (12 clades; two thirds of the clades investigated). Of extant Cape angiosperm species, 14-41% have been contributed by lineages that show distributional shifts consistent with past climate change, yet a similar proportion (14-55%) arose from lineages that shifted flowering phenology. Conclusions: Adaptive changes in ecology at the scale we uncover in the Cape and consistent with past climatic change have not been documented for other floras. Shifts in climate tolerance appear to have been more important in this flora than is currently appreciated, and lineages that underwent such shifts went on to contribute a high proportion of the flora's extant species diversity. That shifts in phenology, on an evolutionary timescale and on such a scale, have not yet been detected for other floras is likely a result of the method used; shifts in flowering phenology cannot be detected in the fossil record.
- ItemNitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis(BMC (part of Springer Nature), 2019-10-23) Jooste, Michelle; Roets, Francois; Midgley, Guy F.; Oberlander, Kenneth C.; Dreyer, Leanne L.Background: Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is confined mostly to crop plants, and to date no such system has been reported for geophytes. Methods: Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds. Results: Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds. Conclusions: The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously expected.
- ItemNomenclatural notes on southern African Oxalis species(AOSIS, 2018) Dreyer, Leanne L.; Oberlander, Kenneth C.; Klopper, Ronell R.Background: The correct author citation of Oxalis sonderiana (Kuntze) J.F.Macbr. and the validity and identity of the species Oxalis beneprotecta R.Knuth, Oxalis bullulata T.M.Salter and Oxalis pulchella Jacq. var. beneprotecta (R.Knuth) T.M.Salter are unclear. Objectives: To resolve the nomenclatural and taxonomic confusion surrounding these four taxa. Method: We studied relevant herbarium records (especially type material) of all the taxa, and paired this with scrutiny of all publications that bear reference to the nomenclature and taxonomy of these species. Results: The correct author citation for Oxalis sonderiana has been determined; Oxalis bullulata is confirmed as a distinct species, and the continued recognition of Oxalis beneprotecta as a variety of Oxalis pulchella is suggested. It is further ascertained that the name ‘Oxalis nidulans Turcz.’ is not a later homonym, but a reference to a misapplication of Oxalis nidulans Eckl. & Zeyh. to the type specimen of Oxalis sonderiana. Conclusion: These results clarify the current confusion surrounding these taxa in global herbaria and in national and international databases.
- ItemOxalis seeds from the Cape Flora have a spectrum of germination strategies(Botanical Society of America, 2019) Jooste, Michelle; Midgley, Guy F.; Oberlander, Kenneth C.; Dreyer, Leanne L.PREMISE OF THE STUDY: Seed germination strategy has profound ecological and evolutionary consequences, with transitions between germination strategies receiving renewed recent attention. Oxalis from the Cape Flora, South Africa, has seeds with two contrasting germination strategies: orthodox and recalcitrant. The morphological gulf between these strategies (and potential intermediate morphologies) has been poorly quantified, with questions regarding their ecological function and evolution. We reconsidered this binary classification, emphasizing potential intermediate states. METHODS: Seed physiological traits were used to assign strategies to 64 Oxalis species. We tested for morphological/phenological signal corresponding to defined strategies with cluster, principal component, Kmeans clustering and discriminant analyses. KEY RESULTS: We show that an intermediate germination strategy does exist among Cape Oxalis, with two possible morphological groups within each strategy. These could reflect a continuum of germination states, where an ancestral orthodox strategy evolved towards a maximally recalcitrant peak, with a mosaic of intermediate states reflected in extant taxa. CONCLUSIONS: Environmental factors may affect germination strategy and distribution throughout the Cape because recalcitrant and intermediate species are confined to the winter rainfall region. They occupy specialized niches and may face adverse impacts under predicted climate change (hotter and drier winters), meriting focused future conservation.
- ItemThe phylogenetic significance of leaf anatomical traits of southern African oxalis(BioMed Central, 2016-10) Jooste, Michelle; Dreyer, Leanne L.; Oberlander, Kenneth C.Background: The southern African Oxalis radiation is extremely morphologically variable. Despite recent progress in the phylogenetics of the genus, there are few morphological synapomorphies supporting DNA-based clades. Leaflet anatomy can provide an understudied and potentially valuable source of information on the evolutionary history and systematics of this lineage. Fifty-nine leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades. Results: A combination of 6 leaflet anatomical traits (stomatal position, adaxial epidermal cells, abaxial epidermal cells, mesophyll, sheath around vascular tissue, degree of leaflet conduplication) clearly support various clades defined by previous DNA-based phylogenetic work. Other, mostly continuous leaflet anatomical traits were highly variable and showed less phylogenetic pattern. Conclusions: Major and unexpected findings include the transition from ancestral hypostomatic leaflets to adaxially-located stomata in the vast majority of southern African Oxalis, the loss of semi-swollen AB epidermal cells and the gain of swollen adaxial and abaxial epidermal cells in selected clades, and multiple changes from ancestral bifacial mesophyll to isobilateral or homogenous mesophyll types. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region and provide a basis for future hypotheses regarding its radiation.