What drives evolutionary diversification in a biodiversity hotspot? A `next generation´ phylogenetic approach comparing three clades of the Cape Floristic Region´s mega-genus Erica

• Applicant: Dr. Nicolai M. Nürk, since 12/2018
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: from 2014 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 251415172

The Cape Floristic Region (CFR) of South Africa is a botanical hotspot and represents an ideal system with which to investigate biological diversity. The total area of the CFR is small but the number of plant species found there is disproportionally high, and an astonishing 70% of them are found nowhere else in the world. The largest Cape clade, the genus Erica (Ericaceae), alone accounts for 7% of the flora, making it a key taxon for understanding the causes of evolutionary diversification. In a renewal of my current DFG-funded project, I propose to test a number of the most likely factors proposed as potential causes of the high plant diversity of the CFR, principally those relating to shifts in geographic range and pollinators. Extending from the original aims, we would compare three groups of closely related Erica species: the imbricata/coccinea-clade (data collected in current project), the abietina/viscaria-clade, and E. plukenetii. The clades comprise a total of c. 34 species, with often highly localised geographic distributions. They are each characterised by variation in floral macro-morphological characters that are generally related to pollination by different vectors. The recent divergence of the species and populations in these clades means that phylogenetic evidence for evolutionary events, such as dispersals, may remain unmasked by subsequent events. However, reticulate processes, such as hybridisation, and coalescent stochasticity can result in considerable differences between gene trees when comparing closely related individuals and clades, as is apparent in our imbricata/coccinea-clade dataset. Accurate phylogenetic inference is only possible under these circumstances if we sample numerous, meaningfully resolved independent gene trees and model the processes underlying their differences appropriately. To this end, I propose to use our Erica-optimised hybridisation capture and high-throughput sequencing pipeline to obtain 132, up to c. 7 Kb long DNA sequence markers for each of 72 representative specimens of the two additional clades. For improved sampling of populations, we will use a multiplex PCR approach to obtain a subset of the markers for up to 192 further samples. By analysing the data with coalescence-based methods we can infer meaningful, potentially reticulate, species trees. The species trees of all three clades can then be used with further phylogeny-based inference methods as independent tests of competing hypotheses of geographic range and character evolution. Plausible hypotheses to be tested with this data include allopatric speciation models and the Grant-Stebbins model for pollinator driven speciation. In so doing we can yield profound insight into the processes driving the divergence of species, both in the Cape, and in general.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Michael Pirie, until 12/2018