Hotspots of intraspecific diversity: how are morphologically distinct populations generated and maintained within a species?

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Many species, including humans, show morphological variation. Not all members of the species look the same, and they may vary in any number of traits. The presence of this morphological variation is very important, because it is a source of evolutionary change. Since populations contain individuals with different characteristics, natural selection may work to favour certain forms and repress others, or it may be the case that different forms are successful in different parts of the range of the organism, generating multiple species from a single starting species. In this project we aim to understand how morphological variation within a species is produced genetically, how variation is affected by natural selection resulting from ecological context, and how such variation is maintained when varieties meet. By understanding the production and maintenance of morphological variation we will gain greater insight into how evolution and speciation occur and provide input into models of how different species will respond to the various challenges that might occur as a result of climate change.We have developed a South African daisy species, Gorteria diffusa, as the best model system for this work. Gorteria produces classic "daisy" flowerheads composed of small circular disk florets in the centre and large elongated ray florets round the outside. All the florets are orange but some of the ray florets sometimes produce raised black spots that mimic the fly that pollinates the species. Within Gorteria's range in South Africa it exists as around 15 distinct forms (called morphotypes), each of which has a unique combination of floral traits, such as ray floret number and colour, presence or absence of spots, number of spots, presence and position of highlights in the spot, and presence and position of papillae in the spots. This species therefore provides an excellent example of extreme morphological variation, but is nonetheless easy to collect, grow and work with. The relative immobility of plants removes problems of migration and self-selection of environment. We have established procedures for molecular biological work with Gorteria. We can perturb gene expression using transgenic approaches, a very powerful way of understanding how genes control plant morphology. We have a good understanding of the molecular genetic basis of the development of a single petal spot type. We have also developed a strong collaboration with Dr Allan Ellis, a pollination ecologist at the University of Stellenbosch, South Africa, who will help with this project by providing support in the field.We have already defined how the different morphotypes of Gorteria are related to one another. In this project we will map different aspects of floral morphology and pollinator behaviour onto this phylogenetic tree to understand which direction evolution has taken for each trait and how many times each trait has evolved. Working together in the field, we will quantify the ecological context of each morphotype to understand how selection has favoured different morphologies in different geographic locations, and then test the hypotheses we generate by transplanting plants between different sites. We will then define the molecular evolution underpinning this morphological evolution - analysing what changes to key genes have allowed the visible changes we observe. Finally, to explain why morphologies don't merge into a continuum when populations meet, we will analyse the morphology and genetic structure of Gorteria populations at the places where different morphotypes meet, and explore post-zygotic isolation between morphotypes.Taken together, these data will give us an integrated eco-evo-devo understanding of how this enormous variation in flower types exists within Gorteria, providing us with insight into how species radiate so rapidly in the Cape Flora and other biodiversity hotspots.