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

Lead Research Organisation: University of Cambridge
Department Name: Plant Sciences

Abstract

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.

Planned Impact

IMPACT STATEMENT Understanding how morphological variation is produced and maintained has long term implications for our understanding of evolution, in particular speciation, and for the design of strategies to conserve biodiversity. Understanding how these particular insect-attracting structures are produced in their various forms has the potential to impact on sustainable production of animal-pollinated crops, utilizing conventional or transgenic-based breeding systems. Our project therefore has potential impact in several sectors, as well as providing great opportunities for public engagement.

CONSERVATION IMPACT Variation is essential to the evolutionary flexibility of populations and species faced with challenges such as changing climate, changing range or changing community profiles. Our data will provide input into models for the maintenance of variation and thus biodiversity. We anticipate that this work will have particular impacts for stakeholders with an interest in plant biodiversity (such as members of the UK Biodiversity Partnership) and plant conservation (such as Plantlife International and members of the Global Partnership for Plant Conservation). We will disseminate data to conservation and biodiversity stakeholders through the Cambridge Conservation Initiative (CCI). The CCI links a number of conservation charities and NGOs with the University of Cambridge. We will link our project to the CCI webpage, provide updates on the News section, and advertise seminars through their diary section. In South Africa the work is directly relevant to organisations involved in biodiversity conservation, especially in the Succulent Karoo Biodiversity Hotspot, such as the South African National Parks Board, Botanical Society SA, Succulent Karoo Ecosystem Programme, Western and Northern Cape Nature Conservation. The insights we provide will be displayed in local visitor centres and enrich the experience of botanical ecotourists, on whom much of the local economy depends.

AGRICULTURAL IMPACT Farmers of animal-pollinated crops face particular challenges as pressure for enhanced productivity is coupled with changes to pollinator populations. An understanding of how diverse insect-attracting structures are produced using a defined set of genes and developmental pathways will feed into our understanding of how genetic pathways control development of animal-attracting flowers. We will disseminate data to farmers and breeders, and increase our engagement with stakeholders, through activities at the University and at NIAB. We will target outreach to these stakeholders through BJG's current contacts with Syngenta and a number of plant breeders. Results will be demonstrated at NIAB Innovation Farm Open Days and Symposia. Additional opportunities to interact with industry will be through the University's "Enterprise Tuesdays", where research can be presented to a range of interested companies.

IMPACT THROUGH PUBLIC ENGAGEMENT is nationally and internationally increasingly important. Current activities include presentations at public engagement events including National Science Week, the Cambridge Festival of Plants and the Cambridge Festival of Ideas. Enhanced public impact activities will include linking our project to the CCI webpage, providing News updates and advertising seminars through their diary section, and setting up a project-specific webpage giving project details and accessible introductions to the concepts involved. In addition, we will work with the Horticulture, Education and Interpretation staff at Cambridge University Botanic Garden to develop a trail with appropriate interpretation material (and boards and linked through QR codes to the project website) to explain speciation through pollinator specificity to a general audience. CUBG has 250,000 casual visitors per year, plus 10,000 schoolchildren on arranged visits, so this display will reach a large and varied audience.

Publications

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Fattorini R (2018) Joining the dots. in Nature plants

 
Description We have identified a set of genes involved in petal spot differentiation, including some surprising genetic modules.
Exploitation Route We will functionally characterise these genes to validate their role.
Sectors Agriculture, Food and Drink

 
Description Pollination in Gorteria diffusa 
Organisation University of Stellenbosch
Country South Africa 
Sector Academic/University 
PI Contribution We provide the manpower and understanding to analyse genetic variation across populations of Gorteria occupying different pollinator niches.
Collaborator Contribution ALlan Ellis provides local knowledge, knowledge of geographic locations of populations, and field assistance.
Impact SOme papers, although more to come.
 
Description Article in Botanic Garden newsletter 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact An article on the project in the Cambridge Botanic Garden Friends' Newsletter.
Year(s) Of Engagement Activity 2018