Evolution in action: what drives the generation of new mutations in the Harebell, (Campanula rotundifolia)?

Overview

We often think of evolution as occurring over long timescales but in fact, it can occur rapidly, with dramatic changes possible even within a generation. As climate change accelerates, understanding the extent to which evolutionary change might play a role in how species respond has taken on increasing importance.

The Scottish bluebell or harebell (Campanula rotundifolia) is a small but charismatic species with a wide circumpolar distribution. We have done extensive work to show that, in the UK and Ireland, the species maintains two spatially separated, differently polyploid populations – a pattern most likely laid down during colonisation following the last Ice Age (Fig 1). However, at a few distinctive locations, we found new genetic variants, which must have arisen more recently from local populations. What drives this local evolution and allows the new variants to persist remains unclear.

Building on an extensive database of knowledge about the species, this project aims to identify the primary forces generating new genetic variation in C. rotundifolia, how new variants persist in the face of competition from the predominant local type, and the role such adaptability might have in the species’ future. Given the wide distribution C. rotundifolia occupies, the findings are likely to have implications for habitats around the world.

Although the candidate will determine the final direction of the project, we expect that the following would be core questions:

• What drives in situ polyploidisation (6x evolving from 4x populations in specific locations)?
• Do spatially differentiated breeding barriers exist and what are the conditions for their persistence?
• Is allopatry maintained among chromosome races by evolutionary or ecological pressures?

Click on an image to expand

Image Captions

Fig. 1: Cytotype distribution in Harebell populations
Fig. 2: Harebell (Campanula rotundifolia).

Methodology

The project will conduct detailed analysis of populations in the field at 3 sites to determine the fine-scale local distribution of different cytotypes, alongside detailed evaluations of the local environment. Individual plants will be mapped and sampled for subsequent genotyping and cytotype determination via flow cytometry. Local patterns of spatial genetic organisation will be compared to environmental variables to identify primary drivers of spatial partitioning. Parallel experimental work will use individuals sampled from populations in which cytotypes occur in sympatry / isolation to undertake controlled crosses and subsequent progeny testing. Crosses will be undertaken in a range of controlled environmental conditions representative of the primary environmental drivers at the home sites, to evaluate the extent to which mutational change is mediated by specific environmental factors. Competition experiments will be carried out to evaluate the fitness of progeny from different environments / genetic backgrounds. The candidate will have the opportunity to learn a range of methods to explore traits of the species likely to be of life history significance, such as growth, physiology and reproduction, and evaluate extent and patterns of variation through measurement in experimental trials. Full training in statistical techniques will be provided including, use of mixed models to evaluate components of variation, sequence data handling, population genetic analysis.

The candidate will also have the opportunity to take the project beyond the UK & Ireland distribution to study populations across its worldwide range.

Project Timeline

Year 1

Literature review, including survey of drivers for elevated mutation rates and polyploid advantage.
Field season 1 – sample and data collection.
Glasshouse experimental work.

Year 2

Lab and Data analysis.
Field season 2: sample and data collection.
Glasshouse experimental work.

Year 3

Molecular lab work, data collection and analysis.

Year 3.5

Finalise data analysis and write up.

Training
& Skills

The project will provide the candidate with training in experimental design, quantitative trait analysis, evaluation of spatial variation, molecular lab techniques and data analysis. The project represents an opportunity for broad training in methods and approaches that will equip a successful student for a range of future careers. In addition, the student will receive training, advice and guidance on data handling and statistics, presentation, scientific writing and production of published work from a diverse and experienced team of supervisors.

References & further reading

Soltis & Soltis (2000) The role of genetic and genomic attributes in the success of polyploids. Proceedings of the National Academy of Sciences, 97, 7051-7057.

Stevens, Wilson & McAllister (2012) Biological Flora of the British Isles: Campanula rotundifolia. Journal of Ecology. 100(3): 821-839

Sutherland & Galloway (2018) Effects of glaciation and whole genome duplication on the distribution of the Campanula rotundifolia polyploid complex. American Journal of Botany, 105(10), 1760-1770.

Further Information

Stephen Cavers: scav@ceh.ac.uk, 0131 445 8552

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