Rapid Evolution During Invasive Range Expansion

Range expansions by invasive species increasingly threaten biodiversity and present large costs to society. However, prediction of invasion remains challenging, partly because invasive range expansion can be an engine for evolutionary change that alters invasive behaviour. Indeed, the rapid evolution of invasiveness remains poorly understood, hampering efforts to understand and manage invasion risk.

The goal of this studentship is to discover how evolutionary forces on ecological time scales play a crucial role in successful biological invasions. The student will use Danish scurvygrass (Cochlearia danica) as a model system to test hypotheses about evolution during invasive range expansion. Native to the UK coastal fringe, this salt-tolerant winter annual plant has invaded inland road verges in the last 50 years due to winter salt-treatment and vehicle dispersal. This offers a powerful system to study replicated invasion fronts on different roads, in close proximity to native populations.

We expect that that Danish scurvygrass invasion will have been associated with strong selective pressures from range expansion itself (spatial selection caused by repeated founder effects at the invasion front) and the colonisation of a novel environment. This leads to the following main hypotheses that will be tested by the student:

1. Selection during range expansion should favour traits that enhance dispersal, population growth rates and tolerance for the stresses of inland roadsides, such as pollution and more extreme temperatures.
2. Counter to hypothesis 1, different selective forces could have opposing effects on species’ traits, impeding the evolution of invasiveness. This could reflect simple life history trade-offs but could also be caused by more subtle genetic correlations between different traits that arise because of quantitative trait pleiotropy or linkage disequilibrium across the genome.
3. Evolution of increased invasiveness may occur through the erosion of genetic correlations that constrain the action of different selective forces on multiple traits.

To test these hypotheses the student will employ experimental, theoretical and population genetic approaches to answer 3 major questions:

1. Has C. danica undergone rapid evolutionary change during its invasive range expansion? A common garden experiment will be performed with seed collected from paired invasive and native populations across the UK.

2. What selective forces have driven this evolutionary change? Data from the common gardens will be used to parameterise simple demographic and dispersal models to predict whether observed trait adaptation leads to greater population growth and/or dispersiveness. The student will test whether genetic correlations have been eroded in invasive populations, consistent with evolution of increased invasiveness. To test whether invasive populations have evolved increased stress tolerance of polluted soil and extreme low temperatures, performance experiments will be carried out.

3. What are the population genetic consequences of invasion? Neutral genetic markers will be used to test whether genetic diversity is reduced at the invasion front, and to infer whether inland populations result from multiple invasion events or a single event. The student will complete an external placement in the laboratory of Dr Levi Yant at the John Innes Centre to explore how their results fit within emerging understanding of the wider genomic dynamics of Cochlearia species and their adaptation to extreme environments.

Further details of the project can be found at http://www.iapetus.ac.uk/wp-content/uploads/2017/11/IAP-17-68-Chapman-CEH.pdf. The student will be primarily based at CEH Edinburgh, with the degree awarded by University of Stirling (supervisor Mario Vallejo-Marin) and a placement at the John Innes Centre.

The successful candidate will have a strong background in quantitative ecology, biology or evolution. A demonstrated interest in the biology of invasive species and eco-evolutionary dynamics is desirable. Experience of GIS, coding in R and scientific publication are also desirable, although training in all these will be provided.

Applicants for a studentship must have obtained, or be about to obtain, a 2.1 degree or higher. If you have a 2.2 degree, but have also obtained a masters qualification, you are also eligible. Substantial relevant post-graduate experience may also be sufficient, please contact the supervisors for more information.

Please see http://www.iapetus.ac.uk/aboutstudentships/ for details of how to apply.