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Genetic Structuring of a Plant, Herbivore and Parasitoid Metacommunity

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  • Full or part time
    Prof J Bullock
    Dr D Hodgson
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Across landscapes, ecological communities vary in structure and dynamics. Metacommunity theory suggests that this variation is governed by dispersal, coupled with selection pressures imposed by local biotic interactions and abiotic conditions. Understanding these processes is fundamental for predicting large-scale biodiversity responses to environmental change. This project will progress towards this understanding by quantifying genetic structuring of interacting species at three trophic levels across a landscape. The student will test the hypothesis that genetic structuring of herbivores and their parasitoids is governed by the structure of the food plant metapopulation. The project combines fundamental research into metacommunity theory, with applied relevance: the species studied are wild relatives of important crop plants, pests and natural enemies.

The metacommunity is a set of local communities that exchange dispersers of interacting species. The varying structure of communities in a landscape is driven by species’ abilities to disperse among habitat patches and the interactions among these species within local communities. Testing metacommunity theory in the real world requires data on environmental variation, genetically-determined traits, species interactions and dispersal and gene flow in multiple interacting species.

Wild cabbage Brassica oleracea grows along Dorset’s cliffs. Its tissues contain glucosinolates (GS), secondary metabolites that provide anti-herbivore defence. The types and concentration of GS are genetically-determined and vary greatly among the Dorset populations. The cabbage aphid Brevicoryne brassicae is affected by GS in this system, and is fed on by the parasitoid Diaretiella brassicae. We hypothesise that:

H1. Due to poor dispersal, wild cabbage populations are highly differentiated genetically.
H2. Although cabbage aphids are under selection pressure due to genetic differentiation among cabbage populations, there is little local genetic structuring due to high dispersal ability and colonisation from crop pests.
H3. Genetic structuring of the parasitoid will correlate with that of the cabbages, due to cascading effects of secondary chemistry up the trophic levels, coupled with poor dispersal ability.

These hypotheses will be addressed by: a) field sampling of all three species across the metacommunity; b) laboratory analysis of this material using microsatellite and/or restriction site associated DNA markers; and c) statistical analysis using Bayesian clustering methods to assign individuals to genetically distinct populations. Common garden experiments will determine whether natural population genetic structures are forced by natural selection or by landscape fragmentation.

The student will be based as CEH Wallingford, and will be registered and also work with Biosciences at Exeter University (Prof Dave Hodgson at Penryn Campus, Cornwall), allowing them to gain expertise in field work and sampling; molecular laboratory work; and statistical analysis. The supervisory team will provide training in the ecology of the field system, metapopulation and metacommunity theory, molecular genetic methods, and data informatics and analysis. The student will also have access to broader training opportunities at both institutions. At the end of the project, the student will have accomplished their own piece of research, but also developed strong transferable skills so they can consider a range of employment opportunities, from academic, through to more applied and practical roles.

The ideal candidate will have an interest in testing ecological theory using field data from natural systems. They will enjoy carrying out field work, but also in processing samples in the lab using modern molecular methods. They will also be keen on applying the latest statistical approaches to their data.

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.

To apply please send your CV and a covering letter stating your motivation to work on this project to the main project supervisor Prof. James Bullock ([Email Address Removed]) by midnight 07/01/2018.

Funding Notes

This project is one of a number of proposed topics that are in competition for funding from the NERC GW4+ Doctoral Training Partnership http://nercgw4plus.ac.uk/. Commencing in autumn 2018 if successful.

Full studentships (fees and stipend) are only available to UK nationals and other EU nationals that have resided in the UK for three years prior to commencing the studentship. If you are a citizen of an EU member state you will eligible for a fees-only award, and must be able to show at interview that you can support yourself for the duration of the studentship at the RCUK level.

References

Gols, R., Wagenaar, R., Bukovinszky, T., van Dam, N.M., Dicke, M., Bullock, J.M. & Harvey, J.A. (2008) Genetic variation in defense chemistry in wild cabbages affects herbivores and their endoparasitoids. Ecology, 89, 1616-1626.
Harvey, J., van Dam, N., Raaijmakers, C., Bullock, J.M. & Gols, R. (2011) Tri-trophic effects of inter- and intra-population variation in defence chemistry of wild cabbage Brassica oleracea. Oecologia, 166, 421-431.
Newton, E., Bullock, J.M. & Hodgson, D. (2009) Bottom-up effects of glucosinolate variation on aphid colony dynamics in wild cabbage populations. Ecological Entomology, 34, 614-623.
Newton, E.L., Bullock, J.M. & Hodgson, D.J. (2009) Glucosinolate polymorphism in wild cabbage (Brassica oleracea) influences the structure of herbivore communities. Oecologia, 160, 63-76.



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