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Inferring patterns and process in the global evolution of oak cynipid galls (NERC E4 DTP).


School of Biological Sciences

Prof G N Stone , Dr A Phillimore Thursday, January 07, 2021 Competition Funded PhD Project (Students Worldwide)

About the Project

For more information on this specific project and links to the E4 DTP application process, please visit
https://www.ed.ac.uk/e4-dtp/how-to-apply/our-projects?item=1346

Gall inducers are highly specialized herbivores that hijack the development of their host plant, causing it to produce a novel growth called a gall. Gall structures are under inducer control and can be seen as the ‘extended phenotypes’ of inducer genes. Galls are induced by a wide range of organisms including bacteria, fungi, nematodes, mites and over 30,000 species of insects. The tissues these organisms induce in their host plant provide all of its food, while outer tissues protect it from external conditions and (in some cases) from attack by natural enemies (see the reference below by Stone and Schönrogge 2003). While some gall inducers are mutualists of their host plant (such as legume root nodule bacteria, and pollinating fig wasps), most are parasites.

This project focuses on oak gall wasps, which induce some of the most diverse and structurally complex galls (to get a general idea, do a Google image search for ’oak gall wasps’). Female gall wasps lay an egg in meristematic tissue, and substances secreted by the developing larva cause the development of gall tissues (see references by Hearn et al 2019 and Cambier et al 2019 for theories on how this might happen). Around 1000 oak gallwasp species have been described, primarily from temperate North America and Eurasia, but recent work has revealed dramatic new diversity on tropical oaks and their relatives in Southeast Asia. A striking feature of gall wasp evolution is that similar gall structures have evolved repeatedly in different branches of the gall wasp evolutionary tree - for an example, see the reference below by Nicholls et al (2016). Some of these traits - such as nectaries that recruit ant guards, and coatings of sticky glue or spines - protect the gallwasp against attack by their main natural enemies - parasitoid wasps (see Bailey et al 2009, below). All parasitoids attack these galls by drilling through gall tissues using their ovipositor, and laying an egg in or on the gall wasp larva within. Any gall trait under gall wasp control that reduces the risk of attack by a parasitoid should spread by natural selection. Convergent evolution of effective defences also makes adaptive sense. However, other aspects of gall structure - such as colour patterns - as yet have no inferred function. Another feature of oak gall wasps is that they have two alternating generations, each of which always induces a very different type of gall.

This PhD will address the following questions:
1. Which gall traits have evolved convergently in different gall wasp lineages, what are their functions?
2. How often do gallwasp lineages switch between alternative gall structures through evolutionary time? Are some switches more common than others? Are switches reversible? Have gall structures become more complex through evolutionary time?
3. Do we see similar patterns in gall evolution in separate continental gall wasp faunas?
4. Do the structures of sexual and asexual generation galls in each species evolve independently, or in parallel?

This project is for a student who would like to learn how to reconstruct the evolution of biological traits - particularly those mediating interactions between species. You will explore techniques for characterisation of gall structures, and identify characters whose evolution you wish to reconstruct. You will learn how to use a range of analytical methods (primarily in R) to address the research questions above. Your analysis will make use of an existing 6-gene phylogeny for 350 gall wasp species, representing over 500 gall structures. There will be opportunities to add further taxa to this phylogeny through working with molecular post-docs in the Stone lab and, if circumstances allow, fieldwork in the US and/or China. The project will benefit from working alongside a fully funded NERC research project on the evolution of oak gall wasp communities, which includes project staff with expertise in taxonomy, molecular phylogenetics, and analysis.

The supervisors for this project combine expertise in community ecology and the evolution of insect-plant associations (Graham Stone) and analysis of macroecological and macroevolutionary patterns (Ally Phillimore).

IF YOU WOULD LIKE TO APPLY FOR THIS PROJECT, PLEASE GET IN TOUCH!

To find out more about what we do, visit our research web sites:
https://www.ed.ac.uk/profile/graham-stone
http://phillimore.bio.ed.ac.uk/AllyPhillimore
https://www.ceh.ac.uk/staff/karsten-sch%C3%B6nrogge

The School of Biological Sciences is committed to Equality & Diversity: https://www.ed.ac.uk/biology/equality-and-diversity

Funding Notes

Please see: View Website
for all application information including eligibility and funding.

UKRI has announced that international students will be eligible for all UKRI-funded postgraduate studentships from the start of the 2021/22 academic year and that they will be eligible for the full award - both the stipend to support living costs, and fees at research organisations UK rate (Home fees).

The University of Edinburgh will cover the difference between Home fees and International fees meaning that it will not be necessary for International applicants offered an E4 DTP project to find additional funding to cover the home/international fees gap.

References

All of the following can be found online using the DOI provided.

This paper is a good first read on theories about the adaptive significance of gall structures:

Stone GN & Schönrogge K (2003). The adaptive significance of insect gall morphology. Trends in Ecology and Evolution 18, 512-522.

The next 2 papers are examples of evolutionary analyses in gallwasps: Nicholls et al reconstructs the evolution of nectar secretion by galls, a neat example of a tetratrophic interaction (the gallwasp manipulates the plant to secrete nectar that attracts ants which repel parasitoids!). Bailey et al shows how gall traits influence which parasitoid enemies attack them.

Nicholls, J.A., Melika, G. and Stone G.N. (2016). Sweet tetra-trophic interactions: multiple evolutions of nectar secretion, a defensive extended phenotype in cynipid gallwasps. The American Naturalist. 189, 67-77. doi: 10.1086/689399.

Bailey R. et al. (2009). Host niches and defensive extended phenotypes structure parasitoid wasp communities. PLoS Biology, 7(8): e1000179. doi: 10.1371/journal.pbio.1000179

These papers look at how gall wasps might induce gall development.

Cambier, S., Ginis, O., Moreau, S.J.M., Gayral, P., Hearn, J., Stone, G.N., Giron, D., Huguet, E. and Drezen, J.-M. (2019). Gall wasp transcriptomes unravel potential effectors involved in molecular dialogues with oak and rose. Frontiers in Physiology, 10: 926. doi: 10.3389/fphys.2019.00926

Hearn, J., Blaxter, M., Schönrogge, K., Nieves-Aldrey, J.-L., Pujade-Villar, J., Shorthouse, J.D. & Stone, G.N. (2019). Genomic dissection of an extended phenotype: oak galling by a cynipid gall wasp. PLOS Genetics 15(11): e1008398. https://doi.org/10.1371/journal.pgen.1008398

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