Project Information AT A GLANCE
Project Title: SymbEvol: Symbiont-mediated coevolution in an insect host- parasitoid system
Project Objective: Many organisms are defended by microbial symbionts against parasites. The main objective of this project is to understand how these symbionts influence the coevolution of hosts and parasites, using a combination of mathematical modeling and experimental work on a study system of parasitoid wasps and their symbiont-protected aphid hosts.
Project Duration and Timing: 4 years, 2010 to 2013
Project Funding: Swiss National Science Foundation
the cost that the bacteria have to the aphids. All of these factors mean that this particular system is a lot more complex than the classic host-parasite interaction.” The Symbiont project has used both
theoretical modelling and empirical studies of the organisms in the lab to try and understand these interactions, and they have come up with some very intriguing results. “What we learn from models is that it is possible for the symbiont to take over from the host in responding to selection by the parasite,” says Vorburger. “When you look at the host’s genetic variation in these simulations, it looks rather static and one would assume that coevolution is not occurring. However, we have found that in these cases the really strong interaction is happening between the parasites and the bacteria, so this is where the battle is really occurring.” Another interesting find that resulted
from the empirical studies of the organisms was to do with the way in which the bacteria are able to move between host organisms. “We found a mechanism by which these bacteria are able to move laterally i.e. not just from mother to offspring,” says Vorburger. “When the wasps lay their eggs inside the aphids, their ovipositor can act much like a dirty needle, transporting bacteria from one aphid to the next one that is injected. Although the next aphid will usually die from having been parasitized, some of them survive, and they can then have the bacteria present inside of them that can be passed on to their offspring.”
www.projectsmagazine.eu.com Using an approach called experimental
evolution, in which evolution is observed in real-time in laboratory conditions, some
interesting findings were made
regarding the wasps’ own defenses to the bacteria. “What we wanted to find out was whether the wasps were able to become better at infecting the aphids that are protected by the bacteria, or whether they were totally helpless to this protection,” says Vorburger. “We were able to observe that they do become more effective at it, and very quickly, which confirmed our belief that the biological ‘arms race’ was occurring between the wasps and the bacteria, rather than with the aphids.” In the future Vorburger and his team
hope to try and work out the mechanisms by which these phenomena are occurring. “The next stage is to use genomic approaches to understand how the wasps are able to adapt against the bacteria. It could be something to do with enzymes, or possibly differing egg sizes, but we really do not know. It will only be with careful genetic studies that we will understand what is happening mechanistically.” Parasitoid wasps are commercially very
important as bio-control agents against the aphids, and so by understanding the coevolution system at play, it is possible that the wasps could be bred to be much more effective in this role. With food scarcity being the global problem that it is, the work being done in the SymbEvol project could be vital in ensuring that large amounts of crop harvests are not damaged.
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Project Partners: Eawag, Swiss Federal Institute of Aquatic Science & Technology
Main Contact:
Prof. Christoph Vorburger Christoph Vorburger is an evolutionary ecologist. The focus of his research is on the study of biological interactions that maintain genetic variation in natural populations. In particular, he is interested in insect host-parasitoid interactions and how these may be exploited for biological control of pest insects.
Contact: Tel: +41 58 765 5196 Email:
vorburgc@ethz.ch Web:
www.evec.ethz.ch
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