Alison Duncan: Competition and cooperation among parasites

Alison Duncan wonders why we want to interview her. The CNRS researcher welcomes us, somewhat incredulous, into her office at the Institute of Evolutionary Sciences in Montpellier. "With my name, you can imagine that I'm British," she says with an English accent. However, in 2022, she received the Mariano Gago Springboard Award for bilateral cooperation in research between France and Portugal, alongside Flore Zélé from the CNRS and Sara Magalhães, associate professor at the University of Lisbon. Their award-winning work focuses on competition and symbiosis among plant parasites. Alison Duncan is interested in bacterial, mite, and other harmful parasites, particularly the effect of competition between parasites on the virulence of attacks.

For pathogens, the generally accepted idea is that there is a trade-off between their level of virulence and their ability to spread widely. For example, a virus that is too virulent will kill its host and thus stop spreading. Conversely, a virus that is not virulent enough will be quickly eliminated. There would therefore seem to be a kind of optimum between the two. "Sara Magalhães and I wanted to verify this dynamic by observing the transmission of mites on bean leaves," explains Alison Duncan. Initially, the more virulent the mites are, the more they spread on the plant. But if the possibility of spreading stops, in other words if there are no more healthy leaves nearby, the relationship between virulence and spread is reversed. This is due to excessive competition between juveniles, which no longer have the resources necessary to reach adulthood.

The sex ratio of wasps

Having grown up in Cambridge, where academia is never far away, she is still surprised to have ended up in research. It was more a matter of chance than a career plan. "I loved my undergraduate internship at the University of Edinburgh, where I worked on the sex ratio of wasps. I was very intrigued by the fact that they don't always have a 50-50 sex ratio like most species, but can produce offspring that is largely female. It's a strange phenomenon, " says the researcher, sympathizing with the young student she once was. A position as a research engineer then became available in the lab where she was doing her internship in 2002. She seized the opportunity, which led her to a PhD a year later.

For her thesis, Alison Duncan is studying host-parasite interactions in Daphnia magna, small planktonic crustaceans. She observes how, when faced with a bacterial epidemic, certain specimens that are more sensitive to the parasite prevent mass mortality by favoring sexual reproduction.  These daphnia have two modes of reproduction: one sexual, with eggs that can remain dormant for several months before developing, and the other asexual (cloning) , which is immediate . "The daphnia observed laid eggs abundantly in the spring in response to the first infected individuals. Our hypothesis is that favoring asexual reproduction will allow their eggs to hatch later, once the epidemic has passed, " explains the researcher.

“My baptism of fire”

After earning her PhD in 2006, she completed three postdoctoral fellowships in Montpellier, first at the Mivegec unit ( Infectious Diseases and Vectors: Ecology, Genetics, Evolution, and Control) and then at the Institute of Evolutionary Sciences in Montpellier. Cambridge and Montpellier both have universities that are highly regarded in the field of evolutionary ecology. "And the southern heat doesn't hurt either, " she adds. She was awarded a grant for each of her postdoctoral positions, including a Marie Curie grant and a UM grant for international students. "I just met the criteria, " says the researcher modestly, who was awarded a position at the CNRS in 2014.

"I'm working on several other topics, including one that I'm particularly passionate about, but that would take a long time to explain, wouldn't it?" says Alison Duncan. The topic in question is the facilitation between parasites in attacking a host. It's a project with INRAE on tomato plants attacked by both mites and the tomato spotted wilt virus. If a plant is infected with the virus, researchers observe faster development of mites. "We can make two hypotheses that are not mutually exclusive," explains the biologist. " The virus triggers the release of free amino acids in the plant, making it easier for mites to eat. Or, weakened by the virus, the plant is less able to fight off mites."

The researcher also teaches. She first did so during two years as an assistant professor from 2011 to 2013. "It was my baptism of fire for French! I really enjoyed teaching and working with students, even though I was very worried about my language skills," recalls the researcher, who has continued to teach at the university. Having obtained her HDR (Habilitation à Diriger des Recherches, or accreditation to supervise research) in 2021, she is supervising two theses, one of which is in collaboration with Portugal.