Alison Duncan: Competition and Cooperation Among Parasites

Alison Duncan wonders why anyone would want to interview her. The CNRS researcher welcomes us, somewhat incredulously, into her office at the Institute of Evolutionary Sciences in Montpellier.“With a name like mine, you can probably guess I’m British,” she says with an English accent. Yet in 2022, she received the Mariano Gago Springboard Award for bilateral research cooperation between France and Portugal, alongside Flore Zélé of the CNRS and Sara Magalhães, an associate professor at the University of Lisbon. Their award-winning work focuses on competition and symbiosis among plant parasites. Alison Duncan is particularly interested in bacterial parasites, mites, and other pests—specifically, the effect of competition between parasites on the virulence of their attacks.

When it comes to pathogens, the generally accepted view is that there is a trade-off between their level of virulence and their ability to spread widely. A virus that is too virulent, for example, will stop spreading by killing its host. Conversely, a virus that is not virulent enough will be quickly eliminated. There is therefore a sort of optimal balance between the two. “With Sara Magalhães, we wanted to test this dynamic by observing mite transmission on bean leaves, ” explains Alison Duncan. Initially, the more virulent the mites are, the more they spread across the plant. But if the opportunity to spread ceases—in other words, if there are no more healthy leaves nearby—the relationship between virulence and spread reverses. The reason is excessive competition among juveniles, who no longer have the resources needed to reach adulthood.

The sex ratio of wasps

Having grown up in Cambridge, where the academic world is never far away, she is still surprised to have ended up in research. It’s a career path that owes more to chance than to a deliberate 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 are largely female. It’s a bit of a quirk, ” says the researcher, empathizing with the young student she once was. A research engineer position then opened up in the lab where she was doing her internship in 2002. She seized the opportunity, which would lead her to pursue a Ph.D. a year later.

For her thesis, Alison Duncan is studying host-parasite interactions using Daphnia magna, small planktonic crustaceans. She observes how, when faced with a bacterial outbreak, certain specimens that are more susceptible to the parasite prevent mass mortality by favoring sexual reproduction.  These daphnia actually 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 we 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 by fire”

After earning her Ph.D. 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 warmth doesn’t hurt, ” she adds. She was awarded a grant for each of her postdoctoral positions, including a Marie Curie Fellowship and a UM grant for international researchers. “I just barely met the criteria, ” explains the researcher modestly, who secured 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 while, wouldn’t it?” says Alison Duncan. The topic in question is how parasites cooperate to attack 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 mite development. “We can propose 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 defend itself against the mites.”

The researcher also teaches. She began as an assistant professor for two years, from 2011 to 2013. “That was my baptism by fire in 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 part-time at the university. Having earned her HDR in 2021, she is supervising two dissertations, one of which is in collaboration with Portugal.