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Julien Varaldi
Maître de conférence universitaire - UCBL
phone: +33 (0)4 72 44 81 01
fax: +33 (0)4 72 43 13 88
"Biométrie et Biologie Évolutive"
UCB Lyon 1  - Bât. Grégor Mendel
43 bd du 11 novembre 1918
69622 VILLEURBANNE cedex
Building: Mendel 1er étage Office: 122

  • Présentation générale

    How a parasite moves from one host to the next is a central question in parasitology. One strategy of transmission that is especially intriguing is that of parasite manipulation, which occurs when a parasite modifies the behaviour of its host in a way that increases its own transmission. For instance, the protozoan Toxoplasma gondii decreases predator avoidance of its intermediate rodent host, thus increasing the chance for the parasite to reach its feline definitive host (Vyas et al. 2007). T. gondii is poorly specific and can infect non-hosts species, like humans, where it is also associated with several behavioural modifications (84% of the french population is infected). Although dozens of examples of parasite manipulation have been described, identification of the underlying molecular pathways involved in this process is scarce and essentially concerns macroparasites (Thomas et al. 2005). Unravelling the mechanisms of the behavioural manipulation is expected to bring insights into several basic biological processes underlying the behaviour of animals and its disorders (for instance cytopathology of virus infection can be linked to neurobehavioral disorders in humans). Insects are often infected with microparasites (essentially bacteria and virus) that deeply interfere with their reproductive biology. This trend appears to be especially true for insect parasitoids that live as parasites of other insects during their juvenile stages. The aim of the project is to unravel the molecular mechanisms allowing a virus infecting the parasitoid Leptopilina boulardi to force females to lay their eggs in close vicinity with those of other parasitoid females, ie in parasitoid hosts (Drosophila larvae) that have already been parasitized (an event called “superparasitism”). This behaviour allows the virus to jump from infected to uninfected parasitoids lineages and complements its imperfect vertical transmission (from mother to offspring) (Varaldi et al. 2003). Understanding the molecular determinants of this subtle behavioural alteration should shed light on manipulation processes in general and give insights in the molecular determinants involved in “superparasitism” behaviour which is observed in most parasitoid species. This last point is of peculiar interest since insect parasitoids are beneficial organisms in agrosystems (since they regulate the density of crop pests), and that “superparasitism” leads to “egg wastage” and thus decreases parasitoid efficiency.

    Thomas, Adamo & Moore (2005) Parasitic manipulation: where are we and where should we go? Behavioural processes. 68, 185-199.
    Varaldi J., Fouillet P., Ravallec M., Lòpez-Ferber M., Boulétreau M. & Fleury F (2003). Infectious behavior in a parasitoid. Science 302, 1930.
    Vyas A, Kim SK, Giacomini N, Boothroyd JC, Sapolsky RM. (2007) Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors. Proc Natl Acad Sci U S A.