Salvaudon, Lucie*; Héraudet, Virginie; Shykoff, Jacqui. Arabidopsis thaliana and the Robin Hood parasite. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-03. Click here to download the presentation on pdf format.

Are parasites always harmful to their hosts? By definition, indeed, but in a few cases and particular environments, the host experiences higher fitness in presence than in absence of its parasite. This observation of “mutualistic parasites” has received some theoretical attention and several explanations have been proposed. Some involved direct or indirect advantages given by the parasite, for instance the exclusion of other parasite species, others an adaptive tolerance of the host to parasite’s presence. However, clear demonstrations of any of these hypotheses are still scarce. Arabidopsis thaliana is naturally infected by a specific oomycete, Hyaloperonospora parasitica, which is usually not lethal but causes death of infected leaves. Inoculations of different host lines with various H. parasitica strains revealed that some combinations of host and parasite lead to higher host fitness in parasitized individuals. Only the most fecund, or “wealthiest” lines suffered fitness loss when infected, whereas “poorer” lines did not suffer from the infection or even increased their fitness. This apparent range of H. parasitica from parasitism to mutualism depending on host type, like Robin Hood, could be explained by different levels of tolerance in A. thaliana lines. One potential mechanism of plant tolerance to parasites, or herbivores, is a change in apical meristem activity and in resources allocation, leading to a modification of plant architecture and flowering pattern. We thus investigated this “Robin Hood” effect by testing whether it might be due to a differential change in life history traits of infected hosts over host lines and/or parasite strains.

Keywords: Arabidopsis thaliana, Hyaloperonospora parasitica, parasitism, mututalism, virulence, tolerance, life history traits, host genotype-by-parasite genotype interactions

*Institution: Université Paris Sud 11

Email: Lucie.Salvaudon@u-psud.fr