An endophytic fungus reduces herbivory in its recently colonised grass host: a food-choice experiment on common voles, weeping alkaligrass and Epichloë typhina

Abstract

The interactions of endophytes with plants are believed to evolve over time from parasitic to mutualistic, and in the seed-transmitted fungal endophytes, these interactions are conventionally treated as mutualistic. The weeping alkaligrass Puccinellia distans has recently dispersed to new habitats in Europe, where it was colonised by the seed-transmitted fungus Epichloë typhina. The E. typhina-infected weeping alkaligrass has a fertility advantage over -uninfected plants, but this advantage is held only over shorter time scales. We assess the antiherbivore value of E. typhina in mature weeping alkaligrass against common voles Microtus arvalis, a herbivore naturally co-occurring with weeping alkaligrass. In two consecutive food-choice tests conducted in a lab, we examined feeding by naïve voles on E. typhina-infected (E+) and -uninfected grass (E−) originating from Central Europe. In the first test, all voles consumed comparable amounts of E+ biomass and E− biomass. In the subsequent test, the voles reduced their feeding rates by 57 %, but E+ food was avoided twice as frequently as E− food (75 vs. 33 % reduction). This result suggests that toxins produced by E. typhina repel herbivores soon after the first contact. We show that in addition to its direct fitness consequences, endophyte-mediated resistance to herbivory increases the fertility advantage of E. typhina-infected weeping alkaligrass. This effect can increase the ability of weeping alkaligrass to invade habitats with intense herbivory.