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

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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 Epichloe 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 naive 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.