Fungal endophytes of Festuca rubra increase in frequency following long-term exclusion of rabbits

Plant-fungal endophyte interactions are common in nature and they can shape the ecology of plants. Vertically transmitted endophytes are hypothesized to serve as mutualists, protecting plants from herbivores. If this hypothesis is true then we expect endophytes to be most abundant in the presence of herbivores and least abundant in their absence, assuming endophytes incur a cost to their host. We tested this prediction by studying the effects of intense rabbit (Oryctolagus cuniculus) grazing on grass-endophyte interactions at Silwood Park, UK. We examined seeds of red fescue (Festuca rubra) collected from 15 natural populations that were protected from rabbits for 0.3 to 21 years. Contrary to our prediction, the mean proportion of seeds with endophytes increased 1.84x, from 0.45 to 0.83, following 21 years of rabbit exclusion. To better understand the mechanisms driving this increase in frequency, we conducted a fully factorial greenhouse experiment where we manipulated the presence/abs...