9520728 Martin Associations between fungal endophytes and grasses range from parasitic to mutualistic, and are ideal for studying the conditionality of interactions. Frequencies of infected plants in populations can increase over time; this is often cited as evidence that the interaction with seed-borne endophytes is a mutualism. The assumption is that relative fitnesses of infected and non-infected plants are constant. If relative fitnesses vary, the interaction between grasses and fungal endophytes may be delicately balanced, and shift from mutualism to parasitism depending upon environmental factors affecting costs and benefits. This project will test several factors that are hypothesized to affect the relative fitness of infected and non-infected plants. These include the roles of associated herbivore abundance, plant resources, and fungal endophyte strain in determining the balance of costs and benefits to the plant. Little is currently known about the extent of conditional outcomes in mutualisms, the mechanisms that determine outcomes, or the consequences of variation in outcome. Without this information it will be difficult to address important questions about the ecology of mutualisms. Since many plant species, including important agricultural crops, have associated fungal endophytes, understanding the mechanisms behind these mutualistic interactions also has considerable applied value.
