Asexual fungal endophytes and their grass hosts have attracted growing research interest as systems in which to examine the ecological and evolutionary consequences of maternally-inherited symbioses. The lion’s share of research for these endophytic symbioses has been focused on Neotyphodium endophytes in three introduced, agronomic grasses (but especially one, tall fescue) and many of the concepts about endophyte-host interactions has been developed from these agronomic grass systems. One concept is that because endophytes produced alkaloids, they act as defensive mutualists of their hosts against herbivores. Thus, endophyte infections should reduce herbivore abundances and richness. We used long term field observations and experiments, where endophyte infection, host genotype, and environmental factors were controlled, to test how Neotyphodium endophytes in two native wild grasses (Arizona fescue and sleepygrass) the associated arthropod communities.
In both grasses, endophyte infection increased herbivore abundances and species richness, contrary to conventional notions. Endophyte infection in these grasses reduced natural enemy (predators or parasites) abundances and richness. These results suggest that endophytes and their alkaloids make have stronger negative effects on natural enemies of herbivores than the herbivores themselves, thus creating enemy-reduced space on infected native plants. The outcome of asexual endophyte interactions was also contingent upon host and endophyte genotype and environmental factors, and varies with host ontogeny.