Highly diverse communities of endophytic fungi ― fungi that colonize plant tissues without causing symptoms of disease ― live cryptically in all higher plants ranging from mosses to flowering plants. While knowledge of the biodiversity and biogeography of endophytes is rapidly increasing, the mechanisms that maintain their diversity and control their dispersal among plants in natural ecosystems are widely unknown. Specifically the concerted functions of mutualistic and antagonistic plant-insect interactions on endophyte diversity and dispersal are little understood. In a comparative approach using myrmecophytes (ant-plants) and closely related non-myrmecophytic plant species, the function of defending ants as well as insect pollinators and herbivores on endophyte dispersal will be analyzed in a Peruvian lowland tropical rainforest. This study will be the first ever to examine the dispersal ecology of fungal endophytes among plants while considering the function of mutualistic and antagonistic insects in a natural ecosystem. Applying next generation sequencing of endophytes from plant and insect samples collected at the study site together with isolating living endophytes for morphological and molecular characterization will permit the novel analysis of environmental and evolutionary factors influencing the diversity and community composition of these cryptic organisms. This project will use state of the art techniques in molecular community ecology and dispersal modeling and will address important questions of wide relevance for general distribution mechanisms of fungal endophytes. The proposed research will be combined with high quality training in population genetic and phylogenetic methodology, provided by world leading experts in these areas.