Foliar fungal endophytes live asymptomatically within the tissues of all plant phyla and are distributed worldwide across every terrestrial ecosystem that supports plant life. These cryptic fungal endosymbionts have been suggested as an indicator group for global fungal biodiversity due to their ubiquity, but their apparent ‘hyperdiversity’ has yet to be quantified (1) across the diversity of ecosystems in which they occur, (2) with analyses that explicitly account for host community structure and (3) with culture-independent methods (i.e., high-throughput sequencing) that capture rare and unculturable fungal species. To understand how foliar fungal endophyte diversity and composition vary as a function of climate and plant community structure, we surveyed foliar fungal endophyte communities from 21 temperate and tropical forests (5°N - 64°N) by intensively sampling all co-occurring plant host species within five 50 m2 quadrats per site during the summers of 2016 and 2017. We then sequenced the internal transcribed spacer 1 region on the Illumina MiSeq platform to directly characterize fungal community structure from host leaf tissue (n = 2,424 plant samples).
Results/Conclusions
Previous culture-dependent studies suggest foliar fungal endophytes are highly diverse in the tropics and follow the widely documented pattern in many plants and animals where species richness increases towards the equator - the latitudinal diversity gradient. However, our preliminary high-throughput data (6 of 21 sites) strongly suggest that foliar fungal endophyte diversity increases with increasing latitude, the opposite expectation of the latitudinal diversity gradient. Additionally, foliar fungal endophyte host specificity, quantified as the proportion of realized interactions in a given plant-fungal interaction network, increases with increasing latitude. I will discuss (1) how plant community structure and foliar fungal endophyte host specificity may contribute to these unexpected diversity patterns, (2) how contrasting patterns between previous studies and our preliminary data may be explained by detection technique, (3) the implications of foliar fungal endophyte diversity on our understanding of global fungal biodiversity and (4) outline future directions with phylogeographic and quantitative approaches.