Foliar fungal symbionts in sympatric yellow monkeyflowers along elevation gradients in the Sierra Nevada

Microbial symbionts have the potential to contribute to host-plant's ecological and evolutionary success, especially in plants' adaptions to harsh environments, however their role has often been overlooked. Conversely, how host local adaptation (e.g., trait divergence across elevation) shapes the composition of associated microbial symbiont communities remains poorly understood. We explored how foliar endophytic fungi (FEF) abundance, richness, and community composition in three sympatric Monkeyflowers, an ecologically diverse group of flowering plants, change across elevation in the Sierra Nevada, CA, USA. We asked: Q1) Are there differences in leaf functional traits and FEF communities among sympatric <i>Mimulus</i> species populations at similar elevations? Q2) How do traits and FEF communities change across elevation within species? Q3) Are FEF richness, diversity and community composition correlated with leaf functional traits and/or elevation? Q4) How does FEF community composition differ with geographic distance within each species? We collected <i>M. guttatus</i>, <i>M. nasutus</i>, and <i>M.laciniatus</i> individuals from natural populations across the Sierra Nevada, measured leaf functional traits and used ITS sequencing to describe the leaf endophyte community. We found significant associations of FEF community composition with host species, and elevation, suggesting that these factors influence fungal community composition. Furthermore, FEF community dissimilarity was correlated with geographic distance indicating isolation by distance and limited dispersal of fungal endophytes. We detected the prevalence of <i>Vishniacozyma victoriae</i>, an endophyte found most commonly in Antarctica, across all Sierran <i>Mimulus</i> populations. The presence of <i>V. victoriae</i> could play a role in the adaptation of <i>Mimulus</i> to cold, high elevation environments. Our findings offer novel insights into the intricate interactions between fungal endophyte communities, plant traits, and elevation.