Fungal endophyte communities in galled oak leaves: Stability in leaves, divergence in galls

Gall-inducing Cynipid wasps create unique structures on oak leaves, yet their influence on fungal endophyte communities remains unclear. Using eDNA metabarcoding, we characterized fungal communities in ungalled Quercus douglasii leaves, leaves with galls, and the galls themselves. Fungal communities in galled and ungalled leaves were similar, suggesting gall formation does not substantially alter foliar endophytes. However, fungal communities within galls were distinct and species-specific. Urchin galls ( Cynips quercusechinus ) exhibited reduced fungal diversity and a dominant association with Cephaloascus fragrans , while saucer galls ( Feron gigas ) maintained greater overlap with leaf communities. These findings suggest that Cynipid galls specific to each wasp species can yield distinct fungal communities. As fungi influence plant health and insect interactions, understanding gall-associated fungal communities provides insight into microbial dynamics in oak ecosystems.