Fungal microbiome diversity differs in live versus dead galls of baldcypress trees

Baldcypress trees (Taxodium distichum) provide stability to Gulf Coast swamps by decreasing erosion during floods and protecting inland areas from storm surge. By assessing the stress and/or parasitism levels of baldcypress trees we can monitor the stability of the swamps. Many plants’ defenses against stress and parasites may be based on microbiomes – the assemblage of microbes living on plant surfaces and in plant tissues. The baldcypress midges (Taxodiomyia cupressi and Taxodiomyia cupressiananassa) are common parasites of baldcypress trees. The purpose of this experiment was to see if there was a difference in the fungal abundance and diversity in living galls and dead galls. To test this, ~1500 baldcypress midge galls were collected from various sites around Southeastern Louisiana. The galls were left to overwinter outside and then recollected for emergence. Fungal cultures were sampled from galls that produced live midges and from a selection of galls that did not. The cultures of fungi were then sorted by morphological type and DNA was extracted for further identification. There was one prominent fungal strain from the dead galls across all the trees, whereas the galls that produced living midges had a greater diversity of fungal strains. This supported the hypothesis that the fungal microbiome inside the gall is related to the health of the midge. Further questions arise of whether the dominant fungal type within dead galls was associated with the midge’s death or invaded after the midge died. Future work should also explore whether the fungal microbiome inside of galls is generated from plant-associated symbiont communities or is inoculated by the egg-injecting female midges. Whether gall microbiome diversity benefits the plant, the parasite, or both remains an open question.