Environmental factors are more effective at explaining differences in tropical fungal endophyte communities than distance

Background/Question/Methods

Understanding the distribution of microbial organisms across diverse environments represents an exciting frontier in biogeography research. We sought to build on a previous study showing that elevation and rainfall are important factors influencing the distribution of communities of foliar fungal endophytes in leaves of Metrosideros polymorpha (Myrtaceae), a widespread endemic Hawaiian tree across a tropical landscape in Hawai’i. In this study, we sought to explicitly quantify the extent to which the spatial structuring we observed in fungal endophyte communities can be attributed to distance alone, as opposed to being a result of variation in environment. To do so, we quantified endophyte communities in ten trees at each of six additional sites, across which elevation and mean annual rainfall are held as constant as possible but distance is varied. To quantify the foliar endophytic fungal communities in leaves of Metrosideros at each of these sites, we relied on high-throughput pyrosequencing of the internal transcribed spacer 1 region, amplified from surface-sterilized, asymptomatic leaves of Metrosideros polymorpha, using fungal specific PCR primers.

Results/Conclusions

By sampling across a set of sites that are similar in elevation and mean annual rainfall, but range in pairwise distance from tens to hundreds of kilometers, we find that distance shapes community similarity to a comparatively smaller extent than environmental factors do across a heterogenous tropical landscape. These results reinforce the prior finding of the importance of elevation and rainfall in structuring foliar fungal endophyte communities within a single host across the scale of a landscape, and suggest the different spatial scales at which environmental factors and geographic distance each may be relevent for shaping the composition of these microbial communities.