Global patterns of aquatic hyphomycetes biodiversity: mining digital repositories for morphology- and DNA-based data

Aquatic hyphomycetes (AHs) play key roles in freshwater ecosystems as decomposers of plant matter. Despite their importance and decades of studies, their distribution at the global scale remains poorly understood. Currently, large quantities of molecular data and morphological observations are being generated and stored in public repositories that provide unprecedented opportunities to investigate patterns of AHs biodiversity at broad spatial and environmental scales.

As part of the MoSTFun project (Monitoring Strategies and Tools to address knowledge gaps on aquatic Fungi biodiversity), we developed pipelines and protocols for standardised collection, integration, and reanalysis of aquatic fungal data from these digital sources. We integrated data from both morphology- and DNA-based observations, creating a comprehensive picture of the current knowledge of global AHs diversity and distribution. We used the resulting dataset to model global spatial patterns of AHs, identify potentially rare or undersampled species and regions, and developed pipelines and experiences to disentangle ecological patterns from sampling biases.

Preliminary results indicate that more than half of the currently known AHs species are represented in major public repositories such as GBIF, UNITE and GlobalFungi. The geographic coverage shows a majority of observations in temperate broadleaf and mixed forests with central Europe dominating the dataset but with important clusters also in China, the North-East of the USA and Australia. Data from tropical ecosystems, such as moist broadleaf forests, has greatly increased since the advent of metabarcoding techniques. These results support earlier observations that AHs are widely distributed in tropical and subtropical ecosystems, indicating that the focus on sampling from temperate regions is likely due to geographic bias and not a lack of species richness in the tropics.

Our findings thus identify currently understudied areas and ecosystems such as grasslands and savannas and showcase the benefit of integrating morphological and molecular observations to better characterise global AHs biodiversity. A refined global overview of AHs biodiversity and biogeography is crucial to develop conservation goals of this important fungal group, to identify rare and threatened species, understand their dispersal limitation, and improve our understanding of their role in maintaining functioning and resilient freshwater ecosystems.