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Abstract Food webs govern interactions among organisms and drive energy fluxes within ecosystems. With an increasing appreciation for the role of symbiotic microbes in host metabolism and development, it is imperative to understand the extent to which microbes conform to, and potentially influence, canonical food web efficiencies and structures. Here, we investigate whether bacteria and their taxa and functional genes are compositionally nested within a simple model food web hierarchy, and the extent to which this is predicted by the trophic position of the host. Using shotgun and amplicon sequencing of discrete food web compartments within replicate tank bromeliads, we find that both taxonomy and function are compositionally nested and largely mirror the pyramid-shaped distribution of food webs. Further, nearly the entirety of bacterial taxa and functional genes associated with hosts are contained within host-independent environmental samples. Community composition of bacterial taxa did not significantly correlate with that of functional genes, indicating a high likelihood of functional redundancy. Whereas bacterial taxa were shaped by both location and trophic position of their host, functional genes were not spatially structured. Our work illustrates the advantages of applying food web ecology to predict patterns of overlapping microbiome composition among unrelated hosts and distinct habitats. Because bacterial symbionts are critical components of host metabolic potential, this result raises important questions about whether bacterial consortia are shaped by the same energetic constraints as hosts, and whether they play an active role in food web efficiency. 

Abstract Sphaerellopsisspecies are putative hyperparasites of rust fungi and may be promising biological control agents (BCA) of rust diseases. However, few detailed studies limit potential BCA development inSphaerellopsis. Here, we explored the biogeography, host-specificity, and species diversity ofSphaerellopsisand examined the early infection stage of one species, S. macroconidialis,to infer its trophic status. We randomly screened 5,621 rust specimens spanning 99 genera at the Arthur Fungarium for the presence ofSphaerellopsis. We identified 199 rust specimens infected withSphaerellopsisspecies on which we conducted morphological and multi-locus phylogenetic analyses. FiveSphaerellopsisspecies were recovered, infecting a total of 122 rust species in 18 genera from 34 countries.Sphaerellopsis melampsorinearumsp. nov. is described as a new species based on molecular phylogenetic data and morphological features of the sexual and asexual morphs.Sphaerellopsis paraphysatawas the most commonly encountered species, found on 77 rust specimens, followed bySphaerellopsis macroconidialison 56 andS. melampsorinearumon 55 examined specimens. The type species,Sphaerellopsis filum, was found on 12 rust specimens andSphaerellopsis hakeaeon a single specimen. We also recovered and documented for the first time, the sexual morph ofS. macroconidialis, from a specimen collected in Brazil. Our data indicate thatSphaerellopsisspecies are not host specific and furthermore that most species are cosmopolitan in distribution. However,S. paraphysatais more abundant in the tropics, andS. hakeaemay be restricted to Australia. Finally, we confirm the mycoparasitic strategy ofS. macroconidialisthroughin-vitrointeraction tests with the urediniospores ofPuccinia polysora. Shortly after germination, hyphae ofS. macroconidialisbegan growing along the germ tubes ofP. polysoraand coiling around them. After 12 days of co-cultivation, turgor loss was evident in the germ tubes ofP. polysora, and appressorium-like structures had formed on urediniospores. The interaction studies indicate thatSphaerellopsisspecies may be more effective as a BCA during the initial stages of rust establishment. 

Abstract Fungi are arguably the most diverse eukaryotic kingdom of organisms in terms of number of estimated species, trophic and life history strategies, and their functions in ecosystems. However, our knowledge of fungi is limited due to a distributional bias; the vast majority of available data on fungi have been compiled from non-tropical regions. Far less is known about fungi from tropical regions, with the bulk of these data being temporally limited surveys for fungal species diversity. Long-term studies (LTS), or repeated sampling from the same region over extended periods, are necessary to fully capture the extent of species diversity in a region, but LTS of fungi from tropical regions are almost non-existent. In this paper, we discuss the contributions of LTS of fungi in tropical regions to alpha diversity, ecological and functional diversity, biogeography, hypothesis testing, and conservation—with an emphasis on an ongoing tropical LTS in the Pakaraima Mountains of Guyana. We show how these contributions refine our understanding of Fungi. We also show that public data repositories such as NCBI, IUCN, and iNaturalist contain less information on tropical fungi compared to non-tropical fungi, and that these discrepancies are more pronounced in fungi than in plants and animals.