Riparian plant litter is a major energy source for forested streams across the world and its decomposition has repercussions on nutrient cycling, food webs and ecosystem functioning. However, we know little about plant litter dynamics in tropical streams, even though the tropics occupy 40% of the Earth’s land surface. Here we investigated spatial and temporal (along a year cycle) patterns of litter inputs and storage in multiple streams of three tropical biomes in Brazil (Atlantic forest, Amazon forest and Cerrado savanna), predicting major differences among biomes in relation to temperature and precipitation regimes. Precipitation explained most of litter inputs and storage, which were generally higher in more humid biomes (litterfall: 384, 422 and 308 g m⁻² y⁻¹, storage: 55, 113 and 38 g m⁻², on average in Atlantic forest, Amazon and Cerrado, respectively). Temporal dynamics varied across biomes in relation to precipitation and temperature, with uniform litter inputs but seasonal storage in Atlantic forest streams, seasonal inputs in Amazon and Cerrado streams, and aseasonal storage in Amazon streams. Our findings suggest that litter dynamics vary greatly within the tropics, but point to the major role of precipitation, which contrasts with the main influence of temperature in temperate areas.

The natural biology of Saccharomyces cerevisiae , the best known unicellular model eukaryote, remains poorly documented and understood although recent progress has started to change this situation. Studies carried out recently in the Northern Hemisphere revealed the existence of wild populations associated with oak trees in North America, Asia, and in the Mediterranean region. However, in spite of these advances, the global distribution of natural populations of S. cerevisiae , especially in regions were oaks and other members of the Fagaceae are absent, is not well understood. Here we investigate the occurrence of S. cerevisiae in Brazil, a tropical region where oaks and other Fagaceae are absent. We report a candidate natural habitat of S. cerevisiae in South America and, using whole-genome data, we uncover new lineages that appear to have as closest relatives the wild populations found in North America and Japan. A population structure analysis revealed the penetration of the wine genotype into the wild Brazilian population, a first observation of the impact of domesticated microbe lineages on the genetic structure of wild populations. Unexpectedly, the Brazilian population shows conspicuous evidence of hybridization with an American population of Saccharomyces paradoxus . Introgressions from S. paradoxus were significantly enriched in genes encoding secondary active transmembrane transporters. We hypothesize that hybridization in tropical wild lineages may have facilitated the habitat transition accompanying the colonization of the tropical ecosystem.

Six novel yeast species, Starmerella camargoi f.a., sp. nov., Starmerella ilheusensis f.a., sp. nov., Starmerella litoralis f.a., Starmerella opuntiae f.a., sp. nov., sp. nov., Starmerella roubikii f.a., sp. nov. and Starmerella vitae f.a, sp. nov. are proposed to accommodate 19 isolates recovered from ephemeral flowers or bees in Brazil, Costa Rica and Belize. Sequence analysis of the ITS-5.8S region (when available) and the D1/D2 domains of the large subunit of the rRNA gene showed that the six novel yeasts are phylogenetically related to several species of the Starmerella clade. The type strains are Starmerella camargoi f.a., sp. nov. UFMG-CM-Y595T (=CBS 14130T; Mycobank number MB 822640), Starmerella ilheusensis f.a., sp. nov. UFMG-CM-Y596T (=CBS CBS14131T; MB 822641), Starmerella litoralis f.a., sp. nov. UFMG-CM-Y603T (=CBS14104T; MB 822642), Starmerella opuntiae f.a., sp. nov. UFMG-CM-Y286T (=CBS 13466T; MB 822643), Starmerella roubikii f.a., sp. nov. UWOPS 01–191.1 (=CBS 15148; MB 822645) and Starmerella vitae f.a., sp. nov. UWOPS 00–107.2 (=CBS 15147T; MB 822646). In addition, 25 species currently assigned to the genus Candida are reassigned formally to the genus Starmerella.

The study of microbe domestication has witnessed major advances that contribute to a better understanding of the emergence of artificially selected phenotypes and set the foundations of their rational improvement for biotechnology. Several features make Saccharomyces cerevisiae an ideal model for such a study, notably the availability of a catalogue of signatures of artificial selection and the extensive knowledge available on its biological processes. Here, we investigate with population and comparative genomics a set of strains used for cachaça fermentation, a Brazilian beverage based on the fermentation of sugar cane juice. We ask if the selective pressures posed by this fermentation have given rise to a domesticated lineage distinct from the ones already known, like wine, beer, bread, and sake yeasts. Our results show that cachaça yeasts derive from wine yeasts that have undergone an additional round of domestication, which we define as secondary domestication. As a consequence, cachaça strains combine features of wine yeasts, such as the presence of genes relevant for wine fermentation and advantageous gene inactivations, with features of beer yeasts like resistance to the effects of inhibitory compounds present in molasses. For other markers like those related to sulfite resistance and biotin metabolism our analyses revealed distributions more complex than previously reported that support the secondary domestication hypothesis. We propose a multilayered microbe domestication model encompassing not only transitions from wild to primarily domesticated populations, as in the case of wine yeasts, but also secondary domestications like those of cachaça yeasts.