Wasp intestinal cues drive yeast toward outbreeding strategies.

Saccharomyces cerevisiae relies on social wasps (e.g. Vespa crabro, Polistes spp.) for dispersal and genetic mixing. Unlike most natural environments, wasp intestines provide conditions that support yeast survival, sporulation, spore germination, and mating. This study explores the mechanisms at the basis of this process by examining the wasp gut environment and yeast responses. Molecular analyses based on yeast deletion collection and transcriptomics showed that yeast sporulates in the crop, spores germinate in the gut, and cells ferment in the gut. The crop and gut differ chemically: the gut has more sugars, a higher pH, and (in workers) greater viscosity. In vitro tests confirmed yeast survival in both environments, with faster germination in gut-like conditions. Computational models based on these physicochemical traits matched the experimental results. The data obtained provide fundamental insights into yeast progression towards mating within wasps' intestines and suggest a possible relation between yeast alcoholic fermentation and wasps' alcohol tolerance, thereby enhancing our understanding of the S. cerevisiae-social wasp association.