Social wasps are mating nests for yeasts

Saccharomyces cerevisiae is largely used in the industry of fermentations and has been the cradle and stage of genetics and molecular and cell biology. The recent availability of genome sequences of a large number of S. cerevisiae and S. paradoxus strains representing the widest known genetic, phenotypic and geographical diversity, renewed the interest in the use of these yeasts as models for evolution and ecology studies. Nevertheless, one of the still unanswered questions is whether genetically diverse yeasts mate and recombine in the wild. The yeasts outcrossing was estimated to occur only once every 105 mitotic divisions, thus confining their reproduction to mitosis and to occasional intra-ascus breeding. Yet the recent observation of unexpectedly high levels of genetic heterozygosity and prions diffusion called the rarity of outcrossing into question. To outbreed at least two conditions have to occur: i) different strains have to simultaneously inhabit the same environmental niche, ii) they have to face environmental oscillations favouring sporulation (natural yeasts are usually diploid) followed by germination. Social wasps have been shown to bear yeast cells all year long and feed on sources that are potentially inhabited by different Saccharomyces spp. strains, thus representing a potential incubator for different yeast cells to meet and mate. Here we show that the intestine of social wasps favours the mating of different yeast strains and species by providing a sequentiality of environmental conditions prompting the sporulation and germination of S. cerevisiae and making heterospecific mating the only option for S. paradoxus to survive. Our results open a new perspective introducing insects as unaware players in the evolution of Saccharomyces spp. yeasts. Saccharomyces spp. could prefer sexual reproduction to react to the environment changes occurring within the wasp intestine and in the continuous flux from the wasp to the environment and vice-versa.