Social insect intestines are mating nests for 

Irene Stefanini1, Leonardo Dapporto2, Luisa Berná3 , Mario Polsinelli4, Stefano Turillazzi4,5, Duccio Cavalieri1,3

1Centre for Research and Innovation, Fondazione Edmund Mach, 38010 San Michele all’Adige, Trento, Italy; 2Istituto Convenevole da Prato, Prato, Italy 3NEUROFARBA Department , University of Florence, Florence, Italy; 4Department of Biology, University of Florence, Florence, Italy; 5Centro di Servizi di Spettromeria di Massa, University of Florence, Italy

Sex can be a difficult task for motionless, dispersed organisms such as the yeast Saccharomyces cerevisiae. Albeit asexual reproduction prevails in nature, yeast relies on sex to generate new genetic assemblies. The last decade increased knowledge on the worldwide S. cerevisiae biodiversity significantly broadened the yeasts population genetics horizons. In particular, social insects, recently acknowledged as vectors and sinks of S. cerevisiae in the wild, guarantee a possible location for yeast mating fastening this way the evolution of the budding yeast. We found the S. cerevisiae strains isolated from the intestines of wild social insects as presenting an outcrossing rate higher than any other strain found in wild and human-related environments. We provide experimental evidence that Saccharomyces sensu stricto strains co-habiting the intestines of social insects can sexually reproduce, giving rise to inter- and intra-specific hybrids. This result, obtained in in vitro conditions (Polistes spp. and Apis mellifera), is mirrored by the identification and whole-genome sequencing of S. cerevisiaeXS. paradoxus and S. cerevisiaeXS. bayanus hybrids isolated from the wild V. crabro guts. The intestine of social insects, a restricted environment in which different S. cerevisiae strains can simultaneously reside, is identified as place in which the budding yeast can meet and mate, finally acting as yeasts mating nest and contributing in shaping the fungal evolutionary ecology.