The domestic yeast Saccharomyces cerevisiae, a model organism in genetic research, is surprisingly poorly understood outside the lab. In particular, researchers have struggled to explain genomic data suggesting that S. cerevisiae outcrosses regularly in the wild, given the apparent absence of natural environments favoring the species’ sexual dreproduction. Researchers at the University of Florence in collaboration with Leonardo Dapporto, a postdoctoral researcher at Butterfly Diversity & Evolution Lab, have now identified at least one place where outcrossing is occurring regularly in the wild: within wasp guts. The team’s findings were published in PNAS yesterday (January 18).

Earlier work had shown that both pure and hybrid strains of S. cerevisiae could survive the guts of hibernating Polistes dominula wasps, and that these wasps played an important role in moving yeasts between grapes in European wineries. But it was unclear whether the hibernating wasps were simply incubating diverse yeast strains or if they were in fact promoting sexual reproduction and hybridization among gut-dwelling yeast. 

To find out, scientists fed lab wasps five S. cerevisiae strains. The researchers then compared the proportion of outbred strains in the wasps’ guts following hibernation to the proportions in control populations grown either in sterilized wine must (pressed grapes) or in lab conditions that favor mating.  After two months of wasp hibernation, one-third of the gut’s yeast population was outcrossed (slightly greater than the proportion in wine must), confirming that yeast can indeed mate within the P. dominula digestive tract. After four months, outbred strains had increased to 90 percent of the population—greater than the percentage in even the most favorable lab-growing conditions.

Reference Article: Stefanini, I.; Dapporto, L.; Berná, L.; Polsinelli, M.; Turillazzi, S; and Cavalieri, D. (2016). Social wasps are a Saccharomyces mating nest. PNAS, doi:10.1073/pnas.1516453113, 2016.