Weizmann mass-mating experiment shows even yeast are choosy about partners

Researchers at the Weizmann Institute of Science reported in March 2026 that baker's yeast, a single-celled fungus, shows consistent preferences when choosing a mating partner. The study, published in Cell Reports, was led by Dr. Sivan Kaminski Strauss under the supervision of Professor Yitzhak Pilpel and Dr. Orna Dahan in the Department of Molecular Genetics, with collaborators from the University of Toronto and Côte d'Azur University in France.

To study mate choice at scale, the team mixed about ten million yeast cells drawn from roughly 100 natural strains and tracked which strains paired up with which. Some strains reliably avoided mating with certain others, a pattern that pointed to genuine preferences rather than chance encounters. The researchers then measured how well the resulting offspring grew under different conditions.

When the yeast had their preferred food, they tended to pair with partners that produced fitter offspring. When that food was missing, the genetic distance between the parents became the most important factor: offspring did better as parents became more genetically different, up to an optimal point, after which fitness declined again. From these data the team built a statistical model that predicts offspring fitness from the traits of the two parents and the environment.

Biologists have long debated whether selecting a mate is a basic feature of sexual reproduction or a refinement that appeared later in complex animals. Finding clear preferences in a single-celled organism suggests the behaviour may be very ancient. Yeast has long served as a model for genetics because its cells can reproduce both with and without a partner, which makes it possible to compare the two strategies directly in the lab.