A reproductive hierarchy controls mating fates among sibling yeast gametes
Mating strategies shape inbreeding, gene flow and genetic diversity, yet their outcomes remain challenging to quantify. In Saccharomyces, population-genomic models predict mating predominantly between sibling meiotic products, with rare selfing and outcrossing. Here we developed an integrated framework combining multicolor flow cytometry, time-resolved imaging and mathematical modelling to directly quantify mating across scales. Bulk measurements revealed coexisting strategies whose frequencies vary with density, genotype and environment. A minimal stochastic model uses these population-level patterns to infer probabilistic hierarchies among mating modes, which single-tetrad analyses independently support. These reveal divergent and interdependent reproductive trajectories among sibling gametes, with one pair typically mating first and reshaping opportunities for the others. Temporal heterogeneity in germination and mating further diversifies reproductive outcomes and shapes compatibility, as experimental synchronization overcomes temporal reproductive barriers, enabling hybridization. Together, reproductive strategy emerges from heterogeneous gamete fates, raising the possibility that sibling diversification constitutes reproductive bet-hedging.