In Saccharomyces cerevisiae, the FLO1 gene encodes flocculins that lead to formation of multicellular flocs, that offer protection to the constituent cells. Flo1p was found to preferentially bind to fellow cooperators compared to defectors lacking FLO1 expression, enriching cooperators within the flocs. Given this dual function in cooperation and kin recognition, FLO1 has been termed a “green beard gene”. Because of the heterophilic nature of the Flo1p bond however, we hypothesize that kin recognition is permissive and depends on the relative stability of the FLO1⁺/flo1⁻ versus FLO1⁺/FLO1⁺ detachment force F. We combine single-cell measurements of adhesion, individual cell-based simulations of cluster formation, and in vitro flocculation to study the impact of relative bond stability on the evolutionary stability of cooperation. We identify a trade-off between both aspects of the green beard mechanism, with reduced relative bond stability leading to increased kin recognition at the expense of cooperative benefits. We show that the fitness of FLO1 cooperators decreases as their frequency in the population increases, arising from the observed permissive character (F₊₋ = 0.5 F₊₊) of the Flo1p bond. Considering the costs associated with FLO1 expression, this asymmetric selection often results in a stable coexistence between cooperators and defectors.

在酿酒酵母中，FLO1基因编码絮凝蛋白，可导致多细胞絮凝物的形成，从而为组成细胞提供保护。研究发现，与缺乏FLO1表达的叛逃者相比，Flo1p 优先与其他合作者结合，从而丰富了絮凝物内的合作者。鉴于这种合作和亲属识别的双重功能，FLO1被称为“绿胡子基因”。然而，由于 Flo1p 键的异亲性，我们假设亲属识别是允许的，并且取决于 FLO1 + ^/ flo1 −^与FLO1 + ^/ FLO1 +^分离力F的相对稳定性。我们结合单细胞粘附测量、基于单个细胞的簇形成模拟和体外絮凝来研究相对键稳定性对合作进化稳定性的影响。我们确定了绿胡子机制的两个方面之间的权衡，相对债券稳定性的降低导致亲属认可度的增加，但以牺牲合作利益为代价。我们表明， FLO1合作者的适应性随着其在群体中的频率增加而降低，这是由于观察到的Flo1p 债券的宽容特征 ( F ₊₋  = 0.5  F _{++ ) 引起的。}考虑到与FLO1表达相关的成本，这种不对称选择通常会导致合作者和叛逃者之间稳定共存。