Anisogamy, the size difference between small male and large female gametes, is known to enable selection for sexual dimorphism and behavioral differences between sexes. Nevertheless, even isogamous species exhibit molecular asymmetries between mating types, which are known to ensure their self-incompatibility. Here, we show that different properties of the pheromones secreted by the MATa and MATα mating types of budding yeast lead to asymmetry in their behavioral responses during mating in mixed haploid populations, which resemble behavioral asymmetries between gametes in anisogamous organisms. MATa behaves as a random searcher that is stimulated in proportion to the fraction of MATα partner cells within the population, whereas MATα behaves as a short-range directional distance sensor. Mathematical modeling suggests that the observed asymmetric responses can enhance efficiency of mating and might thus provide a selective advantage. Our results demonstrate that the emergence of asymmetric mating behavior did not require anisogamy-based sexual selection.

Anisogamy，即小雄性配子和大雌性配子之间的大小差异，已知可以选择性别二态性和两性之间的行为差​​异。然而，即使是同种配偶的物种也表现出交配类型之间的分子不对称性，这可以确保它们的自我不相容性。在这里，我们展示了由MAT a 和MAT α 交配类型的出芽酵母分泌的信息素的不同特性导致它们在混合单倍体种群交配过程中的行为反应不对称，这类似于异配生物中配子之间的行为不对称。MAT a 表现为随机搜索器，其刺激与群体中MAT α 伙伴细胞的比例成比例，而MAT α 用作短程定向距离传感器。数学模型表明，观察到的不对称反应可以提高交配效率，因此可能提供选择性优势。我们的研究结果表明，不对称交配行为的出现不需要基于异配的性选择。