Division of Evolutionary Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
Department of Public Health and Primary Care, School of Medicine, Trinity College Dublin, Dublin, Republic of Ireland.
Evolution. 2023 Jun 29;77(7):1647-1658. doi: 10.1093/evolut/qpad076.
In haploid species, sexual reproduction by selfing lacks the common benefits from recombination and is indistinguishable from asexual reproduction at the genetic level. Nevertheless, the evolution of self-compatibility, known as homothallism in organisms with mating types, has occurred hundreds of times in fungi. Two main hypotheses have been proposed for the evolution of homothallism. First, that homothallism offers reproductive assurance, which is especially important when species have an obligatory sexual phase in their lifecycle. Second, that homothallism is associated with population-level compatibility, increasing the chance of outbreeding. Here, we test these hypotheses using the fission yeast Schizosaccharomyces pombe, which is homothallic by mating-type switching, leveraging natural variation for switching efficiency in this species. Combining empirical tests with cellular automaton simulations, we show that homothallism by switching increases mating success of switching genotypes, but does not affect population-level compatibility. Experiments show that outcrossing is actually reduced under homothallism. This reduction in outcrossing is explained by our simulations, which show that due to local mating, gametes that mated through intraclonal selfing are no longer available for outcrossing. Our results suggest that the recurrent evolution of haploid self-compatibility is likely driven by selection for mating assurance, not to increase the potential for outcrossing.
在单倍体物种中，自交的有性繁殖缺乏重组的常见好处，在遗传水平上与无性繁殖无法区分。然而，自交亲和性的进化，在具有交配型的生物中被称为同体交配，已经在真菌中发生了数百次。对于同体交配的进化，已经提出了两个主要假设。首先，同体交配提供了繁殖保障，这在物种的生命周期中具有强制性的有性阶段时尤为重要。其次，同体交配与种群水平的兼容性有关，增加了异交的机会。在这里，我们使用交配型转换的裂殖酵母 Schizosaccharomyces pombe 来检验这些假设，利用该物种中转换效率的自然变异来实现转换。通过结合经验测试和细胞自动机模拟，我们表明通过转换实现的同体交配会增加转换基因型的交配成功率，但不会影响种群水平的兼容性。实验表明，同体交配实际上会降低异交。我们的模拟表明，由于局部交配，通过克隆内自交交配的配子不再可用于异交，从而解释了异交的减少。我们的研究结果表明，单倍体自交亲和性的反复进化可能是由交配保障的选择驱动的，而不是为了增加异交的潜力。
