Data from: Experimental demonstration of the benefits of somatic fusion and the consequences for allorecognition

Allorecognition, the ability to distinguish ‘self’ from ‘non-self’ based on allelic differences at allorecognition loci, is common in all domains of life. Allorecognition restricts the opportunities for social parasitism, and is therefore crucial for the evolution of cooperation. However, the maintenance of allorecognition diversity provides a paradox. If allorecognition is costly relative to cooperation, common alleles will be favored. Thus, the cost of allorecognition may reduce the genetic variation upon which allorecognition crucially relies, a prediction now known as ‘Crozier's paradox’. We establish the relative costs of allorecognition, and their consequences for the short-term evolution of recognition labels theoretically predicted by Crozier. We use fusion among colonies of the fungus Neurospora crassa, regulated by highly variable allorecognition genes, as an experimental model system. We demonstrate that fusion among colonies is mutually beneficial, relative to absence of fusion upon allorecognition. This benefit is due not only to absence of mutual antagonism, which occurs upon allorecognition, but also to an increase in colony size per se. We then experimentally demonstrate that the benefit of fusion selects against allorecognition diversity, as predicted by Crozier. We discuss what maintains allorecognition diversity.

同种异体识别（Allorecognition）指基于同种异体识别基因座的等位基因差异区分“自身”与“非自身”的能力，广泛分布于所有生命域中。同种异体识别可抑制社会寄生现象的发生，因此对合作演化至关重要。然而，维持同种异体识别多样性却存在一个悖论：若同种异体识别相较于合作存在适应性成本，常见等位基因将受到正向选择。因此，同种异体识别的成本可能会削弱其赖以存在的遗传变异基础——这一预测如今被称为“克罗泽悖论（Crozier's paradox）”。本研究明确了同种异体识别的相对成本，以及其对克罗泽理论所预测的识别标记短期演化的影响。我们以受高度可变同种异体识别基因调控的粗糙脉孢菌（Neurospora crassa）的菌落融合过程作为实验模型系统。研究证实，相较于同种异体识别触发融合受阻的情况，菌落间的融合对双方均有益处。该益处不仅源于避免了同种异体识别引发的相互拮抗作用，还源自菌落自身规模的扩大。随后我们通过实验证实，融合带来的益处会对同种异体识别多样性产生负向选择压力，正如克罗泽的理论预测。最后我们讨论了何种机制维持了同种异体识别的多样性。