Abstract
The capacity to discriminate self from non-self occurs throughout the Tree of Life, and is necessary for fundamental processes such as multicellular growth, detection of pathogens, and choice of mating partners. In Ascomycete fungi, the detection of conspecific non-self is achieved by the product of highly polymorphic loci known as het (heterokaryon incompatibility) genes. When two fungal individuals (colonies) meet, they may fuse vegetatively only if they are compatible at all of their het genes. In other words, the het genes are central to our concept of the fungal individual and its conspecific interactions. In this talk I will focus on a case study of the Ascomycete Podospora anserina, where we show that pleiotropic effects on sexual compatibility of some het genes can lead to reproductive isolation, and hence speciation. I will also briefly touch upon recent findings of lichen biology that emphasize a big gap in our knowledge of heterokaryon incompatibility.