| Somatic recognition, or the ability to distinguish self from nonself, is found in a wide range organisms including vertebrates, colonial marine invertebrates, slime molds and filamentous fungi. Encounters between identical or related genotypes in these groups generally lead to fusion, and may result in the creation of physiologically large individuals. In contrast, encounters between individuals recognizing each other as nonself are usually followed by a rejection response that prevents or restricts cytoplasmic or nuclear exchange, allowing the persistence of each genotype as a discrete genetic and physiological individual.; This dissertation uses the oyster mushroom Pleurotus ostreatus as a model system to study the genetics and evolution of somatic recognition. The first part of the study involved setting up a series of backcrossed lines to isolate genes involved in somatic recognition. Three of the lines were found to be segregating at a single somatic recognition locus, the first description of such a locus in a basidiomycete. Pairings between isolates developed in this study suggested that three or more loci are probably involved in nonself recognition in Pleurotus.; The second part of the dissertation consists of a lab experiment that used sib-related genotypes developed in the first study to compare the growth on nutrient media of self, compatible nonself or incompatible nonself pairs. Incompatible interactions were associated with a significant reduction in growth relative to either self or compatible nonself pairs, demonstrating that recognizing and rejecting nonself can be costly. This suggests that factors not observed in this study must exist to explain the persistence of somatic rejection systems.; The last part of the dissertation presents the results of an analytical model exploring the behavior of a parasitic nucleus that reduces the fitness of host individuals, but has a transmission advantage because of its ability to invade compatible neighbors. Stable polymorphisms are shown to exist for a certain range of migration rates and relative fitness values. This result demonstrates the potential for such mutations to act as a selective force favoring the ability to recognize and reject nonself. |
