Evolution in multicellular mitotic lineages

Sammanfattning: Many animals, and all plants and fungi, produce vegetative offspring, i.e. descendant individuals that originate from mitotic, rather than meiotic, cell lineages. Many animals, and all plants and fungi, produce vegetative offspring, i.e. descendant individuals that originate from mitotic, rather than meiotic, cell lineages. The overall purpose of this work is to increase our understanding of the evolutionary process in such lineages of asexual individuals. Specifically, I analyze cell dynamics and evolution in meristems. I investigate under what conditions mutant cell lineages in such meristems may have evolutionary significance. In the of absence of spatial constraints, e.g. in an unstratified shoot apical meristem, the probability of a mutant cell lineage, deleterious and advantageous rapidly reaching fixation is high. In the presence of spatial constraints, e.g. in a stratified shoot apical meristem, mutant lineages are efficiently purged. The occasional establishment of advantageous mutant lineages may give rise to long lived intraorganismal genetic heterogeneity. In multicellular mitotic lineages, e.g long lived and large modular organisms, such heterogeneity may play an important role in their ecology and evolution. The dynamics of the lineages in such heterogeneous organisms is a complex proces governed by selection presures and constraints at various levels of organization. One such xcomponent is the spatial arrangement of the lineages. I show that the fitness of the organism will strongly depend on, not only its size and proportion mutant modules, but also the spatial arrangement of the modules.