Theoretical study of marine macroalgal life cycle as an adaptation to seasonal environment

Seaweeds (marine macroalgae) show diversity of alternation of generations (life cycle). Especially notable is the difference between a heteromorphic life cycle and an isomorphic life cycle. In both heteromorphic and isomorphic life cycles, haploid and diploid generations alternate. Heteromorphic life cycle species show the large-sized algal body and the microscopic-sized body in their life cycle. In contrast, in isomorphic species, the haploid and diploid generations are similar in size and morphology. These different life cycles are observed in all three major divisions of macroalgae (Chlorophyta, Phaeophyta, and Rhodophyta), and are found in a variety of habitats. This suggests that heteromorphic and isomorphic life cycles have evolved many times in different species groups, and that they are likely to be adaptations to different environments. In spite of interests about the evolution of the life cycle as the adaptation to the environment, only a small number of prediction and verification studies have discussed the relationship between distributional pattern and life cycle strategy of macroalgae. In this thesis, I ask two questions: First, I discuss the ecology and distributional patterns of macroalgal life cycle focusing on the heteromorphic and isomorphic life cycle as adaptation to seasonal changing environment. Second, I discuss the evolutionary advantage of haploid versus diploid microbes in nutrient-poor environment.