| Popis: |
The history of life has involved several major evolutionary transitions that have each led to the emergence of a new individual. Examples of major transitions in individuality include the evolution of the eukaryotic cell, multicellular organisms and eusocial societies. In each of these events, previously independently replicating units (cells, individuals etc.) cooperate to form a new individual, which can then only replicate as a whole. For this to occur, conflict between individuals needs to be minimised, to allow maximising their inclusive fitness to be roughly equivalent to maximising group fitness. It has been predicted that the way in which social groups form should be key for eliminating conflict between individuals and promoting cooperation. In this thesis, I have focused on two major evolutionary transitions; the evolution of multicellularity and the evolution of symbiosis, and show that the mode of group formation (whether groups are parentoffspring associations or not) is crucial for understanding when and why major transitions occur. Firstly, I show that the major transition to obligate multicellularity has only occurred with clonal group formation (where cells remain together after division). Secondly, I use an experimental system to show that predation pressure may be key in promoting the formation of multicellular groups in algae. Finally, I show that the mode of group formation is also important in between-species transitions. I use the evolution of symbiosis to show that transmission route of symbionts and environmental factors, determine how cooperative symbionts will be towards their hosts. |
