The evolutionary origins of phagocytosis in microbial populations

Abstract: The emergence of the eukaryotic cell was one of the key events that paved the path to the vast variety of complex life visible all around us. A pivotal event in the process of eukaryogenesis was an endosymbiosis of two prokaryotic cells which in time resulted in the mitochondria. Phagocytosis, which is the process in which  larger cells envelope and digest smaller cells is one of the feasible explanations for how one cell came to be within another. It is common in eukaryotes, however, no contemporary examples of prokaryotes practicing phagocytosis exist. But phagocytosis had to evolve at some point, so how did it happen? This thesis gives an attempt to determine what conditions facilitate the evolution of phagocytosis. In this endeavour, we constructed chemostatic models for two different population structures where secondary consumers are subject to an invasion by a mutant with predatory capabilities. The different population structures are denoted as "competition" and "cross-feeding". By using random parameter sampling we show that the predator has a higher likelihood to invade in the cross-feeding environment. We also showed using adaptive dynamics that a mutant that is able to invade and replace its predecessor favours evolving towards a higher predation strategy in the cross-feeding case whereas in competition  such behaviour is less clear and a more balanced strategy seems preferable.