Trade-offs Drive the Evolution of Increased Complexity in Nascent Multicellular Digital Organisms

The transition to multicellularity was a major step in the evolution of large, complex life on Earth (Maynard Smith and Szathmáry 1995). Unlike other major evolutionary transitions, which have occurred only once (e.g., prokaryotes to eukaryotes), multicellularity has evolved multiple times in diverse lineages including archaea (Jahn et al. 2008), bacteria (Velicer and Vos 2009; Overmann 2010; Schirrmeister et al. 2011), and eukaryotes (Bonner 1998; King 2004; Grosberg and Strathmann 2007; Herron et al. 2013). Prior work suggests that the formation of simple clusters of cells, the first step in the transition to multicellularity, may be adaptive under a number of distinct ecological scenarios. For example, clusters may provide protection from predation (Kessin et al. 1996; Boraas et al. 1998), protection from environmental stress (Smukalla et al. 2008), or improved utilization of diffusible nutrients (Pfeiffer and Bonhoeffer 2003, Koschwanez et al. 2011; Koschwanez et al. 2013). Nevertheless, how and why nascent multicellular lineages evolve increased complexity remains a fundamental question in evolutionary biology. Progress has been impeded by a lack of experimental systems due to the fact that most nascent multicellular lineages have been lost to extinction.