A mechanistic model for the evolution of multicellularity

Abstract

Through a mechanistic approach we investigate the formation of aggregates of variable sizes, accounting mechanisms of aggregation, dissociation, death and reproduction. In our model, cells can produce two metabolites, but the simultaneous production of both metabolites is costly in terms of fitness. Thus, the formation of larger groups can favor the aggregates to evolve to a configuration where division of labor arises. It is assumed that the states of the cells in a group are those that maximizes organismal fitness. In the model it is considered that the groups can grow linearly, forming a chain, or compactly keeping a roughly spherical shape. Starting from a population consisting of single-celled organisms, we observe the formation of groups with variable sizes and usually much larger than two-cell aggregates. Natural selection can favor the formation of large groups, which allows the system to achieve new and larger fitness maxima.

Evolution of multicellularity and unicellularity in yeastS. cerevisiaeto study reversibility of evolutionary trajectories

“…Mathematical models have demonstrated key steps in the transition from unicellular form to multicellular clusters (Pfeiffer & Bonhoeffer, 2003, Ispolatov et al, 2012, Willensdorfer, 2009, Amado et al, 2017.…”

“…However, understanding the evolution of complex multicellular organisms from unicellular organisms is challenging, because the first steps in this process occurred in the deep past (16, 19). Mathematical models have demonstrated key steps involved in the transition from unicellular form to multicellular clusters (20–23). Experimentally, yeast Saccharomyces cerevisiae has been used for studying the origin of multicellularity in eukaryotes (24–32).…”

“…Mathematical models have demonstrated key steps involved in the transition from unicellular form to multicellular clusters (20)(21)(22)(23). Experimentally, yeast Saccharomyces cerevisiae has been used for studying the origin of multicellularity in eukaryotes (24)(25)(26)(27)(28)(29)(30)(31)(32).…”

A theoretical approach to the size-complexity rule

“…; Amado et al. ). Indeed, “staying together” also occurs and is particularly important at high values of stickiness, and in such situations “coming together” and “staying together” take place simultaneously.…”

“…At this point, nonzero rates of aggregation and dissociation are considered. Although they play an essential role, the remaining mechanisms are significant, and the outcomes clearly differ from simple models of aggregation and dissociation (Krapivsky et al 2010;Amado et al 2017). Indeed, "staying together" also occurs and is particularly important at high values of stickiness, and in such situations "coming together" and "staying together" take place simultaneously.…”