A theoretical approach to the size-complexity rule

Abstract

The so-called size-complexity rule claims the existence of a positive correlation between organism size and number of cell types.In this spirit, here we address the relationship between organism size and number of potential tasks that can be performed.The modeling relies on the assumption that the states of the cells within the aggregates are such that the maximum fitness is realized, but also relies on the existence of tradeoffs among the distinct functions. For group sizes larger than the number of potential tasks, fitness maximization is attained when all cells in group specialize in a given task. Under this scenario, the number of potential tasks equals the number of cell types. We have found that the morphology and the topology of aggregates, as well as the developmental mode, strongly influence the dynamics of body formation. Particularly, it has been observed that more compact structures, such as sphere-like structures, are more likely to follow the claim of the size-complexity rule, whereas more fragile structures such as linear chains, which are more vulnerable to drastic changes due to division mechanisms, can, in a broad scenario, violate the size-complexity rule. K E Y W O R D S :Complexity, division of labor, evolutionary theory.

Topological constraints in early multicellularity favor reproductive division of labor

“…The origin of specialization has long been of interest to evolutionary biologists, ecologists, and economists. A large body of theory from these fields shows that specialization pays off only when it increases total productivity, compared to the case where each individual simply produces what they need ( Szathmáry and Smith, 1995 ; Smith and Szathmáry, 1997 ; Goldsby et al, 2012 ; Corning and Szathmáry, 2015 ; Hidalgo and Hausmann, 2009 ; Boza et al, 2014 ; Taborsky et al, 2016 ; Page et al, 2006 ; Rueffler et al, 2012 ; Szekely et al, 2013 ; Findlay, 2008 ; Amado et al, 2018 ). Certain types of trading arrangements maximize the benefits of specialization; highly reciprocal interactions, which facilitate exchange between complementary specialists, amplify cooperation ( Allen et al, 2017 ; Pavlogiannis et al, 2018 ).…”

“…When cells adhere through permanent bonds, sparse network-like bodies (i.e. filaments and trees) often result ( Amado et al, 2018 ). This mode of group formation is not only common today among simple multicellular organisms ( Umen, 2014 ; Claessen et al, 2014 ), but is the dominant mode of group formation in the lineages evolving complex multicellularity (i.e.…”

The evolution of germ-soma specialization under different genetic and environmental effects

“…Several additional points and connections are worth noting. First, as it was shown in Amado et al (2017Amado et al ( , 2018; Yanni et al (2020), the geometry of multicellular organisms can significantly influence the evolution of cell specialization. In our model, the group geometry is implicitly captured by different microenvironmental conditions experienced by cells of different prototypes (where a prototype is characterized by cells sharing the same vector of microenvironmental effects).…”

Ecological specialization under multidimensional tradeoffs

“…Tradeoff relationships are a critical factor in controlling the degree of ecological specialization in natural populations (Michod et al 2006). From an evolutionary perspective, this issue has been largely debated within the context of germ-soma differentiation (Michod et al 2006;Leslie et al 2017), and also discussed within the context of the evolution of multicellularity (Gavrilets 2010;Ispolatov et al 2012;Amado and Campos 2017;Amado et al 2018). A central feature about the tradeoffs is their structure (Jessup and Bohannan 2008;Saeki et al 2014).…”