Fig. 3

Relative heritability of various collective-level traits to cell-level heritability for size. Here, we examine the heritability of four multicellular traits that depend on the size of their constituent cells, relative to cellular heritability for size. The relationship between the size of the cells within collectives and the multicellular trait are shown as insets. We consider three biologically significant traits with different functions mapping the size of cells within the collective onto collective phenotype. The heritability of collective size (a) and diameter (b) is always higher than cell-level heritability for size and is maximized when cellular developmental noise is greatest and among-collective environmental effects are smallest (lower right corner). We modeled swimming speed (c) based on the model of Solari et al. [26] for volvocine green algae. We also considered survival rate under predation as a logistic function of radius (d). Like a and b, collective-level heritability is highest relative to cell-level heritability when environmental heterogeneity is minimal. Pink contours denote relative heritability of 1. In these simulations, we consider 32 cell collectives grown for seven generations. The colormap denotes collective-level heritability divided by cell-level heritability for size across 1024 σ, σ′ combinations