Fig. 4.

Natural selection builds worker co-expression to boost worker tractability. (A) The observed workers of a trait tend to co-express. The average absolute Pearson’s R of all worker pairs is shown for each of the 257 traits with at least 10 observed workers. The expectation is estimated by reshuffling the observed workers of all 257 traits while maintaining the worker number of each trait. Box-plots marking 50% of the data points near the median within the box and 90% of the data points near the median between the two horizontal lines are presented, with an inset showing the frequency distribution of the co-expression level of all worker pairs of the median trait C-124C. (B) The trait variance explained by each observed worker is small even for traits with only one, two, or three observed workers. (C) The number of observed workers is strongly correlated with the co-expression level of the 100 most probable workers (Spearman’s ρ = 0.76, n = 501, P < 10⁻¹⁶). (D) Fitness coupling underlies worker tractability. The relatedness to fitness of a trait is the Pearson’s R between trait value and cell growth rate. A larger absolute R means stronger fitness coupling, with -0.096 < R < 0.096 corresponding to a statistically insignificant range after controlling for multiple testing. Each dot represents a trait, and a total of 501 traits are included.