Fig. 3.

Shape parameter estimates of the beneficial tail of the distribution of synonymous effects. In all environments, the estimated shape parameter of the tail is positive, which indicates that the distribution of synonymous effects belongs to the Fréchet domain (i.e., that it can be characterized by a heavy-tailed distribution). This implies the presence of many nearly-neutral and few larger-effect mutations. The shape parameter was estimated using the tail shape estimator from empiricIST using the information of 1000 samples from the posterior distribution. Environmental conditions are indicated as the combination of temperature (25 °C, 30 °C, and 36 °C) or (25, 30, and 36 °C) and salinity (N = normal and S = high salinity)