Metallicity gradient vs. stellar mass predicted by the respective best-fitting models when the metallicity gradients are measured in : NGC 7793 (black star), NGC 2403 (red triangle), NGC 300 (blue square), and M 33 (magenta diamond). The different line types represent observed metallicity gradients from different authors: dashed lines (Ho et al. 2015), dotted lines (Sánchez et al. 2014), and dash-dotted lines (Pilyugin et al. 2014).