Evolution of the number of Trojan asteroids (top plot) and the asymmetry ratio between the L₄ and L₅ swarms (bottom plot). The migration of Jupiter starts at t ~ 2.3 Myr and stops at t = 3 Myr, when the protoplanetary disc photoevaporates. The green shaded region represents the observed values of the Trojan asymmetry found by Grav et al. (2011), the yellow shaded region represents the observed values of the Trojan asymmetry found by Szabó et al. (2007) and the red line represents the asymmetry ratio estimated in Nakamura & Yoshida (2008). In this latter case the shaded region has not been overplotted to keep the figure readable, but the uncertainty is indicated in the legend.