Upper thermal tolerance (CTmax) of the selected lines measured at the last generation (F6) after acclimation at 24, 28, and 32 °C. The response is calculated as the mean difference in upper thermal tolerance (CTmax) relative to the Control lines. Large points and whiskers represent mean ±1 SE for each treatment (n = 120 individuals): Up-selected (orange triangles), Down-selected (blue squares), Acclimated Up-selected (red circles), and Control (green diamonds). Smaller translucent points represent means of each replicate line (n = 60 individuals). See SI Appendix, Fig. S3 for absolute CTmax values and model estimates.