3 Results
3.1 Patterns of ITV in hypocotyl along latitudinal gradients
The first two PC axes (associated eigenvalues > 1) accounted for 83.6% of the total variation among all these traits, where the first axis (PC1) mainly reflected hypocotyl mass and size, and the second axis was primarily determined by the shape index (RTD; Fig. 2). PC1 (fresh weight, fresh length, maximum transverse diameter, and minimum transverse diameter) decreased significantly with increasing latitudinal gradients (R 2 = 0.42, P < 0.001). In addition, quadratic regression had a better explanation for their relationship (R 2 = 0.53, P< 0.001; Fig. 3A). Intriguingly, RTD did not show any significant correlation with latitude (P > 0.05; Fig. 3B).