Stable or plastic body shape? Emys orbicularis hatchlings-juveniles growth patterns under different ecological conditions.

To test if habitat could shape shell features of freshwater turtles starting from birth, we tested hatchlings of Emys orbicularis, randomly chosen from four clutches of the same locality, under two treatments, firm (pond habitat) vs running (river habitat) water regimes. Due to mortality at the beginning of the experiment, we finally considered only two clutches. Turtle shells were characterized at hatch and after one year of treatment by means of traditional and geometric morphometrics and phenotypic trajectories analysis were conducted on both types of data. Carapace growth was isometric both in proportion and shape, while plastron showed an allometric pattern: length increased more than width while the contour showed an expansion of the rear part and a compression of the front one. The hydrodynamic conditions during growth did not seem to affect the phenotypic trajectories of shell proportions nor those of plastron. On the contrary a significant effect was found on the phenotypic trajectory of carapace: the size component (but not the angle one) was positively influenced by the “pond” treatment, suggesting a different growth rate between the two environmental conditions. Hypotheses on possible ecological constraints derived from habitat conditions are presented and discussed.