Geometric Morphometric Analysis of Adult and Juvenile Turtle Shells: Directional Asymmetry and Fluctuating Asymmetry

Bilateral symmetry is quite common in animals, but in some cases, asymmetry can be altered by hereditary or developmental processes. Symmetry may be preserved, or asymmetry may increase as the developmental stages progress. This study applied geometric morphometric analyses at the juvenile and adult stages to investigate directional asymmetry and fluctuating asymmetry in turtle shells. In total, 71 turtle shells (46 adults, 25 juveniles) of Testudo hermanni boettgeri were used. These turtle shells were recorded using the Generalized Procrustes method to interpret developmental asymmetry. A covariance matrix was then applied, followed by principal component analysis. Analysis of Variance (ANOVA) was used to explain individual variation. The procedures were applied and interpreted separately to the carapace and plastron. Specific structures, such as the nuchal and neural plates, exhibited a narrower shape than the mean shape configuration in directional asymmetry. The epiplastron region showed significant enlargement in juveniles compared to adults, potentially linked to developmental growth. This study investigated fluctuating asymmetry (FA) and directional asymmetry (DA) in turtle shells by analyzing the carapace and plastron. Although wavy asymmetry was not statistically significant overall, localized shape differences between the edges of the coastal and neural plates of the carapace and the edges of the plastron were observed. The side effects showed statistical significance (p = 0.0005). Environmental or developmental factors may have influenced these differences. Directional asymmetry was statistically significant for the carapace and plastron, indicating consistent shape changes associated with developmental growth. This study revealed significant directional asymmetry in the carapace and plastron of Testudo hermanni boettgeri, reflecting consistent developmental trends.