Geometric Morphometric Analysis of Sexual Dimorphism and Allometric Growth in the Skull of the Japanese Grass Lizard,Takydromus tachydromoides(Reptilia: Lacertidae)

We investigated sexual size dimorphism (SSD), sexual shape dimorphism (SShD), and allometric growth in the skull of Takydromus tachydromoides using geometric morphometries. We analyzed 40 landmarks on the skull from dorsal, ventral, and lateral views. As a result, significant sexual dimorphisms were recognized in both size and shape of the skull. The analysis of SSD revealed that adult males have larger skull relative to the snout-vent length, and the analysis of SShD indicated that adult males have larger jaw muscle adductor chambers than adult females. Moreover, various allometric shape changes in both sexes were visualized by the thin plate splines. However, only subtle sexual differences in allometric shape changes were observed. The skull size and shape of this species may be influenced by phylogenetic constraints and only weakly driven by sexual selection.