Combined CT and Rodopas Casting Assessment of Postural Variations in Lung Morphology of European Pond Turtles (Emys orbicularis).

Abstract

Respiratory morphology in chelonians exhibits unique adaptations compared to mammals, with multicameral lungs and large terminal chambers. This study combined computed tomography (CT) imaging and Rodopas-casting to assess structural and volumetric changes in the lungs of adult male European pond turtles (Emys orbicularis) between extended and flexed postural states of the head, neck, and limbs. Five turtles (550 ± 10.22 g) were evaluated under anaesthesia. CT scans quantified lung dimensions, volume, parenchymal thickness, and percentage coelomic occupancy, while Rodopas casts provided detailed bronchial architecture. CT imaging revealed bilateral wedge-shaped lungs positioned dorsally in the coelomic cavity, with the trachea entering from the right side and bifurcating into a longer left and shorter right bronchus. Each lung contained three lateral and four medial secondary bronchi, terminating in sac-like chambers, plus a large caudal terminal chamber. Lateral chambers were larger than medial ones; tertiary bronchi were denser in cranial lung regions. Casting confirmed bronchial branching but showed smaller terminal sac volume than CT, likely due to post-mortem differences. Morphometric analysis showed no significant differences in lung length or height between sides or postures. Cranial lung width decreased significantly in the flexed state (p < 0.05), while overall lung volume dropped markedly from 29.93 ± 0.33 cm³ (left) and 29.77 ± 0.33 cm³ (right) in extension to 23.41 ± 0.33 cm³ and 23.31 ± 0.32 cm³ in flexion (p < 0.001). Caudal parenchymal thickness was significantly reduced in flexed posture (p < 0.05). Coelomic cavity occupancy decreased from 43.06% ± 0.44% to 34.10% ± 0.47% (p < 0.001). These findings demonstrate that E. orbicularis lungs maintain overall shape during postural changes but undergo substantial cranial width and volume reduction with caudal parenchymal thinning. Differences between CT and casting highlight the complementary value of both techniques, with CT capturing functional, in vivo configurations and casting revealing intricate bronchial anatomy. The data provide new insights into respiratory adaptation and volumetric modulation in semi-aquatic chelonians, with relevance for comparative anatomy, evolutionary biology, and clinical imaging applications.