Morphological, radiographic, three-dimensional computed tomographic, and histological features of the primary upstroke and downstroke muscles and bones in the domestic duck (Anas platyrhynchos domesticus) and the cattle egret (Bubulcus ibis, Linnaeus, 1758), reflecting the evolutionary transition towards the irreversible flightlessness

The

Results of this study indicate that the bones and muscles of the pectoral girdle generally show specific morphological and structural changes reflective of the loss of prerequisites associated with flight behavior in domestic ducks due to domestication effects compared to cattle egrets.

Among the differences observed, radiographically, the distance between the paired clavicles was significantly wider (p < 0.05) in the domestic duck (mean ± SD 1.43 ± 0.23 cm) compared with the cattle egret (0.96 ± 0.13 cm). Unlike cattle egrets, there was no connection between the sternum and the hypocladium of furcula in domestic ducks. The scapula, clavicle, coracoid, sternum, and humerus were considerably longer in domestic ducks than in cattle egrets. The foramen triosseum appeared significantly (p < 0.01) wider in domestic ducks (0.7 ± 1.17 cm) compared to cattle egrets (0.49 ± 0.03 cm). Histologically, compared to cattle egrets, the muscle fibers in domestic ducks were loosely connected and contained fewer nuclei and perimysial/endomysial spaces. A higher myoglobin expression was evident in cattle egrets compared with domestic ducks. Conclusions: Results of this study indicate that the bones and muscles of the pectoral girdle generally show specific morphological and structural changes reflective of the loss of prerequisites associated with flight behavior in domestic ducks due to domestication effects compared to cattle egrets.