Development of postcranial pneumaticity in the turkey (Meleagris gallopavo): insight from the forelimb skeleton

Postcranial skeletal pneumaticity is a phenomenon in birds in which epithelial extensions of the lung-air sac system aerate bones. Detailed development of this phenotype remains largely unknown. Here, we investigate changes in bone, soft tissue and air space volume in the developing humerus of turkeys using computed tomography and micro-computed tomography. Employing a two-phase approach, we first tracked humeral air space development in vivo in domesticated turkeys between week 10 (W10) and W18 post-hatch. In phase 2, we analysed air space and marrow volume change through the first 22 weeks of post-hatch development. Our results indicate that pneumatization of the humerus begins between W2 and W4 post-hatch, with air spaces expanding distally from the proximal humerus. Internal air space expands most rapidly between W7 and W9, with maximal volume reached at W15. Increased marrow growth occurs between W13 and W19, coincident with stabilization and a potential decline in relative air space volume. Our study highlights a dynamic relationship between bone, marrow and pneumatic epithelium, suggesting pneumaticity expression is likely impacted by both within-bone tissue growth dynamics and extrinsic factors related to forelimb function. This work provides the necessary gross anatomical framework for subsequent analyses of tissue-level and cellular mechanisms related to the pneumatization process.This article is part of the theme issue 'The biology of the avian respiratory system'.