Comparison of embryonic development, from HH21 to HH40, between ostrich (Struthio camelus) and chicken (Gallus gallus)

• Published in: Developmental dynamics 2023-05, Vol.252 (5), p.668-681
• Main Authors: Bai, Shibin, Li, Shanshan, Li, Xiaoping, Zhu, Shiyu, Shan, Zhixin, Zhang, Junpeng, Irwin, David M., Zhang, Shuyi, Wang, Zhe
• Format: Article
• Language: English
• Subjects: Animals; Birds; Calcification; Cartilage; Chickens; Comparative studies; Developmental stages; Embryogenesis; Embryonic Development; limb skeleton; Morphology; Ossification; ostrich; Skeleton; stage; Struthio camelus; Struthioniformes - anatomy & histology; Toes
• ISSN: 1058-8388; 1097-0177
• DOI: 10.1002/dvdy.568

Background The chicken has been a representative model organism to study embryonic development in birds, however important differences exist among this class of species. As a representative of one of oldest existing clades of birds, the African ostrich (Struthio camelus), has the largest body among birds, and has two toes. Our purpose is to establish the corresponding stages in ostrich embryo development that match the well‐established HH system of the chicken to facilitate comparative studies between the ostrich and other birds to better understand differences in development. Results Here we describe in detail the middle period of embryonic development using microscopic images and skeletal staining. We found that clear morphological differentiation between the ostrich and the chicken begins at stage 26. Bird limb cartilage first form in stage 25, while the development of the limb skeletons differs after stage 31. Calcification of limb skeletons in the chicken was completed faster. The first and second toes of the ostrich disappear at stages 36 and 38, respectively. Conclusions This study should greatly aid ostrich‐related developmental and morphological research and provide a reference for studying the development and evolution of avian limb skeletons, including molecular research. Questions that can now be addressed include studies into the fusion of tarsometatarsal skeleton, ossification, and digit loss. Key Findings The stages of ostrich development are defined. Comparison of embryonic development between ostrich and chicken. Continuously record and describe limb bone development in the ostrich and chicken. Limb cartilage first forms in both species at stage 25. The unique degenerated first and second toes of the ostrich is completed by stages 36 and 38, respectively.