Chondrocranial variation in chicken domestication.

The chondrocranium is a key structure of the skull, but our knowledge of its embryonic development is based mostly on investigations of few stages across taxa. Variation of chondrocranial features is known across species, but little is known about intraspecific variation, or its evolution in the context of domestication. Here, we investigated two specific structures of the chondrocranium in three windows of embryonic development. The anatomy of one of these structures was also compared among adult skulls of chickens and their wild ancestor (red junglefowl [RJF]). The proccesus tectalis and the prenasal process, along with the surrounding area of the orbitonasal foramina, presented variation throughout the ontogeny and in the adults. The processus tectalis showed distinct variation from the earliest stage studied to the adult. The numbers of orbitonasal foramina were also found to be variable in the ancestor and breeds studied. Furthermore, during early embryonic development, the prenasal process is similar across breeds and RJF, but later in embryonic development this structure presents variable states. The embryonic and adult variation found herein could be an example of intraspecific variation under domestication, resulting from different types of tissue interrelationship during development.