The Evolution Of Bird Vocalization

The origin of novel traits—those that are not direct modifications of a pre-existing ancestral structure—is a fundamental problem in evolutionary biology, the evolutionary and developmental origins of the syrinx being a fascinating example. Located at the tracheobronchial junction, the syrinx is responsible for avian vocalization, but it is unclear whether avian vocal folds are homologous (similar in position, structure, and evolutionary origin) to the laryngeal vocal folds in other tetrapods, or whether it evolved convergently. For this study, the researchers identified a core developmental process involved in avian vocal fold formation and inferred the morphology of the syrinx of the ancestor of modern birds. They found that this ancestral syrinx had paired sound sources induced by a conserved developmental pathway and show that shifts in these signals correlate with syringeal diversification. The paper demonstrates that, despite being derived from different developmental tissues, vocal folds in the syrinx and larynx have similar tissue composition and are established through a strikingly similar developmental process, indicating that the origin of vocal folds in the avian syrinx was facilitated by co-option of an ancestral developmental program.
January 26. 2024