Postnatal Development and Form–Function Relationships of the Vocal Folds in California Mice ( Peromyscus californicus )

Most mammals produce vocal signals through vocal fold oscillations in the larynx, driven by airflow. Common species used as models (e.g., house mice, rats, rabbits) may not reflect the cellular specializations or developmental adaptations needed to support diverse vocal strategies or tissue repair under the mechanical stresses of phonation of humans. This study investigates vocal fold structure and function in California mice ( Peromyscus californicus) to inform a new model of vocal fold biomechanics. These mice can produce extremely high fundamental frequencies ( f₀) via airflow-induced vocal fold vibration and maintain this ability throughout life. We examined how vocal fold structure relates to function in California mice across three developmental stages. Vocal folds grow with negative allometry, undergoing changes in shape and composition. The epithelium is made up of 1–2 layers of squamous cells, and the lamina propria contains a fibrous matrix rich in collagen and hyaluronan but low in elastin. In vitro, California mouse vocal fold fibroblasts differed from those of house mice ( Mus musculus)—which primarily produce aerodynamic whistles—in size, shape, and α-smooth muscle actin (α-SMA) expression. Additionally, intrinsic laryngeal muscle myofibers doubled in diameter during the first three weeks of life. We propose that differentiated allometric growth of the larynx and vocal folds helps stabilize f₀ across development. A species-specific fibroblast phenotype may support vibration and enhance tissue resilience. These findings suggest that cellular adaptations in the vocal folds may play a larger role in species-specific vocal function and stability than previously recognized.