Postnatal development and form-function relationships of the vocal folds in California mice ( <i>Peromyscus californicus</i> )

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, and 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 in humans. This study investigates vocal fold structure and function in California mice (<i>Peromyscus californicus</i>) to inform a new model of vocal fold biomechanics. These mice can produce extremely high fundamental frequencies (<i>f</i>₀) 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 (<i>Mus musculus</i>) in size, shape, and α-smooth muscle actin expression. In addition, intrinsic laryngeal muscle myofibers doubled in diameter during the first 3 wk of life. We propose that the differentiated allometric growth of the larynx and vocal folds helps stabilize <i>f</i>₀ 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.<b>NEW & NOTEWORTHY</b> California mice produce high-pitched vocalizations through specialized vocal fold structures that grow and develop uniquely across life stages. Unlike common lab species, their vocal folds show distinct cellular traits that support vibration and durability. This study highlights key differences in tissue composition and fibroblast behavior, suggesting that species-specific vocal fold adaptations may be crucial for stable vocal function-offering new insights into voice biomechanics and potential models for human vocal health research.