Anatomy and mechanisms of vocal production in harvest mice.

Characterizing mechanisms of vocal production provides important insight into the ecology of acoustic divergence. In this study, we characterized production mechanisms of two types of vocalizations emitted by western harvest mice (Reithrodontomys megalotis), a species uniquely positioned to inform trait evolution because they are sister taxa to peromyscines (Peromyscus and Onychomys) that use vocal fold vibrations to produce long-distance calls but more ecologically and acoustically similar to baiomyines (Baiomys and Scotinomys) that employ a whistle mechanism. We found that long-distance calls (ca. 10 kHz) were produced by airflow-induced vocal fold vibrations, whereas high-frequency quavers used in close-distance social interactions (ca. 80 kHz) were generated by a whistle mechanism. Both production mechanisms were facilitated by a characteristic laryngeal morphology. Our findings indicate that the use of vocal fold vibrations for long-distance communication is widespread in reithrodontomyines (Onychomys, Peromyscus, Reithrodontomys) despite overlap in frequency content that characterizes baiomyine whistled vocalizations. The results illustrate how different production mechanisms shape acoustic variation in rodents and contribute to ecologically-relevant communication distances.