Higher fundamental frequency in bonobos is explained by larynx morphology

Area of Science:

• Primate communication
• Bioacoustics
• Evolutionary biology

Background:

• Acoustic signals provide insights into ecological and social selection pressures across species.
• The relationship between body size and acoustic parameters (e.g., fundamental frequency) is well-established in vertebrates.
• Deviations from acoustic allometry often involve adaptations in the larynx or vocal tract.

Purpose of the Study:

• To investigate the acoustic differences between bonobos (Pan paniscus) and chimpanzees (Pan troglodytes).
• To compare the vocalizations of these closely related human relatives in relation to their laryngeal morphology.
• To understand the evolutionary trajectory of communication in primates.

Main Methods:

• Comparative analysis of acoustic structures in bonobo and chimpanzee calls.
• Examination of laryngeal morphology, specifically vocal fold length.
• Correlation of acoustic parameters with morphological data.

Main Results:

• Bonobos and chimpanzees, despite overlapping body sizes, exhibit significant differences in fundamental frequency (f0).
• Bonobos possess shorter vocal fold lengths compared to chimpanzees.
• Shorter vocal fold length in bonobos directly accounts for their higher f0 calls.

Conclusions:

• The study reveals a rare instance of positive selection for signal diminution in primate vocalizations.
• Laryngeal morphology, specifically vocal fold length, is a key determinant of species-specific f0 differences in Pan species.
• These findings offer insights into the evolution of communication and its link to physical adaptations in human ancestors.