Sexually dimorphic laryngeal morphology in Rana pipiens

The sexually dimorphic vocal characteristics of Rana pipiens release calls suggest that there may be differences in the anatomical components of the larynx. The volumes of the arytenoid cartilage, surrounding muscle masses, vocal cords, supporting bronchial process, and the release-call amplitudes of six males and five females were measured in same-sized animals and sexual differences assessed. No qualitative differences in laryngeal morphology were observed, but all features measured except vocal cords were significantly larger in males. The implications of an increased laryngeal size are discussed in relation to differences previously observed in the vocalizations of this and other species and in relation to prior suggestions regarding the developmental basis of anuran sexual dimorphisms.