VOCAL TRACT MORPHOLOGY DETERMINES SPECIES-SPECIFIC CUES IN LEMUR VOCALIZATIONS

Recent studies emphasize the importance of acoustic cues of species-specificity in primate vocal communication. The potential of vocal tract resonance in generating these cues is examined by anatomically correct vocal tract computational modeling. The oral vocal tract of lemurs is relatively flexible, but the nasal tract also plays an important role in their communicative system. In order to understand the functional morphology of lemurs’ vocal production, we analyzed the nasal tract anatomy of 6 genera. This contribution presents morphological studies of the nasal passages of the ring-tailed lemur (Lemur catta), the gentle lemurs (Hapalemur griseus ssp.), the greater bamboo lemur (Prolemur simus), the true lemurs (Eulemur spp.), the ruffed lemurs (Varecia spp.) and the sifakas (Propithecus spp.). The larynges and upper nasal airways of these taxa were investigated in combination with acoustic responses of computational models of their respective nasal tracts and with acoustic analyses of their vocalizations. Rubber casts were used to derive morphological measurements of the nasal cavities and area functions were calculated to generate anatomically correct computational models of the vocal tracts in order to investigate inter- and intra-specific variation and compare these outputs with formants measured from natural sounds. We observed distinctive formant characteristics between genera (P < 0,05). Results showed that congeneric taxa had remarkable similarities in tract size and shape and that differences in morphological features between lemur taxa determine acoustic characters of their vocalizations.