Twin vocal folds as a novel evolutionary adaptation for vocal communications in lemurs - Scientific Reports
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Primates have varied vocal repertoires to communicate with conspecifics and sometimes other species. The larynx has a central role in vocal source generation, where a pair of vocal folds vibrates to modify the air flow. Here, we show that Madagascan lemurs have a unique additional pair of folds in the vestibular region, parallel to the vocal folds. The additional fold has a rigid body of a vocal muscle branch and it is covered by a stratified squamous epithelium, equal to those of the vocal fold. Such anatomical features support the hypothesis that it also vibrates in a manner like the vibrations that occur in the vocal folds. To examine the acoustic function of the two pairs of folds, we made a silicone compound model to demonstrate that they can simultaneously vibrate to lower the fundamental frequency and increase vocal efficiency. Similar acoustic effects are achieved using different features of the larynx for the other primates, e.g., by vibrating multiple sets of ventricular folds in several species and further by an evolutionary modification of enlarged larynx in howler monkeys. Our multidisciplinary approaches found that these functions were acquired through a unique evolutionary adaptation of the twin vocal folds in Madagascan lemurs.
  • @HaggunenonsOPM
    0•10 months ago

    Summary made by ChatGPT

    This scientific study provides a comprehensive analysis of a novel evolutionary adaptation in the vocal anatomy of Madagascar’s lemurs, specifically the discovery of twin vocal folds. Unlike other primates, lemurs possess an additional pair of vocal folds in the larynx, which the study proposes contributes to a more efficient vocalization mechanism by lowering the fundamental frequency and enhancing vocal efficiency. The research utilized an interdisciplinary approach, combining micro-computed tomography (μCT) scans for anatomical studies, histoanatomical analysis for tissue examination, and silicone compound model simulations to investigate the acoustic function of these twin vocal folds. This innovative methodological framework allowed for a detailed exploration of the unique vocal capabilities of lemurs, positing that these adaptations may have evolved to facilitate more effective communication within their environment.

    Discovery Details

    The key discovery is the presence of a second pair of vocal folds (vestibular vocal folds or VVFs) in lemurs, which are anatomically and functionally comparable to the primary vocal folds. This adaptation is proposed to enhance vocal efficiency and lower the fundamental frequency of vocalizations.

    Methodological Breakdown

    • μCT Scanning: Provided detailed anatomical insights into the laryngeal structure of lemurs and other primates for comparison.
    • Histoanatomical Analysis: Examined the tissue composition of the vocal folds, confirming their similarity to human vocal fold epithelium known for its resilience to mechanical stress.
    • Silicone Compound Model Simulation: Mimicked the physical dynamics of the twin vocal folds’ vibration, demonstrating their potential to alter vocalization properties significantly.

    Challenges and Opportunities

    The study acknowledges limitations such as the lack of direct in-vivo evidence of the VVFs’ function in lemurs. Future research opportunities include in-vivo studies to observe these vocal folds’ function directly and explore the evolutionary pathways that led to this unique adaptation.

    TLDR

    Madagascar’s lemurs possess a unique evolutionary adaptation: a second set of vocal folds that potentially enhances their vocal efficiency and lowers the fundamental frequency of their calls. This discovery was substantiated through detailed anatomical, tissue, and acoustic function analyses, paving the way for future explorations into primate vocal evolution.

    AI Thoughts

    This study not only sheds light on the evolutionary complexity and adaptability of primate vocal anatomy but also opens new avenues for interdisciplinary research in evolutionary biology, acoustics, and primate communication. Understanding such unique adaptations can offer insights into the evolutionary pressures and ecological demands that shape species-specific communication strategies, potentially influencing future research in bioacoustics, conservation efforts for endangered species, and the study of human speech evolution.