Laryngotracheal and cervical muscular anatomy in the genus Uroplatus (Gekkota: Gekkonidae) in relation to distress call emission

The gekkonid Uroplatus exhibits many autapomorphic features. The laryngotracheal region has long been noted to display unusual characteristics, with a widely expanded and membrane-roofed anterior portion of the trachea being prominent among these. It has been proposed that this tracheal expansion serves as a reservoir for pressurised air that is explosively released and provides the energy for the loud distress calls released by these lizards. To determine whether this hypothesis is supported by associated anatomical features, we examined the laryngotracheal region in more detail, for 6 of 14 of the species within the genus, and compared the results to what is known of the laryngotracheal anatomy of Afro-Malagasy geckos. The muscles of the gular region, and the form and dimensions of the trachea, larynx and their adnexa, are described. Modifications of the gular muscles and their attachments render the larynx of Uroplatus more mobile in the oropharyngeal region, and in large-bodied taxa (U. lineatus, U. sikorae) the trachea exhibits the degree of expansion previously observed for U. fimbriatus. In these taxa the paired gular muscles fail to meet in the ventral midline and are, instead, bridged by fascial sheets. These modifications are consistent with ventral displacement of the anterior terminus of the trachea when charged with pressurised air, prior to the opening of the glottal valve and the release of a loud, harmonically-unstructured and explosive distress call. Such calls are likely directed at avian and mammalian predators to induce a startle response. The range of anatomical form of the laryngotracheal region exhibited within Uroplatus provides insights into the variation of laryngotracheal structure, such as incomplete tracheal rings and a conical trachea, which are exhibited by other Afro-Malagasy geckos.