Gular Pouch in Chameleons and its Function
Chamaeleo cf. roperi
Chamaeleo cf. roperi
Chamaeleo calcarifer
Rieppeleon brevicaudatus
Furcifer pardalis
Chamaeleo arabicus
Bradypodion damaranum
Trioceros q. quadricornis
Gular pouch in chameleons is an anatomical structure located in the chin are, below the mandible, which consists of an inflatable air sac (can be one or even more), attached to the breathing system via larynx and covered by skin and underlaying structures such as tendons and muscles and bones of the chin area, mainly building part of the hyioid apparatus.
It plays a function in few spectacular situations:
1. It can modify the form of chameleon body during thermoregulation (together with analogous pulmonary sacs.)
2. It can be inflated in case chameleon falls into water and help it floating to save life swimming to the shore.
3. It can be inflated in order to make the body appear bigger as an anti-predatory mechanism when facing a predator or being attacked.
4. It can be used for intraspecific communication, especially during imposing male-to-male or courtship and expose the often brightly and costrastly colored gular interstitial skin as a part of interspecific signalling.
5. Analogically to ad 4., it can be used for interspecific recognition, as the size, form (mainly silhouette) and color (especially of the interstitial skin) as these all are often species-specific.
6. It is taking part in the production of buzzing-sound and intense shaking of the body, especially in the head and neck areas (bio-tremor) produced by many chameleons using complex coordination of muscle activity of the hyoid apparatus and temporal pouch. It is playing part in anti-predatory mechanisms and intra-specific communication, it is not yet fully understand but intensively studied.
Images of inflated and fixed gular pouches of: (a) Chamaeleo calyptratus, (b) Chamaeleo dilepis, (c) Chamaeleo gracilis, (d) Furcifer oustaleti, (e) Furcifer verrucosus, and (f) Trioceros melleri. Scale bars are 2 mm for each panel, except for (a), which is 5 mm
Bioacoustics analysis of two representative biotremors in C. calyptratus. (A–C) Oscillogram (A), spectrogram (B) and power spectrum (C) of two vibratory signals of one of the experimental C. calyptratus. (D) Oscillogram of the first signal, enlarged to show the waveform of the vibration.
Muscle locations relative to the gular pouch in Chamaeleo calyptratus and a representative image of a gular pouch. (A) Representation of the M. levator scapulae (LS; pink), Mm. mandibulohyoideus (MH; red), M. sternohyoideus profundus (SP; purple), M. sternohyoideus superficialis (SS; blue) and gular pouch (gray) locations on an image of a skeletonized C. calyptratus. (B) Image (modified from Huskey et al., 2020) of an inflated gular pouch of a male C. calyptratus.
Gross anatomy of the throat of a male Jackson's chameleon, Trioceros jacksonii xantholophus (a and b) and a male veiled chameleon, Chamaeleo calyptratus (c and d). Scale bars are 1 cm. Ventral (e) and lateral (f) line diagrams depicting the location of the hyoid apparatus and tongue relative to the gular pouch in C. calyptratus. SP: M. sternohyoideus profundus; SS: M. sternohyoideus superficialis; MH: Mm. mandibulohyoideus; CBI: ceratobranchial I; CBII: ceratobranchial II; GP: gular pouch; EP: entoglossal process; T: tongue (comprised of the M. accelerator linguae and the M. hyoglossus)