A New Type of Infrared Sensitive Organ in the Python Aspidites sp.

by Guido Westhoff Shaun P. Collin

Pythons are well known to possess an infrared sense enabling them to perceive infrared radiation. It is believed that the infrared sense is mainly used to localise their warm blooded prey. The infrared sensitive organs are comprised of infrared sensitive thermoreceptors, which are embedded within specialised pits of the labial scales. Infrared signals are detected by these pits lined with thermoreceptors, which project to the cns via the trigeminal nerve and a specialised nucleus within the hindbrain (nucleus of the lateral descending trigeminal tract: nLTTD) to be relayed towards the midbrain and forebrain. The nLTTD is only found in infrared sensitive snakes. Aspidites sp. are the only members of the Pythoninae that do not possess labial pits. The lack of labial pits and thus the obvious lack of the infrared sense in Aspidites have been interpreted in the past either as a primitive character of this genus or as a secondarily loss due to the fact that these pythons feed on-cold blooded prey. We investigated a conspicuous U-shaped single pit located in the rostralia of Aspidites sp. which points downward in a resting specimen but clearly faces forward if the python raises its head. The rostral position and the overall shape of the pit allow frontal object localisation to be mediated by shadowing, where certain regions of the pit are differentially stimulated with regard to the position of objects in front of the animal. Scanning electron microscopy (SEM) has confirmed that the ultrastructure of the fundus of the pit resembles the fundus of labial pits in other pythons i.e. it possesses enlarged shingle like cells with micropits. Transmission electron microscopy (TEM) also reveals the presence of typical infrared thermoreceptors within the pit that are not found in other scales. Furthermore, the brain of Aspidites melanocephalus reveals a structure that can be regarded as a nLTTD. We propose that Aspidites clearly possesses an infrared sense and the unusual position of the single, downwardly-directed pit in the rostralia has evolved in response to its fossorial lifestyle i.e. to avoid damage to the pit from soil and debris. This arrangement is clearly different to the open labial pits of other pythons, which are directed laterally from the head. This work was partly supported by the Feodor-Lynen program of the Alexander von Humboldt Foundation.

Type: oral contribution

Theme: reptiles, snakes, morphology

Entity: Westhoff: Institute of Zoology University of Bonn Poppelsdorfer Schloss 53115 Bonn, GERMANY e-mail: Collin: Room A205 Ritchie Research Laboratories School of Biomedical Sciences The University of Queensland Brisbane, Queensland 4072 Australia e-mail: