Behavior and morphological adaptations of reptiles (Proceedings)


Behavior and morphological adaptations of reptiles (Proceedings)

May 01, 2011

There are greater than 6500 species of extant reptiles with a wide variety of behaviors and structural morphologies designed to allow them to escape notice or fight off enemies, reproduce, obtain food and adapt to their environment. This lecture describes some commonly seen and some less commonly seen behaviors and morphological adaptations in reptiles. These behaviors and adaptations are normal for the particular species or group discussed but to the unfamiliar hobbyist or clinician may appear to be a sign of disease or trauma.

Defensive behaviors

Catalepsy, death feigning, tonic immobility

This category describes a condition or state of external unresponsiveness to stimulation. This can be seen as maintenance of a rigid posture or of a flaccid condition. This behavior occurs commonly in some groups of snakes (e.g. hognose snakes, False spitting cobras) and has been described in lizards and crocodilians.

Hognose snakes (Heterodon sp.) are well known for their complex death feigning behavior. When first disturbed hognose snakes will exhibit an elaborate bluff display consisting of an exaggerated S-coil, loud hissing and false strikes. The tail is often tightly coiled and can be elevated. If grasped or further harassed, these snakes will begin to writhe violently with the mouth hung limply open and often will excrete urates & feces. Violent writhing continues for a short time and then the snakes assumes an inverted, limp posture, usually with the mouth open and the tongue hanging out. If the snakes is turned over onto its ventrum, it will immediately turn back onto its dorsum. When the threat is removed, the hognose snake slowly rights itself and crawls away. Pseudoxenodontines, closely related to the hognose snakes, and false spitting cobras (Hemachatus sp.) are also well known for their elaborate death feigning behavior that closely resembles that of the hognose snakes. Assumption of a rigid posture that could be misinterpreted as an injury has been described in Trachyboa boulengeri and the bandy bandy (vermicllia anulata).

For lizards and crocodilians, chameleons in the genus Brookesia and leaf tailed geckos (Uroplatus sp) exhibit tonic immobility when threatened as does the microteiid, echinosaura horrida. Death feigning occurs in at least one teiid (Callopistis flavipunctatus), one Cordylid (Gerrhosaurus major) and three monitor species. Hatchling caiman crocodylus vocalize, bite and struggle on land but feign death if grasped under water.

The evolution of death feigning and tonic immobility may be related to removal of movement; a widespread class of stimuli among vertebrates, that elicits killing behavior by a predator. Reduction or elimination of the cues for killing might provide the potential prey animal with later opportunities for escape, especially from predators that transport whole, immobile prey to their young (e.g. raptors, canids). Alternative explanations involve the observation that many of the snakes that death feign eat frogs and toads, have enlarged adrenal glands, and at least one (Heterodon sp) exhibits bradycardia during death feigning. The author suggests that death feigning behavior is facilitated by typically high levels of circulating catecholamines and that it might represent a non-adaptive consequence of toad-eating. Evidence against this is that the death feigning response occurs repeatedly if a threat is rapidly presented and removed from a hognose snake and that the false spitting cobra remains alert and ready to bite while death feigning.

Squirting blood from the eyes and or nostrils

A number of species of horned lizards (Phrynosoma sp) and at least one species of boid (Tropidophis sp) squirt or exude blood from the eyes and or nostrils as a defensive mechanism. In horned lizards the ability to squirt blood is derived from modifications to the cephalic circulation. Restriction of blood flow from the head results in increased vascular pressure. Subsequent contraction, of the protrusure oculi muscles, ruptures capillaries in and around the eyes which causes a thin stream of blood to be ejected up to 2 meters. This defensive mechanism seems to be an especially effective deterrent to some mammalian predators (e.g. Canids).

Tail display

Tail displays as a defense mechanism are fairly common being seen in pipe snakes (Anilliidae), shield tailed snakes (Uropeltidae), ring necked snakes (Colubridae), burrowing pythons, sand boas and rubber boas (Boidae), coral snakes and shield nosed snakes (Elapidae) as well as a few lizard species. This behavior probably developed to divert a predators attack away from the vulnerable head to the more disposable tail.

The display varies between the different species and families but usually involves hiding the head beneath the body (coral snakes, shield tailed snakes) or within a coiled up body (sand boas, burrowing python). The tail is then waved around in the air, coiled tightly or moved in a manner that mimics a striking head (rubber boas). Many species (pipe snakes, coral snakes, ring necked snakes) have a brightly colored contrasting ventrum that is exposed when the tail is displayed. This can serve to startle the predator and give the snake a chance to escape; the tails of many of these individuals display scars from previous attacks that attest to the effectiveness of this defensive behavior. In many species, especially the coral snakes, the tail display is accompanied by writhing and cloacal discharge.

These displays can be misinterpreted as an animal in pain or possible neurologic disease.