Some reptiles such as the crocodile have armored skin. Based on their strength, they do not need to rely on chemical defense. Yet even small reptiles mostly seem to lack the ability to produce defensive compounds. There are only two lizards known that are toxic: the gila monster (Heloderma suspectum) and the beaded lizard (Heloderma horridum). They bite attackers and inject a protein cocktail via venom glands that end in the front teeth containing a hyaluronidase, a kallikrein, an arginine ester hydrolase, and a glycoprotein called gilatoxin. Recent cDNA analysis of goannas (Varanidae) suggests that these animals produce venoms themselves and do not rely on toxins produced by microorganisms as previously assumed. This finding suggests that toxin production evolved before diversification of reptiles to goannas and snakes.
In contrast to most other reptiles, many snakes produce highly active poisons. Those venoms mainly serve them to catch their prey using a poison fang to introduce the venom into the victim. However, such poisons can also act as powerful defense compounds. Consequently, only few animals attack venomous snakes. Many snake toxins are highly complex cocktails of hundreds or even thousands of peptides and proteins exhibiting, for example, neuro-receptor or ion-channel-blocking, protease, phospholipase, or hyarolonidase activity. For defense, snakes usually use their venom only as last resort preferring to escape, pretending death, or showing warning behavior, for example, the sound of the rattle of the rattlesnake. Some cobras are known to spit their venom as defensive reaction trying to avoid the dangerous direct contact with a predator. Many snakes also regurgitate or smear feces on themselves, causing both a deterring smell and taste.
The Japanese natricine snake (Rhabdophis tigrinus) possesses nuchal glands on their dorsal neck region that break open releasing a poison when the snake is attacked. The poison was recognized to contain toxic bufadienolides which the snake sequesters from ingested toads (36, see the previous section on amphibian defense).
Was this article helpful?