Indonesian Komodo Dragons (Varanus komodensis) are clever,stealthy predators, possessing a mysteriously deadly bite. Some scientists blame pathogenic bacteria that reside in the lizard's mouths (due to their diet of rotting flesh) for the reptile's lethal bite. But Bryan Fry, a leading venom researcher in Australia, and 27 colleagues noted inconsistencies with this explanation and suggested an alternative hypothesis. They suspect that the lizards kill their prey by utilizing a `sophisticated combined-arsenal killing apparatus'. Essentially, there is more to the deadly bite than dirty mouths!
Fry's team had a unique opportunity to unravel the mystery of the endangered Komodo's deadly bite by accessing living specimens at the Singapore Zoo and comparing the dragons with equally vicious saltwater crocodiles(Crocodylus porosus).
Knowing that a predator's bite force typically determines prey size, Fry's team used magnetic resonance imaging (MRI) to analyze skull and jawbone and develop models to understand how Komodos bite. They determined that the dragon's bite force is only 39 N, despite their preference for large prey. That is not the tremendous force expected from a lethal bite, especially when the deadly croc, who also preys on large animals, bites with a force exceeding 250 N. The team also determined from the MRIs that the croc, like other biting predators, possesses a strong skull and jaw muscles to forcibly bite and resist struggling prey. Komodos, however, have lightweight skulls and weak jaw muscles.
So how do Komodo dragons generate their deadly bites? Fry's group exposed the Komodo's first secret: incredibly strong muscles behind the skull, perfect to resist their prey's pulling motions. The second secret is sharp, serrated teeth. Combined, these two characteristics result in the dragon's deadly `grip and rip' biting technique. However, the ferocity of the dragon's bite definitely hinges on a third component. Fry's team is the first to characterize the Komodo's venom gland, finding it to be the most complex ever described. Although the venom gland's six compartments contain copious quantities of venom, the dragon does not deliver its venom through fangs but through cavities distributed between the teeth that streak the venom through the wound as the reptile grips and rips its victim to death.
Next the team tested the toxic venom's effects on live rats and isolated blood vessels and found that it prevents blood clotting and decreases blood pressure, promoting excessive bleeding and shock. Just 3% of the venom carried in the Komodo's venom gland could immobilize a deer completely. This incredible potency must compensate for the Komodo's lack of an efficient venom delivery mechanism, such as fangs, which for snakes can deliver 50% of available venom into their prey.
The Komodo's killing apparatus is clearly multi-faceted. Venom is expensive to produce, and so if an animal allocates energy to make it, it must be effectively utilized. Fry's group also compared the Komodo dragon with fossils of its extinct close relative, the Australian Megalania lizard (V. priscus). They determined that 40,000 years ago, the Australian lizard was probably a combined-arsenal predator as well, suggesting venom may be an ancient killing strategy. Megalania was probably the largest venomous animal to have ever walked the planet, meaning Komodo dragons will have to settle for second place... just don't make me tell them!
