Reptiles have a wide array of adaptations to help them survive. From camouflage to hiding places, these cold-blooded creatures have evolved strategies that set them apart from their prey.
Many reptile behaviors that could be misinterpreted as signs of illness or injury in pets are actually defensive displays. For example, many snakes and lizards display a hissing behavior to deter predators.
Tail Autonomy
Many lizards can drop their tail in response to a threat, a behavior known as caudal autotomy. They may do this to distract a predator or to escape from it. The detached tail wiggles vigorously, helping to draw the predator’s attention away from the lizard’s body and its vital organs.
The ability to shed a tail also helps prevent injury by reducing the force with which a predator can grip a lizard. However, caudal autotomy comes at a cost in terms of energy expenditure: the process requires the production of ovules, and individuals experience periods of reduced growth while their tails regenerate. It is especially costly for females, who must produce eggs while a new tail is forming (MD-L, personal observation).
It is currently believed that the ability to shed a tail evolved at least twice in lepidosaur reptiles: intravertebral autotomy, in which the caudal vertebrae break between inter-vertebral spaces at a point of weakness; and extravertebral autotomy, inwhich the shearing forces cause the tail to break apart along pre-formed fracture planes within the spinal column5.
An upcoming study will investigate whether regenerating a tail decreases the risk of predation in T. viridipunctatus, a species that exhibits a strong form of caudal autotomy. This work will provide valuable information about the costs and benefits of a caudal autotomy strategy, and further elucidate its maintenance as an evolutionarily beneficial adaptation to long-term predator-prey interactions.
Hiding Places
Reptiles have many ways to hide, such as blending into their surroundings (camouflage) or using their scales and skin to hide. They can also hide in a burrow or an artificial hiding place, like a box or log.
Some reptiles are good swimmers, but they don’t use their limbs to move through the water like amphibians do; they swim with lateral undulations of their body and tail. Crocodiles, aquatic lizards, and marine iguanas all swim this way. This form of locomotion is similar to that used by fish, and it may have been the mode of travel for some ancient mesosaurs and ichthyosaurs (order Archosauria).
Most reptiles don’t produce enough heat internally to keep their bodies warm; they rely on external sources of heat, such as sunlight, to regulate their body temperature. They can also absorb heat from other surfaces or objects, such as sand or bark.
When threatened, some lizards (particularly Asian rat snakes) and monitor species will flatten the caudal and cranial areas of their neck and heads to make themselves appear larger in a display called eversion. This behavior can be misinterpreted by novice pet owners as signs of neurologic disease or pain. Reptiles can also defend themselves by releasing a foul smell or writhing. Another defensive behavior is a cloacal display in which they empty their bladders and expel one or both hemipenes.
Tail Regeneration
Reptiles such as lizards, snakes and salamanders can regrow their tails after autotomy. This ability allows these animals to regain certain ecological functions that would otherwise be difficult, if not impossible.
For example, a lizard may shed its tail during a fight with a predator to distract the predator and give the animal the illusion that it is still struggling to escape. This behavior has been observed in several lizard species, including the squamate Plestiodon fasciatus and the diurnal sauropod Cordylosaurus subtessellatus. The detached tail will continue to wriggle, creating a deceptive sense of continued struggle and diverting predatory attention from the rest of the body and head.
The regrowth of the tail is a complex process that requires time and energy. The rate of tail regeneration varies depending on the species and environmental conditions. Lizards that live in areas with high terrestrial predator numbers have slower rates of tail regeneration than those living in less harsh environments.
In regenerated lizard tails, the initial stages of skeletal development are similar to those in embryonic lizards. First, wound epidermis forms over the stump and thickens to form an apical cap. Then, cellular proliferation occurs under the apical cap to form a blastema.
Then, proximal regenerated cartilage (CC) cells that contact original tail vertebrae become hypertrophic and express Alk Phos. The CCs also undergo endochondral ossification, which turns the chondrocytes into bones. In contrast, regenerated salamander tail CCs proliferate independently of blastema cells. This difference is likely due to different regulatory signals, which differ between lizard and salamander skeletons.
Adaptations for Land Life
A reptile’s scaly skin is more than just protective and beautiful—it’s also an incredible feat of evolution. It allows reptiles to thrive in a variety of harsh environments, from scorching deserts to freezing tundras. They use several tactics to regulate their body temperature and cope with extreme temperatures, including basking in the sun and hiding under ledges or trees.
Because they lack the ability to internally regulate their temperature like warm-blooded mammals, or to cool themselves by evaporating water like amphibians, reptiles are considered ectothermic, or cold-blooded. This means they rely on the environment and their behavior to maintain an optimal body temperature. When it’s hot, for example, they will shuttle between a cool shaded area and an open sunny spot to absorb heat. They can also hide under rocks or bark to keep cool, and most nocturnal reptiles will cover themselves with a layer of mud or dust to trap heat during the night (thigmothermy).
Reptiles are also able to conserve water by producing a more concentrated urine, so they can survive periods of drought. They have efficient excretory systems and specialized kidneys that help them maintain hydration on land. They can also retain moisture in their scaly skin by secreting a waxy substance called keratin.
Finally, most reptiles are oviparous and lay eggs with shells. This allows them to produce multiple broods each year, which is especially useful in climates where the weather can be unpredictable.