Reptiles use a variety of adaptations to live away from aquatic environments. These include scaly skin; dry, water-tight shells; internal fertilization of eggs; and lungs that enable them to venture far from aquatic habitats.
These changes allow them to obtain the nutrients they need from dry environments. Reptiles also conserve water by producing less urine in more concentrated forms.
Camouflage
Camouflage is a tactic that allows reptiles to blend in with their surroundings. It can be used to hide from predators or to distract them so that prey can escape. Some reptiles have fixed camouflage, while others can change it depending on the environment they are in. For example, sand-dwelling desert spiders can change their color to match the sand around them. Other reptiles can mimic other animals that are dangerous to predators, such as venomous snakes. This type of camouflage is called mimicry.
Reptiles can also use camouflage to hide in burrows, such as a cavern or a log. They can even camouflage their movement, such as when a group of zebras huddle together to look like a large mass to a predator.
The process of camouflage is gradual, and each individual reptile must survive long enough to pass on their genetic makeup for it to be replicated. Eventually, an animal with the right colors will be missed by predators and have a better chance of surviving.
Some animals can also combine camouflage with other defenses, such as aposematism and signaling. For example, a zebra’s pattern can divert the attention of a predator away from its vulnerable side, which makes it easier for the animal to escape. Likewise, some reptiles can shed their tails when grasped by a predator, which is a defense called autotomy. This adaptation is only found in a few species of lizard, but it can be quite effective.
Autotomy
Reptiles have a wide variety of behaviors and structural morphologies that allow them to hide from predators, defend themselves, reproduce, obtain food and adapt to their environment. To the untrained observer these behaviors and morphologies can seem like abnormal or pathological conditions. For example, a lizard’s tail might appear to be broken or cut off. In reality, this is a defensive behavior called autotomy (auto = self-, tomy = cutting) that allows lizards to detach their tails when threatened by predators. They then grow a new one in its place. This remarkable adaptation has evolved as a way to deter and evade natural predators.
The strategy works well; isolated tails of escaped geckos often turn up in the crops of birds of prey and in the stomachs of snakes and carnivorous mammals. It may also help distract a predator by diverting attention from the vulnerable head.
In a controlled experiment Jonathon Congdon and colleagues at Arizona State University exposed 30 western banded geckos with complete tails to spotted night snakes (Hypsiglena torquata). Although the snakes caught 19 of the lizards, 11 managed to escape by shedding their tails. The tails wriggled and distracted the predator, giving the lizards time to escape.
The ability to shed a body part can also be helpful in water where it is difficult to elude predators by lateral undulation of the body and tail. This movement, used by many crocodiles and aquatic lizards such as the marine iguana (Amblyrhynchus cristatus), mimics the swimming motion of a fish.
Thermoregulation
Thermoregulation is the ability of reptiles to regulate their body temperature by absorbing heat from their environment. This is a critical adaptation for cold-blooded reptiles, as they cannot produce their own internal heat. When reptiles become too cool, they can warm up by exposing themselves to the sun, hiding under bark or rocks and transferring heat from these objects to their bodies (thigmothermy). Some lizard species exhibit this behavior by raising one front leg while resting the opposite on a rock. They may also move from shade to sunlit areas to adjust their body temperatures throughout the day.
Other reptiles can warm themselves by soaking in rivers, lakes or seas, or by using evaporative cooling to remove excess heat from their bodies. Some lizards and snakes use burrows or other shelters to prevent excessive exposure to sunlight or wind, which can cause overheating. Some reptiles, such as pythons, can also shiver to generate their own body heat and help them warm up during the winter.
Animals have a wide variety of behaviors and structural morphologies to allow them to escape notice or fight off enemies, reproduce, obtain food and adapt to their environments. Ask students to identify the physical and behavioral characteristics of these examples. Point out that many of these traits may be seen as signs of disease or trauma by humans unfamiliar with reptiles, but that they are normal for the animals involved.
Mimicry
A variety of animals resemble one another to hide from predators, attract prey or blend in with their environment. Some of these mimicry systems are considered to be examples of coevolutionary arms races between predator and prey, between parasite and host or between predator and prey-host, but many are simply evolutionary convergent mimicry. Mimicry can be distinguished from crypticism by whether the traits being mimicked are signals or cues, and by whether the mimic advertises a benefit or cost to its receiver. This distinction is based on the idea that mimics must be able to distinguish their intended receiver from their model, and it highlights how clear criteria can help define different types of mimicry.
Aggressive mimicry occurs when a predator takes the “wolf in sheep’s clothing” approach and adopts the appearance of a harmless species in order to deceive its prey or host. It can also be found in predators that adopt the appearance of a benign herbivore to lure in prey or parasitoids that take advantage of their host’s defences to exploit the host population.
Similarly, Mullerian mimicry is a form of defensive mimicry whereby two or more species develop similar appearances to add additively to their protection from predators. This system can also be seen in a group of poisonous or noxious plants that share warning colours to alert predators to their presence.