Reptiles that are either fully aquatic or terrestrial burrowers have a limited capacity for thermoregulation. These species, as a rule, require that their body temperatures closely track environmental temperatures.
These thermal requirements are constrained by a range of lethal or ecological critical maximum and minimum body temperatures.
In order to attain optimum physiological body temperature it is necessary to gain access to a continuous supply of heat. This is an essential part of life for all reptiles.
Temperature Sensors
Even though reptiles generate 크레스티드게코 very little metabolic heat, they are able to maintain their internal body temperature at physiologically safe levels through behavioral thermoregulation. Reptiles bask in the sun to raise their body temperature and move into cooler environments (such as shade or burrows) to cool down. The hypothalamus, a key reptilian structure involved in thermoregulation, has been shown to receive thermal information from internal and peripheral thermosensors and integrate it for behavioral output. For example, early-stage turtle embryos are able to distinguish temperatures that are “warm” or “hot,” causing them to move toward the warm condition and away from the hot condition. This temperature gradient detection is triggered by thermal receptors, including the TRPV channels.
These channels are also activated by nociceptive stimuli, such as noxious chemicals, animal toxins, pungent compounds and low pH levels. The TRPV1 channel is the main thermal sensor in the reptile hypothalamus and is responsible for integrating input from internal and external temperature sensors.
Frogs are cold-blooded creatures that can also maintain their body temperature higher than the surrounding air temperature, but the exact mechanisms that they us 크레스티드게코 e to achieve this are still under investigation. Unlike snakes, which have special facial pits that detect the temperature of their surroundings, frogs use different behavioral strategies to regulate their body temperatures. Research has shown that the lateral-line organs in the platanna frog, Xenopus laevis, are sensitive to minute water turbulence and thermal gradients, but this is not enough to explain their ability to maintain body temperatures above ambient air temperatures.
Thermal Set Points
In the natural world, reptiles must spend a large portion of their time thermoregulating to center their body temperatures (Tb) within a range where metabolic functions are optimized. As a result, the thermal quality of their environment is a major determinant of how efficiently they can achieve and maintain their preferred Tb.
For example, if an animal needs to use a lot of locomotor energy for thermal regulation, their preferred Tb may not be achievable, or the process of maintaining it may be more costly than it should be. This could be a problem because the energy used for thermoregulation is unavailable for other activities such as foraging, defending territories or even just moving around in search of a suitable spot to rest.
As the climate warms, the frequency of events in which the lizard’s Tb is shifted away from its preferred range will likely increase. As a result, more of the lizard’s time will be spent on thermoregulation, and less on other ecologically important behaviors such as foraging or defending territory.
In this study, we assessed the effects of wind on the ability of a lizard to select a surface with the temperature it prefers. We also measured the time that a lizard spends in a retreat, which we interpreted as an indicator of the amount of time it is spending actively thermoregulating.
Evaporative Water Loss
Many reptiles lose heat by dumping water into their surroundings, changing the liquid into gas. This thermoregulation mechanism is similar to the way mammals sweat and pant to cool off. Thermoregulation is a vital function that all ectotherms must exhibit to avoid overheating.
Thermoregulatory behaviours in reptiles vary depending on species, habitat and the environmental conditions. For example, desert-dwelling reptiles such as the Sahara viper Cerastes bury their bodies in the sand with only the head poking out, which allows them to maintain an optimum body temperature even though temperatures of the air and soil vary dramatically. Other reptiles that live in rocky outcrops use a variety of strategies for thermoregulation such as climbing and resting in crevices to take in the surrounding air, or basking on rocks or logs to gain warmth from the sun.
Marine reptiles, such as the Leatherback sea turtle (Dermochelys coriacea), tend to spend most of their lives in the ocean and only leave it when they are laying eggs. These species don’t show the typical behavioural thermoregulatory behaviours that are observed in terrestrial reptiles when they leave the water and therefore aren’t considered to be capable of behavioural thermoregulation.
Generally, it is thought that thermoregulatory behaviour in reptiles evolved because the environments they live in are not thermally stable on a daily or seasonal basis. As a result, precise body temperatures can only be achieved in those environments where the heat flow patterns are consistent and easily accessible (low cost habitats).
Movement
In order to achieve operative body temperatures reptiles must be able to gain access to heat. This may be impeded by environmental factors (e.g., varying degrees of plant or cloud cover that limit the heat rays ability to penetrate). In addition, other reptilian behaviors can limit the ability of a reptile to reach its desired body temperature.
Reptiles use a combination of behaviors to warm and cool themselves in an attempt to maintain their bodies within a range where internal chemical processes work at their most efficient. Thermoregulation is a complex process with many variables that must be considered. This is particularly true for ectothermic reptiles that, unlike mammals, do not need to spend energy to maintain their body temperature.
As a result, reptiles must actively seek out the conditions best suited to their thermal state and body temperature. One method of doing this is through movement. For example, some frogs, toads, and caimans move in response to thermal gradients by hopping from rock to rock. During this activity the reptile’s skin heats up and cools down in sequence depending on its temperature.
Other reptiles may simply be stationary in response to thermal conditions. For instance, some sand-living reptiles such as the Sahara viper Cerastes, bury themselves in the sand with only their heads sticking out. This behavior allows the reptile to maintain a relatively stable body temperature despite a wide range of air and soil temperatures.