ECTOTHERMY IN REPTILES

ECTOTHERMY IN REPTILES

¹Sumit Kumar Patel, ¹Somesh Singh and ²Amit Kumar Singh

¹School of Wildlife Forensic and Health

²Department of Veterinary Medicine

College of Veterinary Science and A.H., NDVSU, Jabalpur (M.P.)

Email of corresponding author- smtptl29@gmail.com

Introduction:

The word ‘reptile’ is a Latin word which means “one who creeps”. Reptiles are defined as a vertebrate animal of a class Reptilia. The major groups of living reptiles include- the turtles (order Testudines), tuatara (order Rhynchocephalia), lizards and snakes (order Squamata) and crocodiles (order crocodylia).

Reptiles are vertebrate creatures that either have four limbs or, like snakes, the descended from four-limbed ancestors. Snakes, lizards, and turtles have a three chambered heart. Crocodilians have a 4-chambered heart. Eggs are fertilized internally (inside the body). Some reptile species lay eggs from which the offspring hatch (oviparous) and others give birth to live young (viviparous). The life span of many reptiles can exceed 10–20 years, requiring a long duration of captive care.

Reptiles are ectotherms (cold-blooded) i.e. they maintain their body temperature by absorbing heat from the environment, so their body temperature changes with environmental temperature i.e. Thermoregulation. In contrast, most mammals and birds are endotherms (warm-blooded): they are able to maintain a constant body temperature despite changes in the environmental temperature.

Reptiles require a range of ambient temperature to be able to thermoregulate, which is essential for optimal physiological functioning, such as, movement, feeding, digestion, reproduction and immunocompetence.

Ectothermy has some advantages in that reptiles do not need major food sources to meet energy demands. For example, a reptile of equivalent size as a mouse will have just one‐tenth the energy requirement. This lower energy requirement and efficient food conversion has enabled reptiles to endure long hibernation and night cooling and to survive in arid deserts.

The main disadvantage of ectothermy is that all activity is limited by ambient temperature, such that many reptiles become inactive and vulnerable at night and have to hibernate when temperatures drop. They have a much lower aerobic capacity than endotherms and need to switch rapidly to anaerobic metabolism for any vigorous activity such as diving, chasing prey or escaping predation. Although anaerobic metabolism is independent of temperature, it drains energy reserves ten-fold. As reptiles also rapidly build up lactic acid, they easily get fatigued so cannot sustain intense activity levels for more than two to three minutes.

The preferred optimum temperature range (POTR) for reptile ranges from 20°C to 38°C but can vary by 4–10°C, depending on the species.

Mechanism of thermoregulation

Reptiles derive their heat by two mechanism viz. heliothermy or thigmothermy or a combination of the two. Heliothermy is the process of obtaining radiant heat by basking in the sun and is used by chelonian and diurnal lizards. Thigmothermy is acquiring thermal heat via conduction with hot surfaces and is common in nocturnal species.

Reptiles also use behavioral and physiological means of thermoregulation. They raise their body temperature by increasing their heart rate to pump warm blood from the core to the periphery. Their three-chambered heart can also shunt blood from right to left, to the peripheral blood vessels bypassing the evaporative cooling of the lungs. Lizards also heat up by increasing melanin pigment in their skin or by selecting a dark background. Snakes coil up to conserve heat and uncoil to lose heat, while lizards angle their body axis perpendicular to the sun to heat up and face the sun to cool down. Many lizards cool down by panting or gular fluttering, which is when they hold their mouth open to vibrate their throat. They also cool down by shade seeking and plunging into water.

Reptiles during winters

During winter months, low external temperatures cause lowered metabolism and activity rates. Reptiles in the wild have developed several different adaptation strategies for lower temperature, and seek suitable hibernacula such as burrows, dens, tree hollows, leaf litter, etc. for insulation, brumation and regulation of physiological processes. They also gravitate to an area having the temperature they need.

The captive reptiles do not have access to these kinds of choices they would have in the wild, hence they should be artificially managed.

Recommendations for the care of captive reptiles during the winters:

Housing

Reptiles require preferred optimum temperature range (POTR) to thermo-regulate. It is difficult to provide these temperatures to reptiles housed outdoors difficult during winter months. Hence, closed dens or shelters, where temperatures can be regulated using artificial heat, are recommended. These conditions can dry up the surrounding air hence humidity must be maintained by using moss, damp substrate/hides and frequent misting in order to prevent dehydration. Water bodies can be artificially heated and maintained at 29-30°C for large crocodiles, alligators and lizards.

Regulation of Photoperiod

Photoperiod is the amount of light received in a day. It is important for the welfare of reptiles and should be suitably altered during winter months. In general, day length and temperatures should be decreased during the winter. This reduces the chance of reproductive failure and disease in most reptiles. Exposure to 13 hours of light during the summer and 11 hours of light during the winter is recommended for tropical reptiles. In such cases, the artificial photoperiod can be altered to mimic that which is naturally occurring outside. Electric timers are economical and widely available. They can be adjusted and set to particular times or to mimic the natural photoperiod. The light source should be independent of the primary heat source.

Feeding management

There is a decrease in the metabolism due to low ambient temperatures during winters leading to poor appetite. Hence reptiles should be fed relatively less to prevent dietary complications and obesity. Less appetite also does not mean that they will not eat at all. Food must always be provided. Variety and method of presentation matching natural feeding cycles is a crucial aspect to consider for promoting some feeding activity.

Do’s and Don’ts

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