Question

Consider a lizard and a bird, each of 20g body mass and each with optimal body temperature of 40°C. Discuss in detail the thermoregulatory strategies (physiologic and behavioural) they employ to survive the SoCal winter (minimum night temp 2°C, maximum day temp 10°C) and summer (minimum night temp 25°C, peak day temp 50°C). Remember that these ambient temperatures are reported for shade! For each species, draw a graph how the body temperature and metabolic rate change over the course of 24 hours in each season.

What if a six footer Komodo dragons got loose and went on the lam on a school campus? How would its thermoregulation differ from that of the 20g lizard? (assume same optimal temperature)

Answer 1

Based on temperature regulation, animals can be divided into basically two groups that are endotherms and ectotherms. Endotherms use metabolic heat i.e., energy/heat generated in the body by various metabolic processes, to maintain a stable internal temperature. This temperature is different from the one of the surrounding environment. Mammals and birds are typical examples of this type.

Endotherms, on the other hand, take the temperature of the environment i.e., they do not use the heat generated by metabolic processes to maintain body temperature. Their body temperature is the same as that of the external environment. Lizards and snakes form a typical example of this group.

Natural selection helps these organisms maintain appropriate body temperature by various adaptations. These can be behavioral, anatomic, and physiological and help survive extreme weather conditions by regulating the exchange of heat with the surrounding environment.

Behavioral and physiological adaptations

Lizards often bask on a hot rock to increase their body temperature and warm-up. During extreme heat, they can go to shade and burrows or hide under a rock. The shuttle between shade and sun i.e, cold and hot microenvironments helps in modifying the heat flux by altering the surface area exposed to the heat source or sink and by regulating the activity times. Lizards undergo hibernation during extreme winters and significantly reduce their activity. Lizards warm themselves using insolation (absorbing heat from the sun) and conduction(absorbing heat from the ground). Lizards can change color. Converting to a darker color helps them absorb more heat.

Birds seek shade during extreme heat. For surviving extreme winters, birds fluff out their feathers which creates air pockets for insulation. Birds can stand on one leg or cover both legs with their feathers by crouching to protect bare skin of leg from extreme cold. They can also tuck their bills in feathers to breathe warm body air and also protect the beaks. During day time they take advantage of solar heat by exposing increased surface area (by spreading their feathers and tail) to allow heat to warm their body. Shivering also helps birds increase body temperature. Small birds may gather together in a small space and lie tightly together to maintain warmth. Some birds reduce their metabolism at night to conserve energy.

Bird's feathers provide excellent insulation against cold and some birds grow extra feathers. Oil covering the feathers also adds to the insulation and waterproofing. Legs and feet are covered with scales to prevent heat loss. Birds can reduce blood flow to extremities to reduce heat loss. Some birds have fat reserves for extra insulation and energy source.

Lizards and Komodo dragons

Lizards engage in sun shuttling behavior more commonly than larger sized Komodo dragons. Komodo dragons are more sedentary and rely more on microhabitat selection. They employ mouth gaping evaporative cooling to prevent overheating and maintain optimal temperature.

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