Mesothermy

Mesothermy refers to a range of body temperatures that fall between the typical endothermy of warm-blooded animals and ectothermy of cold-blooded animals. Organisms exhibiting mesothermy, sometimes called "intermediate-temperature" or "moderate-temperature" regulators, can generate some internal heat but not enough to maintain a consistently high body temperature independent of the environment. Their body temperature often fluctuates within a range, influenced by both metabolic heat production and ambient conditions. This strategy can offer advantages such as reduced energy expenditure compared to strict endothermy, while providing better thermal stability than pure ectothermy, especially during moderate environmental conditions or periods of moderate activity.

Examples of mesothermy can be observed in various animal groups. Some fish, like tuna and certain sharks, can retain metabolic heat in their swimming muscles, allowing for higher temperatures than the surrounding water. This regional endothermy improves muscle performance. Some insects, particularly during flight, can elevate their body temperature through muscle activity, allowing them to fly in cooler conditions. In reptiles, while generally ectothermic, some species show limited capacity for internal heat generation that can lead to intermediate body temperatures under specific circumstances. The degree of mesothermy can vary significantly, and it is sometimes viewed as a transitional or facultative state rather than a distinct physiological category. It represents a flexible approach to thermoregulation, balancing energy costs with the benefits of a buffered body temperature.