Endothermia

Endothermia, or endothermia, is a physiological strategy in which an organism maintains a stable, relatively high core body temperature through internal heat production and regulation. In animals, endothermia is most closely associated with birds and mammals, which typically sustain body temperatures well above the surrounding environment. Some species outside these groups exhibit regional endothermy, in which heat production is localized to specific organs or limbs to enhance performance.

Endothermia relies on metabolic heat generated by cellular respiration and on regulatory mechanisms that minimize heat loss. Heat production occurs mainly through basal metabolic processes and, in many mammals, shivering or non-shivering thermogenesis. Insulation from fur, feathers, or fat reduces heat loss, and vascular adaptations such as countercurrent heat exchange limit heat loss in extremities. Evaporative cooling mechanisms, including sweating or panting, help prevent overheating when ambient temperatures rise.

Birds and mammals are the most widespread endothermic groups. Regional endothermy is observed in certain fishes, including some tuna, billfishes, and sharks, where heat is generated and retained in specific regions to enhance muscle performance in cold waters. The opah (Moonfish) is a notable example of a fully endothermic fish. In these groups, endothermy entails higher metabolic costs, shaping activity patterns and geographic ranges.

Evolutionary perspectives on endothermy suggest multiple origins and varying degrees of thermoregulation among lineages. The trait is energetically costly and influenced by habitat, food availability, and life history. Endothermy remains a focal topic in comparative physiology and evolutionary biology.