Esa Hohtola
Department of Biology, University of Oulu, Finland

Why study endothermy?

"Endothermy (the elevation of body temperature by metabolic heat production) represents one of the
most significant developments during vertebrate evolution." Hayes JP & Garland T Jr.: The evolution
of endothermy: testing the aerobic capacity model. - Evolution 49:839 (1995).

Endothermy is a novel phenomenon in the evolution of vertebrates (Ruben, 1995). In its strict form, it is limited to birds and mammals, whose adaptive radiation occurred after the mass extinction of dinosaurs. While all metabolic events produce heat as a byproduct, endothermic species are able to use such mechanisms in a controlled manner to maintain a thermal gradient towards the environment. Endothermy has thus a pivotal role in homeothermy.

The two known thermoregulatory mechanisms of endogenous heat production that birds and mammals use for endothermy are shivering thermogenesis in skeletal muscles and brown adipose tissues thermogenesis (also called non-shivering thermogenesis, NST). Shivering is used by both groups while brown fat-related NST is limited to mammals. In addition to thermoregulatory thermogenesis, the obligatory component of thermogenesis in non-thermoregulatory tissues is also significantly higher in endotherms than other vertebrates. This is the basis of endothermy in thermoneutral conditions (Hayes & Garland, 1995).