Preadaptivity of Non-Contractive Thermogenesis in the Evolution of Warm-Bloodedness in Vertebrates

Abstract

Most of the heat that is released in the vertebrate body is produced in the muscles during contractive (during movement or trembling) and non-contractive (without muscle activity) thermogenesis. Contractive thermogenesis is characteristic for all vertebrates, but it is not able to constantly maintain a high body temperature in animals. The main idea discussed in this article, and based on a large number of publications in recent years: the main biochemical base of warm-bloodedness in vertebrates is part of the cycle of contraction–relaxation of striated skeletal muscles, in which the act of muscle contraction somehow falls out, and the energy that should have been used for it is dissipated in the form of heat. This non-contractive thermogenesis, which is able to support the regional and general endothermy in vertebrates, can be considered the real biochemical basis of warm-bloodedness. Thus, the presence of skeletal muscles in all vertebrates and the common biochemical foundations of the contraction–relaxation cycle represent a single preadaptive property of the manifestation of non-contractive thermogenesis in all vertebrates, starting with fish, which is the basis for the evolution of warm-bloodedness. Therefore, it is understandable and unsurprising modern data that the first terrestrial vertebrates were most likely animals with high levels of both metabolism and body temperature.