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Important evolutionary step discovered: body heat without shivering

17.06.2019: Endothermy, the ability to regulate body temperature independent of ambient temperature, was an important step in the evolution of many mammals and birds. In addition to shivering, so-called brown adipose tissue plays a key role in heat production. However, only around 20% of endothermic birds and mammals actually possess this specialised organ. A group of researchers from Vetmeduni Vienna has now managed for the first time to demonstrate that a third mechanism deep within the muscle tissue is sufficient to help newborn mammals lacking brown adipose tissue to survive without shivering despite cold ambient temperatures. According to the researchers, this mechanism could have played an important role in the evolution of many vertebrate species.

Muscle nonshivering thermogenesis (NST) was recently suggested to play an important role in thermoregulation of species lacking brown adipose tissue (BAT). Muscle NST is a biomechanical mechanism which produces heat independent of muscle contractions based on the activity of an ATPase pump in the sarcoplasmic reticulum (SERCA1a) and is controlled by the protein sarcolipin.

Proof from newborn wild boar piglets

A research group from the Research Institute of Wildlife Ecology at Vetmeduni Vienna investigated whether muscle NST could indeed play an important role in thermoregulation in species lacking BAT. They asked whether this mechanism could be sufficient for the maintenance of a stable body temperature in newborn wild boar piglets despite the cold temperatures in early spring. The team found that heat production in the newborns increased during the first five days of life even as shivering intensity decreased, which indicates an increasing contribution of NST. Sampling skeletal muscle tissue for analyses of SERCA activity as well as gene expression of SERCA1a and sarcolipin, the researchers found an age-related increase in all three variables as well as in body temperature.

Increased muscle NST considerably improves thermoregulation

The study, which was recently published in the journal Scientific Reports, clearly shows that the improved thermogenesis during the development of wild boars is not due to shivering but explained by the observed increase in SERCA activity, i.e. muscle nonshivering thermogenesis. “Our results suggest that muscle NST may be the primary mechanism of heat production during cold stress in large mammals lacking BAT, strengthening the hypothesis that muscle NST has likely played an important role in the evolution of endothermy,” explains study director Julia Nowack, who has since moved to Liverpool John Moores University in England.

“Taken together, our data show for the first time that muscle-based NST via SERCA1a plays a role in the thermoregulation of wild type mammals lacking BAT. In the evolutionary process, muscle NST was likely important during the colder night hours,” Nowack adds.

Stable body temperature – one of the most important mechanisms that arose during evolution

The regulation of a high and stable body temperature independent of climatic conditions is one of the most important mechanisms that arose during the evolution of mammals and birds. After decades of intensive research, it is now well-understood how mammals possessing brown adipose tissue (BAT) are able to maintain an optimal body temperature even in cold environments by using nonshivering thermogenesis (NST). However, only around 20% of endothermic birds and mammals actually possess BAT. The exact mechanism used in the absence of NST and BAT had so far been unknown, however. Researchers from Vetmeduni Vienna have now solved this scientific puzzle.

The article “Muscle nonshivering thermogenesis in a feral mammal” by Julia Nowack, Sebastian G. Vetter, Gabrielle Stalder, Johanna Painer, Maria Kral, Steve Smith, Minh Hien Le, Perica Jurcevic, Claudia Bieber, Walter Arnold and Thomas Ruf was published in Scientific Reports.