Rapid metabolism change helped mammals to thrive in colder climate

Hedgehogs, rabbits, primates and even giraffes have all benefited in the evolutionary race because of their ability to adapt their metabolism to cope with climate change, according to new research.

A new study, published in Nature, reveals that mammalian ancestors benefited in the evolutionary race through their ability to adapt their metabolism beyond the constraints imposed by body temperature. They were able to colonize colder environments or higher latitudes, allowing them to thrive when the Earth's climate cooled.

It was previously believed that the animals' basal metabolic rate (the rate at which energy is used to maintain the body) was closely related to the animal's body temperature. However, this research shows that mammals have successfully decoupled this relationship to allow their metabolism to evolve rapidly and adapt over 165 million years.

Jorge Avaria-Llautureo, evolution biologist at the University of Reading and lead author of the study, said: "The research focuses on understanding the origin of mammals' metabolic diversity in response to the rate at which they lose heat in the environment.

"Colder environments increase the rate of mammalian heat loss and, to maintain a constant body temperature, this loss is then compensated by an increase in metabolic rates as long as resources are available to fuel the metabolic elevation.

Previous research has worked on the principle that body temperature and metabolism are closely linked because metabolism is the main source of heat and body temperature itself affects metabolic rates.

However, the new study found that natural selection was able to quickly adapt animal metabolism regardless of body temperature, which was true for more than 90% of ancestral mammals, including bats, carnivores, hedgehogs, marsupials, primates, rabbits, rodents and even toad ungulates.

Chris Venditti, evolution biologist at the University of Reading and co-author of the article, said: "The article challenged the hypothesis of ecological and evolutionary theories that basal metabolism evolves in tandem with body temperature. These physiological traits have evolved under distinct selection pressures, leading to different pathways to their modern diversity. It also helps us to understand the evolutionary benefits that have led to the diversity of mammalian energy expenditure."

The article also examined the evolutionary trajectory of metabolism in birds. They found that basal metabolic rates and body temperature were also dissociated at least 36% of the time, but that avian metabolism was not affected by changes in ambient temperature.

Dr. Avaria-Llautureo said, "The difference we have observed in birds is probably due to the fact that feathers provide better heat retention than fur. Their feathers have helped them to isolate their internal environment and maintain their physiology more constant than that of mammals in an ever colder historical environment."

Mammals that have particularly benefited from the evolutionary advantage include:

hedgehogs (order Eulipotyphla)
even-toed ungulates (Artiodactyla control)
carnivore (order Carnivora)
primates (order of Primates)
rabbits (order Lagomorpha)
rodents (Rodentia control)