Natures wonders: not all mammals warm-blooded (Introduction)

by David Turell , Monday, June 13, 2016, 22:55 (3083 days ago) @ David Turell

There are many mammals that have their temperature drop to very low numbers, although most mammals have a rather steady body temperature in a small range:-http://www.bbc.com/earth/story/20160609-time-to-bust-a-myth-not-all-mammals-are-warm-blooded-"Mammals are animals that are (mostly) covered in hair and that nurse their young with milk. They include duck-billed platypuses, mice, elephants and human beings.-"It is true that all mammals can produce heat from within, a talent known as endothermy. This means that most mammalian species do indeed have warm blood. They maintain a high and fairly constant body temperature, which allows them to function efficiently across a range of conditions.-"This is why entry-level textbooks often refer to mammals as being "warm-blooded". This distinguishes them from "cold-blooded", ectothermic creatures whose body temperature is wholly dependent on their surroundings.-***-"In a classic paper that made the front cover of Science in 1989, physiologist Brian Barnes of the University of Alaska Fairbanks studied the squirrels during hibernation. He found that they drop their core body temperature below zero, in one instance to -2.9C, without freezing solid.-***-"For instance, newborn mammals' body temperature is entirely dependent on the temperature of the environment. The ability to produce internal heat only kicks later in development.-***-"Smaller mammals - including many rodents, insectivores, bats, marsupials and even some primates - have evolved a way to push this temperature reduction much further. They enter an energy-saving state known as daily torpor.-"For instance, the common blossom-bat can lower its body temperature from around 36C at night to just 20C in the day. Similarly, the Brazilian gracile opossum seems able to chill at 16C for hours on end.-"In a more extreme case, Madagascar's pygmy mouse lemur will spend around 10 hours a day in torpor, its body temperature falling below 7C.-***-"'Naked mole rats are interesting from a thermoregulatory standpoint, because they don't control their body temperature very well," says Boyles.-"This does not mean they are failed mammals. Rather, it is simply that they spend all their lives in underground tunnels where the temperature is fairly predictable, usually somewhere between 29 and 32C.-"'They don't have to spend the energy on thermoregulation," says Boyles. "It's the perfect example of an evolutionary adaptation, not a physiological limitation."-***-"Michael Le Page of New Scientist points out that hyraxes also cannot control their internal body temperature. But unlike naked mole rats, they live out in the open and have to deal with changing temperatures. To survive, they must bask in the sun to warm up, as many reptiles do."-Comment: Mammals burn so much energy daily it is easy for them to maintain a steady body temperature. Humans in the AM are 97+ and usually don't above 98.6 F by late afternoon. But a temperature that is too high can burn the brain. Heat stoke can easily occur at temps of 106 F and higher. Over 108 can destroy the brain, if not cooled quickly. Mammals generally have tight controls and several heat loss mechanisms for this reason. By the way, the hyrax is the closest evolutionary relative to the elephant, and they are large rabbit size or slightly bigger weighing from 4.4 to eleven pounds.