In Chapter 2 of Survival of the Sickest, Dr. Moalem discusses how
diabetes may have evolved to protect people from the cold. He also
describes how several animals, including the wood frog, have adapted to
survive the winter.
Thursday, March 21, 2013
Cold weather adaptions
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There are many different animals that apt to hibernate during the winter. One such species of animals that hibernate is the American Black Bear or ursus americanus. These bears can go on slumbering because their warm pelts and lower surface-to-mass ratio allow them to better retain body heat. This, in turn, enables them to cut their metabolic rate in half. Once hibernating, a black bear can doze for many months with a body temperature of 88°F or higher, which is within 12°F of summer levels.
ReplyDeleteDeer portray a different type of adaptation when it comes to dealing with cold environments. First, their winter coat has hollow guard hairs – like polar bears – and a fine hair beneath the guard hairs to provide outstanding insulation from the cold. Further, deer literally fatten up for winter. Fall grazing for the deer is full of high energy plants, seeds, and nuts that allow the deer to pack on fat stores for winter. Their metabolism in winter falls to one-half of what it is in summer, so the fat stores last longer in winter. Deer seek thermal cover and different food in winter. During warm months, deer range over larger areas, grazing on primarily grasses. Come wintertime, deer confine their movements within much smaller areas to conserve energy, and browse on woody plant material that is available above the snow.
These different adaptations are a product of evolutionary pressures and portray the diversity that comes out of different species’ ways of coping with these pressures. While some animals thousands of years ago were able to cope the cold through the natural regulation of their own body temperature such as is the case with the Black Bear, other ancestral animals such as the deer didn’t have the means to remain dormant for an extended period of time. Rather, they were able to adapt to a more confined diet which allowed their metabolism to compromise with the weather. This is why there are such adaptations as the bear and deer have differing benefits that come with their respective means of surviving. As bears are bigger and tend to require more meat in order to survive, it’s easier for them to sleep throughout the winter as finding fresh meat is more difficult in colder climates as opposed to deer who are herbivores. Since bears also have thick enough fur, this also gives the bears a physical adaptation which therefore allowed their ancestors to survive and reproduce into the species they are today.
In sharp contrast to both bear and deer, the wood frogs Dr. Moalem discusses about in chapter 2 actually, “give in to the cold entirely [as] it buries itself under an inch or two of twigs and leaves and then pulls a trick [in which] it freezes solid” (Moalem 41). Dr. Moalem also raised the possibility that humans with diabetes were actually descendants of people who were able to sustain cold weather by raising their blood-sugar levels which actually prove as beneficial in regards to lower temperatures. As blood-sugar concentration is high, this eliminates water within the human body as is the case with the frozen grapes and tree frogs mentioned in chapter 2 (Moalem 44), and such is how diabetes could have once been beneficial instead of just a chronic disorder it is today.
In my opinion, I think the most effective adaptation to cold weather is the deer’s in which an animal changes its living habits in accommodation to environmental conditions. Although diabetes could have proven beneficial to our ancestors living in extremely cold conditions, such isn’t the case with the disease today, and most people have other means of enduring cold weather nowadays. This connects again with the deer in which they change their eating and living habits during the winter to make do with what they have, but they can still roam around and remain active instead of staying dormant like the bear and wood frog. This is why I feel like its adaptation is the most effective method of cold weather survival because it gets the most out of its time and life as well as it remains active even during the cold conditions, which also allows it to be more flexible to unique weather conditions (i.e. some years may have obscure weather which can throw hibernating animals off).
ReplyDelete(Lois Kim, lokim3@students.d125.org)
The evolutionary pressures for animals living in colder climates have led them to hibernate. Hibernation is an important part of many animals’ lives. During this time period, Cosmos Magazine reports, that by slowing down their metabolism, animals can output far less energy. This is because during the winter, food supply is short, and once temperatures rise again they can easily find more food.
ReplyDeleteOne interesting animal that hibernates in the winter is the arctic ground squirrel, also known as Spermophilus parryii. This squirrel is able to hibernate from earl September to late April. It cools its body to -2.9°C, this is the lowest known naturally occurring temperature in mammals. But, even while it cools its body to -2.9°C, it keeps its brain, and other important parts of the body involved in regulating and maintaining energy metabolism above zero. Molecular biologist, Matthew Andrews, explains that this would never be possible in humans “the chemical reactions in our bodies just can’t take place”. This arctic ground squirrel is very well adapted, during hibernation, every week, the squirrel shivers without waking, re-warms to 37°C for about 12-20 hours and goes back to hibernation without any tissue damage. The reason it is able to do this, Andrews explains, is due to PDK4 and PTL enzymes that switch over metabolism and help cardiac physiology to work at squirrels’ heart. It is found in the squirrels’ heart and “it can burn fat in the cold and allow heart to continue beating”. (http://www.cosmosmagazine.com/features/total-shutdown/)
An animal that “toughs it out” during the winter is the mink. The mink grows thick layers of insulating fat and have specialized fur. They also have a high metabolism and thick fur to help keep them warm. But, they store little fat, so they have to keep hunting and eating all winter. They are good hunters both on land and in water and eat anything. (http://www.friendsofeloisebutler.org/ pages/gentian/57_1/wintersurvival.html) They do not nearly have a complex adaptation to winter as the arctic ground squirrel or wood frogs. The adaptation of more coats of fur relates to Big Idea #1. The cold weather drives the diversity and unity of life. Most squirrels in suburban and urban areas such as the common gray squirrel seen around here don’t hibernate. Their body temperatures remain fairly constant throughout the year. But, the arctic ground squirrel, which lives in the Arctic Circle up north, like Alaska, has a complete different adaptation to the winter. It has a complex system of hibernating where it is able to control the temperature of its body while keeping vital organs functioning. This shows the diversity within a species. Because the winters up north are much colder and harsher, it was a trait that was selected for up there but unnecessary down here.
Both these animals have very different adaptation styles compared to humans and the wood frog. The wood frog freezes itself, the arctic ground squirrel uses a special enzyme to burn fat during the cold and keep vital organs functioning, humans shiver and stop the blood flow to unimportant part of the body (first toes and finger, then to other body parts) to keep the important organs in our body still working, the mink grows more layers of fur and has a naturally high level of metabolism. I think the animal in this group that has the most effective method of cold weather survival is definitely the arctic ground squirrel. It is using a special enzyme that specifically works better in the cold. This enzyme is a key part of its survival. But, in my opinion it is the most effective method because it is something that has never been seen before by any other mammal. It is able to cool its body to a low of to -2.9°C, a body temperature no other mammal can survive with. Even though it isn’t active, it is using it’s fat it was storing all summer and fall as energy. The fact that this squirrel is able to change its temperature while it is still asleep is amazing.
I disagree with Lois, though it may seem that being active during the winter may seem beneficial, I believe it is more dangerous to the animal. It doesn’t have a secure place to stay and has more of a chance to die. If it can’t find enough food that winter due to the harsh winter, it will die before a hibernating animal. The hibernating animal has a higher chance of survival because it prepares itself for those harsh winters by eating more during the summer and fall and keeps that extra fat incase.
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