On pages 40-48, Dr.Moalem discusses the adaptations expressed in Rana Sylvatica or wood frog. This species of frog displays the unique characteristic of being able to completely freeze during the winter months and then "restart" once their tissue thaws out. This relates to Big Idea #1 concerning how evolution drives diversity and unity of life. The environment in which the wood frog can be found (from Northern Georgia all the way to Alaska and north of the Arctic Circle) selected the traits in this species which aided in survival and reproduction. How are the traits exhibited by the wood frog related to evolution and the survival of the species today?
Many of the bodily processes exhibited by the wood frog during this period of freezing are similar to the processes done by a person who has been diagnosed with type I diabetes.
While the idea that diabetes was a trait selected for in an environment of low temperatures and low food supply is still considered a theory, would you support or reject this belief? Provide details and examples either mentioned in the book or found on your own to support your argument. Try to relate your conclusions to Big Idea #1 concerning evolution and more specifically, how the environment determines which traits are favorable.
(Tim Mielczarek tmielcz5@gmail.com)
Update (3/13/2013)
http://www.pbs.org/wgbh/nova/nature/frozen-frogs.html
The wood frogs’ ability to freeze during the winter and then thaw in the spring is a selective advantage, as it allows them to survive during the winter. Once the frog’s skin senses freezing temperatures, it quickly moves water out of the blood and into its abdomen (Moalem 43). The frog’s liver then pumps large amounts of glucose into the bloodstream, significantly lowering the freezing point of the frog’s blood (Moalem 43). The frogs use this mechanism in order to combat the effects of freezing temperatures. Unlike other hibernating animals, frogs do not have the fat deposits to insulate their body from freezing temperatures. The process of increasing blood sugar prevents ice crystals from forming inside the frog’s bloodstream, and potentially damaging the frog’s cells.
ReplyDeleteDr. Moalem then relates the frog’s mechanism for withstanding cold winters to diabetes in humans. Humans most likely to have a genetic propensity for diabetes descended from “places most ravaged by the sudden onset of an ice age about 13,000 years ago” (Moalem 44). Furthermore, “in areas of cold weather, more diabetics are diagnosed in cold months” (Moalem 45). Thus, it can be hypothesized that the spike in blood sugar seen in diabetics could be partially attributed to an evolutionary response to cold. A spike in blood sugar would allow earlier humans to stay out in the cold longer while hunting for food, thus giving them a selective advantage over those whose bloodstreams have a higher freezing point.
I would agree with the idea that diabetes was a trait selected for in an environment of low temperatures and low food supply. A Science Daily article found that “vitamin D may be protective against type 1 diabetes” (2013). Humans typically receive less vitamin D in the winter, as there is less sunlight. Therefore, it can be hypothesized that these low vitamin D levels during winter can cause the human body to increase blood sugar concentration as an evolutionary response. The increased blood sugar during times of low temperature and vitamin D intake in humans and wood frogs relates to Big Idea #1, which concerns the process of evolution. The spike in blood sugar levels during winter months in both humans and tree frogs is likely an evolutionary response for both species. The increased blood sugar would allow earlier humans in cold environments with low food availability to hunt longer, giving them a selective advantage over those whose blood would freeze faster. In wood frogs, the spike in blood sugar allows them to hibernate during winter without freezing their blood and damaging their own cells.
On page 64, Moalem describes wood frogs with a trait of freezing itself and restarting for the wood frogs relate to the big idea 1. The big idea 1 states that "life continues to evolve within a changing environment." The wood frogs probably evolved into having this trait, because the ancestor of wood frogs were having hard time surviving in winter, but there were some ancestor specie with genetic variations that enabled the ancestor specie to freeze and survive and reproduce. Eventually, there probably was a directional mode of selection for the ancestor specie with the ability to freeze and survive and reproduce. Finally, the ancestor organisms who had the trait probably grew in number and evolved in the wood frog today.
ReplyDeleteThe way wood frogs freeze is very similar to people with type 1 diabetes. The wood frogs' liver releases large amount of glucose into the bloodstream prior to freezing. In the same way, people with type 1 diabetes have more glucose in their bloodstream than normal.
I do believe that diabetes was a trait selected for low temperatures and scarce food. Many organisms including bull frogs and some plants, resist freezing up their inside organs and cells by releasing sugar. Sugar helps to resist freezing. Thus, people with diabetes where their sugar level is too high would have been favored to survive from freezing up. Also since people with diabetes have a high glucose level in their bloodstream, diabetes patients don't need to take in as much food as people without diabetes. Thus, people with diabetes would have been favored in an environment with cold temperature and scarce food.
http://www.sciencedaily.com/releases/2010/08/100817171603.htm
http://frogmatters.wordpress.com/tag/wood-frog/
http://www.sciencedaily.com/releases/2012/09/120910142632.htm
woosik choi (wchoi3@students.d125.org)
The wood frog, Rana Sylvatica, displays traits related to the survival and reproduction of the wood frog today because of the environment it lives in. It has adapted to its individual environment. One thing it shows a trait of is cryptic coloration (Campbell 1201). The wood frog blends in with its background making it difficult to see for predators that hunt in the winter when the frog is frozen. The wood frog also the only frog that has developed the survival strategy to withstand the freezing of its cellular body fluids during winter hibernation. (http://intl-jme.endocrinology-journals.org/content/21/2/153.full.pdf) This helps because the frog will freeze and die when the weather gets cold, so by figuring a way to freeze without dying is a survival mechanism.
ReplyDeleteI would support the idea that diabetes was a trait selected for in an environment of low temperatures. In chapter 2, Dr. Moalem discusses why this might be a credible theory. The rapid climate change and ice ages made people with Type 1 Diabetes more likely to survive and reproduce because of their disease. This relates to Big Idea 1: The process of evolution drives the diversity and unity of life. The cold caused the development of Type 1 Diabetes, which during the time of the ice age was a selective advantage, because it lowered the freezing temperature of the body, so people could withstand a lower temperature without dying.