Sunday, April 17, 2016

Hibernacula




The condo complex where we live has a small pond on the grounds. Aerated by a fountain, the pond is full of life and sound from April to October. Ducks raise their young in the pond; frogs are heard "croaking" away in the early morning and late afternoon; and insects mark the surface with rings as they walk across on surface tension or swim from bottom to top. This pond is a controlled environment such that every fall it is drained and every spring it is filled. Most creatures leave the area for the winter; some must find ways to survive in the frozen mud or leaf and grass litter of the pond.

The frogs are an interesting case in point. There are many types of frogs in the world and I will not claim to know what type of frogs are living in the pond in Hawkwood, Calgary, Alberta. In fact, these frogs are so elusive that they are mostly heard and not seen. If you will allow me to speak in generalities, there are some interesting things we can learn about the hibernation techniques of frogs. NASA and other space agencies have a keen interest in studying the biology of frogs and asking questions about applications to humans and long space flights.[1]

Recent studies have shown that frogs use a number of techniques to survive winter temperatures. One method is to simply rest at the bottom of a deep pond or lake which does not freeze to the bottom. There, at a constant temperature of 4 degrees Celsius, the frog absorbs oxygen through its skin and slows its metabolic rate and heartbeat to a fraction of normal. Of course, this technique will not work if the pond is dry throughout winter. Some frogs migrate from one place to another to find a suitable wintering pond.

For the rest of the, shall we say, less fortunate frogs who cannot use the above methods, there is a more extreme procedure. These frogs must make a hibernaculum (plural hibernacula): a place to hide and hibernate for the winter and prepare to freeze their internal organs. These frogs dig down in the litter of the dry pond or burrow tunnels into the mud. Those in burrows create a space with the mud and secretions from their bodies to make a homely little tunnel that will meet their needs. Next, their circulatory system pulls many of the ribose sugars from their tissues and creates an antifreeze that is circulated in the outer extremities of the body. This antifreeze protects those extremities from freezing and signals the heart and other internal organs to slow down and prepare to be frozen solid. Yes, frozen solid! The heart, kidneys, liver and other internal processes will slow and freeze to the point that the heart rate may be as low as one beat per two weeks (beating only as temperatures rise enough to allow some movement of the heart muscle).[2] 

Then, as the sun begins to warm the mud, the grass, and the debris, a miracle of nature occurs. Those frozen organs and antifreeze filled extremities come back to life. Blood flows at normal rates, hearts pump, kidneys function, and livers live! Spring, that time of birth and rebirth, is witness to a resurrection of frogs. No wonder they come out of the mud singing “ribbety ribbet.” Life, for frogs who have survived minus 20 degree temperatures, is wonderful indeed. Next it is time for the frogs to find a mate, fertilize or lay eggs, and enjoy the new life they have been given before the whole process repeats once again. (Cue the “Circle of Life” music – or maybe the “Frozen” music – “the cold never bothered me anyway.”) One cannot help but be amazed by these wonderful little frog lives. 

"O Lord, what a variety of things you have made! In wisdom you have made them all. The earth is full of your creatures." Psalm 104:24 (NLT)   
“Just ask the animals, and they will teach you. Ask the birds of the sky, and they will tell you. Speak to the earth, and it will instruct you. Let the fish in the sea speak to you." Job 12:7, 8 (NLT)

Works Cited:
Emmer, Rick. How do frogs survive winter? Why don't they freeze to death? 1997. http://www.scientificamerican.com/article/how-do-frogs-survive-wint/ (accessed 2016-04-17).
Telegraph. "The Telegraph." Hibernating frog could help astronauts conquer Mars. 04 18, 2016. http://www.telegraph.co.uk/news/science/10936941/Hibernating-frog-could-help-astronauts-conquer-Mars.html (accessed 04 17, 2016).




[1] (Telegraph 2016)
[2] (Emmer 1997)

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