Feb 5, 2014

Surviving the Winter through Hibernation

Little brown bats, native to Virginia, spend winters hibernating
caves or similar shelter. Bats also go into embryonic diapause 
in winter, breeding in the fall but delaying fertilization until
the spring. Photo by U.S. Fish and Wildlife Service.
Not being a lover of the cold, I’m not enjoying this winter so far. One bitterly cold day recently, I figured I either had to go out and face the enemy, or hibernate on the couch for the rest of the winter. Not being of a species that’s physiologically adapted to going totally dormant, I dragged myself out from under my down throw, bundled up and went for a stroll through the snowy woods. Finding a nice resting spot from which I could view the other side of the hollow through the now-bare forest, I sat and contemplated how animals here in Virginia do cope this time of year.

Basically, animals have three strategies: fleeing to warmer climes (migration), evolving a physiology that tolerates cold, or hibernating. Since hibernation was most on my mind, I started my research there, but soon ran into terminology issues, which are underlain by lack of agreement within the scientific community about the biological processes surrounding this state.

“Hibernation,” “torpor” and “dormancy” are often used interchangeably. In a 2011 article for The Encyclopaedia Britannica Advocacy for Animals website, Kara Rogers, Britannica’s biomedical sciences editor, defined dormancy as “the slowing of an organism’s metabolism to facilitate energy conservation in times of environmental stress, which often are characterized by extremes in temperature and by the lack of food or water.”

Dormancy is marked by topor—a state in which animals appear sluggish or lethargic. Such torpor can be light or deep. Rogers writes that “true hibernators represent the extreme end of sustained torpor.”

“Hibernator” is the really tricky word here. “Hibernation” generally refers to an animal’s becoming dormant in winter, while summer dormancy—for example, due to drought—is generally referred to as “aestivation.” While an animal’s lowering its temperature was long thought to be the key determiner of hibernation, metabolism suppression is more of the focus in current research. Both processes are interrelated.

As BBC Nature put it:

“Attempts at defining or triggering hibernation have … proved elusive. For example, merely exposing animals that hibernate to cold does not always trigger hibernation. Instead it may trigger hypothermia, a life- threatening pathologic condition. In addition, the duration for which an animal must remain in torpor for it to be qualified as a hibernator remains debatable.” 

BBC Nature adds that “considering that some animals exist in this state for the greater part of the year, it could just as easily be considered the default metabolic state and upregulation of metabolism merely a response to the availability of energy.” 

In any case, the timing for going into dormancy differs among animals. Some become dormant in direct response to worsening external conditions (consequential dormancy); others enter the dormant state well before adverse conditions set in (predictive dormancy). In the latter, internal clocks or external cues, such as shortening of the days, can initiate the change. 

Since ectotherms (“cold-blooded” animals), such as reptiles and insects, can’t regulate their internal temperature, the term “brumation” was added to the dormancy lexicon in the 1960s to apply to their state (particularly to reptiles) when they hibernate. The need for such differentiation has always been controversial.

Depending on the species and climate, hibernation can be intermittent or last through the entire cold season. Birds may just go into a light torpor at night when temperatures drop, while some hibernating mammal species vary the depth and length of their torpor. For example, ground squirrels (which include chipmunks and groundhogs) generally stay in deep torpor for the entire winter, while raccoons and skunks go in and out of torpor depending on availability of food.

One mark of hibernation that seems to be agreed upon is that animals do not eat, drink, defecate or urinate while in hibernation. This is mainly because of the lack of food and the amount of energy and water needed to find and metabolize what food might be available.

Rather than going into torpor, some animal species deal with winter cold and food shortages by halting only specific biological processes, known as “diapause.” Caterpillars, for example, take a break in their development cycle, entering into a chrysalis state in the fall and emerging as adult butterflies or moths in the spring. Reproduction can similarly be paused through “embryonic diapause,” in which some animals, such as bats, breed before winter but store the sperm until late winter or early spring, when fertilization is initiated.

The one thing to keep in mind when encountering animals that are hibernating is that it’s hard to be sure how deep into torpor they are. Animals brought out of torpor in the winter could die from burning off needed resources, and humans could be at the wrong end of a fully armed animal that is not happy at being roused. The best strategy, as with all encounters with wildlife, is to leave the animal as it was.

“To sleep, perchance to dream”:
The remarkable hibernation of the arctic ground squirrel

Arctic ground squirrels, also known as “parkas” in Alaska,
not only survive extreme temperatures by keeping their blood
liquid below the temperature at which it should freeze but
also increase their metabolism periodically during hibernation
for reasons that are not clear. Photo by U.S. Fish and
Wildlife Service.
Within the ground-squirrel family is a champion of surviving extreme cold—the Arctic ground squirrel (Spermophilus parryii). Not able to dig down far enough in the frozen soil of the Arctic to escape freezing temperatures, it has evolved to maintain a blood temperature just below freezing.

According to Bernd Heinrich, in his book Winter World: The ingenuity of animal survival, how the squirrel does this without any apparent antifreeze in its blood (an adaptation of some species, such as our native wood frogs) is not well understood but indicates that “supercooling” is likely involved. Supercooling is when the state of a gas or liquid is maintained when its temperature is lowered beyond its normal freezing point. It’s an unstable process—a mere stirring of an Arctic ground squirrel can start a crystallization reaction that can turn the rodent into an ice sculpture. However, taking this evolutionary gamble has enabled the squirrel to expand farther north than its cousins.

Another remarkable thing about the Arctic ground squirrel, according to Heinrich, is that, while it does maintain torpor during the winter, it also increases its metabolism periodically, raising its temperature “all the way up to when it is active” (98.6 degrees F.). Why does the squirrel do this? As Heinrich points out, research has shown that sleeping, dreaming, and oxygen
ating the brain—all of which need more elevated metabolism—have been shown to be essential to human health. Is it the same for this squirrel? According to Heinrich, this also remains a mystery.

1 comment:

  1. Don’t think of anything else just contact Dr Abalaka and purchase some of his herbal medication and your depression will go away. This was my state of mind when my doctor told me that i will not be able to conceive due to the Fibroid that was rolling in my family life and when i decide to reach out to the priest, and the Priest told me what to do in other to get the medication. Eventually I receive all the Herbal medications that cure my Fibroid and give me the chance to become a proud mother: Dr Abalaka is a great spiritualist, He did it for me, you can contact Dr on (dr.abalaka@outlook.com). If you are suffering from the following gynecology disease::
    High Blood Pressure (herbs to reduce your BP within 7days)
    Infection, regular body pains
    Blockage from the fallopian Tube
    Cyst from the ovaries
    Unpleasant smell from the virginal
    Irregular menstruation
    Weakness of the penis (not able to have sex with your partner or inability to satisfy your partner sexually)
    Watering sperm (low sperm count) not able to get woman pregnant.
    Infertility for easy Conception.......
    Erectile dysfunction treatment
    Skin diseases, Toilet infection and bad body odor…….Etc..
    Get your ex back
    Happiness in relationship
    Command respect in the society
    Enlarge your Penis/breast with no side effect
    Impotent solution
    Obesity solution
    Romanticism solutions
    Cancer of the blood
    Parkinson disease
    General consultation
    Those are the things he does, You can simply contact the spiritualist Dr Abalaka on (dr.abalaka@outlook.com) to get his Herbal Medication to cure your disease and put yourself on a motherhood side of life..