Using a cooler for hibernation

[edward]

Hi Alan,

You beat me to it, I was digging out my copy of the Concise Oxford Dictionary of Zoology.

There is some argument as to whether some of the aquatic turtles actually are hibernating as they move up and down the thermocline as needed to maintain optimal body temperatures and species such as Glyptemys insculpta and Chelydra serpentina are rountinely seen actively swimming under the ice. In some species, the exposure to the cold appears to not be needed to reset the clock as a change in photoperiod and a temperature drop seem to work as well but this is very species dependent(a temperature drop and change in photoperiod are all that is needed for Clemmy guttata and Pseudobranchus a. axantha for examples in my experience (also a bunch of colubrids work this way)).
The reason I used (and prefer) the word torpor even though it is probably better applied to endotherms is this is how a lot of reptiles and amphibians do function. They are inactive but as long as they are not totally frozen solid can and do routinely move as needed and can become much more active with a few degree increase in during the day. As far as I can tell in the literature, herps that do not freeze as part of thier overwintering strategy do not sleep but are still aware but inactive (many denning snakes behave this way).

Ed

 

[mark]

Yeah thanks Alan. I was wrong, the definition of hibernation would appear to rely on the physiological changes rather than the inactivity. So by the encyclopedia interpretation, if a caudate is inactive and it's physiology changes i.e. heart rate, breathing or metabolism slows, it is by definition, hibernating rather than in torpor.

 

[colin]

well, that just confused the point... I think its a case of, rightly or wrongly, that the actual definition of the word has been muddied over time and its definition seems more... flexible?

As far as Swallows hibernating goes. The old thoughts up here on swallows was that they hibernated on the bottom of the pond. The reason being that the reed beds were the last place people seen them before the winter and then they appeared the next year, they asumed they went into the water rather than Africa.... makes sense.

 

[edward]

Hmm,
Except that the newt is not physiologically controlling its body temperature and any physiological changes are the result of the cold slowing the metabolism down (with the exception of those amphibians that freeze solid) and not to any internal physiological function...

As a side note to this, the idea that they hibernate is where the idea came from that euthanizing amphibians in the freezer is an acceptable practice. This has been shown to not be the case as the animals are still awake and functioning and can feel and unless so cold they are immobile react to the stimuli (in this case pain) but even when so cold as to be immobile they can still detect the stimuli.


Ed

 

[mark]

Ed, that would imply that cold blooded animals are not capable of hibernation. I think the survival strategies for both warm blooded and cold blooded animals are too similar to say that one is true hibernation and the other not. Endotherms have much higher metabolism to control which requires some internal intervention but the strategy and end results are the same for both.

 

[william]

sorry to confuse this further, but surely we should use the term brumination, i quote from Alan's post:

"Some reptile species are said to bruminate or undergo brumination, but this is merely another term for hibernation, usually in the context of an induced hibernation in captivity necessary to reset the animal's biological clock for a new breeding season."

surely for the hobby we use brumination...

 

[ester]

Check this out..
http://en.wikipedia.org/wiki/Hibernation

Newts are mentioned

 

[edward]

Hi Mark,
That is why I do not like the term hibernation for a wide variety of herps that undergo a period of cold induced hypoactivity (which I refer to a torpor (which I think fits under the last sentence in Alan's post above)). The survival strategies may be the same but the mechanisms to ensure that survivial occurs are not the same even though they may be commenly referred to as hibernation. I am not saying that there are absolutely no amphibians or reptiles that use hibernation as a survivial strategy but the vast majority do not as they simply have a thermally dependent reduced activity level.

Amphibians undergo a external thermally induced period of inactivity, not a internally regulated period of reduced metabolism that includes sleep (as is seen in mammals). (although, there are physiological changes in response to anoxia due to a reduced ability to respire and/or if the animal is underwater due to this inactivity).If the temperature is sufficiently high enough to permit movement the amphibian (or reptile) can attempt to behaviorally manipulate its temperature though movement from one location to another but if the temperature is too cold to permit movement, the herp can/will die from hypothermia (species, acclimation and Tmin dependent).
Some of the recent literature no longer uses the term (at least in the abstracts I can access) hibernation/brumination with respect to herps. (A good example is Hypometabolic homeostasis in overwintering aquatic amphibians http://jeb.biologists.org/cgi/content/abstract/200/2/387)

Some comments

Ed

 

[mark]

Thanks Ed. To a non-biologist, like myself, parts of those abstracts are beyond my understanding but still it is an interesting topic of discussion/reading and you must forgive me if I misinterpret in some way.

You say that the metabolism of overwintering amphibians is not internally regulated and yet the abstract about metabolic rate reduction in Rana temporaria concludes that “The results indicate the metabolic conditions required for the submerged animal to enter a hypometabolic state and show that the frog adopts an integrative physiological response whereby the intracellular milieu is preserved at the same time as metabolic rates are being significantly depressed.” Which to me suggests that in the right conditions R.temporaria, at least, has the ability to regulate it’s metabolism beyond those that the environmental conditions impose. Does this mean that some ranid frogs are “true” hibernators? If so do newts that overwinter in ponds also posses hypometabolic skills?

 

[edward]

As I understand it, this does not initially occur until the frog enters into a oxygen debt and the metabolic depression is due to the oxygen debt (the time for this to occur would be variable and based on tissues in question, temperature and activity level). Skin tissues can readily unload CO2 into the water (especially if there is any sort of current flow to remove the CO2 from the skin) but deeper tissues will not have this ability and as the core temperature decreases the rate of blood flow decreases forcing anaerobic conditions on the tissues and the resulting reduction in metabolism. Even though there is a reduction in metabolism, the reason is not to conserve energy (as in mammalian hibernators) but to avoid the consequences of increasing oxygen debt. This same mechanism is used in at least one tropical anuran under short term periods of torpor as Bufo marinus has a similar metabolic response even while undergoing apnea for about an hour.
(See http://www.scielo.br/scielo.php?pid=S1519-69842003000100006&script=sci_arttext&tlng=en )

Ed