The seed of this mornings discussion in neurobiology was “Time, Love, Memory” by Jonathan Wiener. As has been the norm in past weeks we met in the on campus cafe bringing along with us four insightful questions each to keep the discussion rolling along throughout the hour. Wiener describes later in his book (p192) the three necessary components of living clocks. Living clocks are the basis of circadian rhythms and must have an input pathway so that the clock can be reset by the sunrise and sunset. A good example of why this is important is that humans actually have a twenty-five hour clock that resets itself everyday to correlate to the actual day length of twenty-four hours (23 hours, 56 minutes, and 4.1 seconds for any physicists reading this). People who are blind or people who are not exposed to the sun at all will exhibit a twenty-five hour clock, out of synchronization with the earth’s rotation.
So my question was about animals that live near the poles. How do polar bears or lynxes reset their clocks in the arctic summer when the sun doesn’t set? Some thoughts were that perhaps the living clocks are reset by magnetism but quickly realized that there is no shift of magnetism that corresponds to the length of a day. Another thought was that if it’s always light out, does it matter when the polar bear sleeps? The polar bear could have a period of activity, followed by a period of decreasing activity, and then rest and sleep. Lynxes often hunt at night and rest during the day but if it’s always light out does their clock remain synchronized with the earth’s rotation? PZ mentioned there isn’t much research pertaining to this but If anyone knows of any interesting papers that would enlighten this topic post them up.
References: Jonathan Wiener. “Time, Love, Memory.” Vintage Books, A Division of Random House, Inc. New York. 1999.
I think this is proof of Intelligent Design!!!! OK, just kidding, of course. But this is the sort of fascinating stuff that trips the trigger of design advocates. When you come up with a godless theory, let us know.
Not to go OT here or anything, but earth’s tides change on roughly a 25-hour “day” from lunar influences. Could a “circadian (hu)man” be looney?
This is how reindeer do it (and PZ wrote about that study a long time ago as well).
If I recall correctly, in The Other Side of Eden Hugh Brody describes the Inuit as staying up and sleeping in later and later as the days in the Arctic get longer, until by mid-summer they’re sleeping during the day and up all night. I don’t recall that he mentions why this is the case, but it is interesting to think that animals (such as humans) living in the high Arctic might vary their sleep cycles so dramatically in different seasons.
I concur with #2.
Studies have shown that when you deprive human experimental subjects of a sense of time (lock ’em in a room without a clock, etc.), they settle into a 25-hour cycle, which is also a “lunar day”. I think there have also been some studies that have shown that human women tend to menstruate on a 28-day cycle, but I’ve no first-hand experience with that.
So I theorize that our bodies are sensitive to lunar cycles, though our minds might not be, and when our minds have nothing to synchronize on, our bodies latch onto tides. Maybe it qualifies as ESP, but not as crackpot-ish.
Only way to test my theory is to remove humans from earth; guess I should apply for a research grant while Bush is anxious to get to the moon. Could be a good research subject for the space station occupants.
What about the humans posted to the south pole for extended periods?
at least for us humans, i know from experience, the arctic day (and night) can be quite difficult to cope with. not everybody can adjust, and many don’t adjust well. i’ve no clear idea whether other species do any better.
i suppose the angle of the sun might be one indicator during summer, or possibly the polarization patterns of the sky for species that can sense those. but the darkness in winter just plain bites.
#2 and #5: Unfortunately, as you get closer to the Earth’s rotational axis, the magnitude of the tides falls off, too. By the time you get to the pole, there should be hardly any tide at all.
tceisele wrote; “#2 and #5: Unfortunately, as you get closer to the Earth’s rotational axis, the magnitude of the tides falls off, too. By the time you get to the pole, there should be hardly any tide at all.”
Is that right? In my experience the magnitude of tides does vary with latitude but in the opposite direction you’ve indicated. Tides near the equator are very small while further north (and south) they get quite large, local topographical variabilty notwithstanding.
Of course, I’ve never been anywhere near either pole, but I have SCUBA dived from as far North as Vancouver, BC and Newfoundland to as far south as Hawaii and the windward islands of the Caribbean. Tides in those northern latitudes are often in excess of three or four meters while in the Caribbean and Hawaii they are measured in cms.
Do the tides then drop off (in terms of magnitude) as you head even further north than Vancouver and Newfoundland?
It’s pretty easy here in central Alaska to tell when it’s daytime and when it’s night in the summer, even when the sun’s still up at midnight. There’s still a very clear 24 hour cycle; it just doesn’t involve complete darkness.
From the abstract of a more recent paper by the group cited by Coturnix:
Melatonin secretion upon exposure to darkness did not conform to a circadian pattern and did not, therefore, support the hypothesis that pineal activity in reindeer is tightly regulated by circadian mechanisms. Instead the secretion of melatonin appeared to be acutely and directly sensitive to ambient lighting. The results are consistent with a model in which Arctic resident animals have adapted to extreme photic conditions by disconnecting the generation of the pineal melatonin signal from their circadian machinery and relying, instead, on its being driven by the LD cycle for just a few weeks annually in spring and autumn.
Reference: Stokkan et al. (2007) J. Pineal Research 43, 289-293
My colleague across the hall receives that journal (in fact I think he’s an editor), so if you want the article and can’t access it, let me know.
One minor nit–his name is “Weiner”.
Great blog!
When visiting my son and his family in the Yukon this past summer, I wondered what do strictly nocturnal (as opposed to crepuscular) mammals such as northern flying squirrels do under the midnight sun. What about bats?
I work in a lab that studies insect cold tolerance, and there’s a really good book that we look at a lot: Insect Clocks by D.S. Saunders.
He describes circadian rhythms in insects as being governed both by photoperiod and thermoperiod… I have no idea whether temperature would affect mammals that much, but according to Environment Canada there’s at least a 10 degree difference between night and day up North.
I liked the sound of the planet Arthur Dent ended up on with a 26 hour cycle. You could always have a sleep in, even if you had been up ‘late’.What would be needed to slow the rotational velocity down that much?
at least for us humans, i know from experience, the arctic day (and night) can be quite difficult to cope with. not everybody can adjust, and many don’t adjust well.
But the darkest time of the year is not necessarily psychologically the hardest.
…what do strictly nocturnal (as opposed to crepuscular) mammals such as northern flying squirrels do under the midnight sun. What about bats?
In most places there will be plenty of twilight for the bats. As Jason said, there’s still a light and a dark period.
…this reminds me of helping with the haymaking as a child and watching the bats snap up ghost moths in the dusk. That was cool.
The mean solar day is as near as makes no difference to 24h 00m 00s. In fact, the original definition of an hour was “one twenty-fourth of a mean solar day”. The current mean solar day is about two milliseconds longer than exactly 24 hours. A mean solar day is the average elapsed time between consecutive local noons, averaged over a long timebase.
The poster mentions a different period in a parenthesis: 23h 56m 4.1s. This is the length of a sidereal day, which is the average elapsed time between meridional transits of an arbitrarily-chosen distant star. Our biological clocks resynchronise, not to the stars, but to the sun, and so the length of the sidereal day is not relevant.
Thermoperiod would not work in mammals and birds. One can entrain individual SCN pacemaker cells in a dish using temperature cycles. But, whole animals require such vast differences between cold and warm that the entrainment is most likely due to cycles of stress or cycles of exercise that feed back on the clock, then on temperature directly.
On the other hand, you can entrain rhythms in reptiles with a 0.1 Celsius difference between the ‘cold’ and ‘warm’ parts of the cycle (my advisor showed that back in the late 1970s).
Also, there was a study on small mammals in the Arctic recently.
The mention of human reaction to the arctic night sounds interesting.
I’ve been coming down with a Winter depression (‘SAD’) this year after we came off Summer Time. Probably because I’m in the course of recovering from a ‘regular’ depression and still medicated and in therapy. I’ve only just acquired on of those fancy daylight lamps, so I’m hoping to see an effect.
Now, more ‘interesting’ is the fact that I’ve always been a ‘B-person’ or practically nocturnal at times (I used to joke that I functioned on New York time (I’m in Denmark)). At times I’ve found that if I really had to be up in the daytime it was far more efficient for me to skip a night and have a 26 h wake + 20 h sleep cycle — I even stuck to that for a coupla weeks at a time.
I’m kinda curious what I’d end up with if I was ‘stuck’ at either pole and not forced to follow an imposed 24 h schedule. How big is the need for depressive crystallographers who dropped out of their Ph.D. in Antarctica?
There are genes which enable the detection of moonlight.
From http://www.uq.edu.au/news/index.html?article=13238
Bugger.
That link should read http://www.solutions-site.org/artman/publish/article_356.shtml
It is still on topic, though.
What’s the variation of that “25-hour cycle” among individual humans? Is it closer to 25 +/- 0.5 hours, or 25 +/- 6 hours?
I’ve got a couple of comments on the relationship to tides.
1. Vancouver (I grew up there) and Newfoundland aren’t that close to the poles, so local topography is still going to dominate the size of the tides there. You have to get up to the arctic ocean to notice a real dropoff in the size of tides.
2. The tidal force is based on the amount that gravity drops off from one side of an object to another. The Earth is pretty big, so the tidal force is large enough to flex the rocks and move the water around.
On the other hand, people are a few times 10^6 times smaller, so the tidal force is extremely small. I would be very surprised if the human “25-hour” circadian rhythm is directly caused by the tidal force: that would mean that we have an amazingly sensitivity to tiny changes in force, and I’d really like to see some other tests of that idea. Also, what would be the evolutionary benefit of such a hypersensitivity to tidal force, when all it does is change your sleep cycle. This is particularly a problem given that much of early hominid evolution seems to have occured in environments that were a long ways inland from any major ocean.
So, as a non-biologist I’ll throw out a suggestion of my own for all of you folks who know that side of things a little better:
1. Perhaps this timing developed to correspond with moon phases? If early hominids were semi-noturnal, going out at night when the moon is full but not so much when the moon is closer to new, then their waking period might shift from day to night then back to day again throughout the month. I could certainly imagine that critters with our lousy night vision would not be too happy going about when the Moon wasn’t up, but finding it a lot safer when there’s some moonlight around to help out their feeble eyes.
Okay, any takers?
(#5 here again)
I have an old recollection of the report on the time deprivation study. Don’t think it was done on many subjects (it’s an inherently expensive experiment), and my recollection antedates recent concern about the ethics of experimentation (it’s no longer acceptable to vivisect the student at end of experiment.) So, #22, no idea of the standard deviation. Couldn’t find any cites via Google.
My idea is that many hominids were hunter-gatherers along the coastline, so a sense of tides could confer advantages that would be selected for [But then, why don’t we still have this sense at a conscious level?] My other idea is that homo sapiens did a lot of migration along the coastline, when the sea level was lower (e.g. Bering landbridge exposed), so many fossils evidence are underwater.
So there’s a few ideas in there for experts to chew over and spit out. It isn’t scientific until you run the experiments.
A possibly relevant datum is what I heard from Melissa Battler who spent a few months during the summer at the Mars Base simulation on Devon Island in the Canadian High Arctic. She & the other ‘astronauts’ spent some time using a sleep-wake cycle equal to the Martian day of 24 hours 39 minutes 35 seconds. They didn’t have any problems with that.
But more relevant to the arctic animals, tidal amplitude has much to do with the declination of the moon, which varies about 27 degrees north and south, and the sun declination. Resonances in local bathymetry affect tide height, a bit different from amplitude. So with Sun and moon at same 20 degree declination on a hypothetical smooth and spherical Earth, tidal effects at 80 degrees latitude match those at 40 degrees in the other hemisphere.
So if migratory birds can sense Earth’s magnetic field, maybe arctic lynxes can sense the tidal variation.
Should be someone out there smart enough to devise an experiment.
The physicist in me feels compelled to point out that the Sun does not go up and down on sidereal time. 24 hours it is.
dkary is on the ball. Tidal effects on small objects by large masses are miniscule.
From reading http://www.jal.cc.il.us/~mikolajsawicki/Tides_new2.pdf it would seem that the moon’s tidal effect on a human is enough to stretch a human less than one millionth the width of an atom. A pea held 0.5 metre over your head will have the same effect as the full moon (at its regular distance, of course). A lynx is smaller than a human, so the tidal effect on a lynx would be even more miniscule, and its ability to sense it concomittantly remote. I would doubt that the moon’s tidal effects alone could explain circadian cycles. I think that cryptochromes and moonlight could explain circadian rhythms better. An interesting test would be the examination of circadian cycles of subterranean mammals which do not use their eyes at all.
Furthermore, I have read that the fidelity of gene copying for an animal with a ‘disused’ organ is much reduced when compared with that of animals which still require the use of the organ. The genes for cryptochromes in such an animal would have many transcription errors if that is the case.
If our bodies are synchronized to the lunar schedule, then were still left with the same question as the original post. What happens when animals don’t get input needed to set our biological clocks? If humans use lunar clues, what happens to those not near large bodies of water with a lot of cloud cover? I suppose in the case of humans, we function by making tools that give us enough temporal structure.
IIRC, a day is, always was and will always be 24 hours. The time it takes the Earth to rotate the full 360 degrees around it’s axis, on the other hand, is about 23 hours and 56 minutes. Badastronomy.com explains the difference.
Great blog post. You’ve generated so many ideas, you have your life’s work cut out, trying to answer all the questions raised.
The circadian rhythms of adult humans, young and old, average about 24 hr 11 min (24.18 hr). The myth about 25 hr came from old studies where the subjects turned on the electric lights when they awoke and didn’t turn them off before they felt like going to bed. Humans being “higher beings” and not like animals, for heavens sakes, it was assumed that the extra self-regulated light in the evening wouldn’t delay their phases. The average human does delay a bit each day, if not corrected by daylight, but not by an hour.
(My blog, about Delayed sleep-phase syndrome, might interest you. I’m just a patient, not a doctor or scientist.)