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Tick Tock: the connection between celestial mechanics and genetics

The views expressed are those of the author and are not necessarily those of Scientific American.


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Astronomical Clock in Prague (Maros Mraz)

Sitting below the swirling leaves and darkening skies of New York today I realized that yet again our planet is roaring up on perihelion at 30 kilometers a second. This means that in about three weeks those of us in the United States will be shifting our clocks back an hour (after due reverence for the hallowed gorging on mass-produced sugar that has, believe it or not, pushed daylight savings a week into the future these past few years). The prospect of darker afternoons reminded me of a post from the Life, Unbounded archives back in January that I’ve put below.

Looking at this piece with hindsight I think that it suggests looking to see just how fast the biological clock can run, could it adjust to a 12 hour day? I’m sure others far more knowledgeable can fill in the blanks, but the idea of probing Earth’s dynamical history through genetics is intriguing.

Tick Tock

As those of us in the northern hemisphere of this small rocky planet contend with the winter nights and days it can feel like our internal clocks get a little out of whack. However, we and many other organisms actually have an extraordinarily robust built in timing mechanism that carries us through a roughly 24 hour cycle. Birds do it, bees do it, even educated C. Elegans do it. The circadian rhythm is something that may be a global property of terrestrial life. Regardless of sunlight then living things tend to operate on a daily routine, from rest to activity, and from high to low metabolic activity.

The exact biochemical origins of this internal clock have been somewhat elusive. In last week’s Nature two new works by O’Neill et al. shed some more light on the subject. A possibility has been that a transcription/translation feedback loop governing expression of certain ‘clock’ genes played a role in setting the 24 hour timer in organisms. O’Neill and colleagues seem to have found good evidence that there are additional, possibly superior, ‘time-keeping’ processes at play. In essence these are chemical ‘oscillators’ that behave like a well-tuned pendulum. Intriguingly this type of mechanism was already known to operate in the ancient cyano-bacteria. In tandem then perhaps both the purely chemical and gene mechanisms act like a self-correcting clock, keeping life to a consistent (roughly) 24 hour timetable. The genetic coding for the chemical clock seems likely to be shared amongst organisms like ourselves and ancient bacteria.

This is all very interesting. However, it also raises a number of questions that I’ve not seen discussed in detail in these or related experiments. 24 hours is the rotation period of the modern Earth. The Earth-Moon system has been in constant dynamical evolution since the formation of the Moon about 4.53 billion years ago following a massive proto-planet collision. At present the gravitational tides due to the Moon are dissipating energy at a rate of a few Terawatts and slowing the Earth’s rotation by about a couple of milliseconds a century. Other variations, like changing ice-caps, solar tides, even tectonic shifts tend to obscure this slowdown on short timescales but over millions of years there is little doubt that the Earth’s spin has been slowing. At the same time angular momentum conservation means that the Moon is receding from us at a few centimeters a year – a fact confirmed by laser ranging.

The upshot is that it’s quite possible that 4 billion years ago the Earth’s day-length was only 12 hours. Geological evidence is scarce to non-existent that far back, but studies of material deposited on what were once tidal shorelines indicate that around 600 million years ago the day length was certainly more like 22 hours, and the slowdown rate should have been more extreme in the further past. So the intriguing question to ask is how the biochemical clocks, be they the genetic or chemical variety, adjust over the millenia to that shift? Or, to be provocative, is there some way we could use our understanding of the evolution of these mechanisms to independently test the physical changes to Earth rotation over hundreds of millions to billions of years?

Celestial mechanics probed by paleogenetics? That sure sounds like fun.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. Bora Zivkovic 11:03 am 10/20/2011

    Awesome!

    I blogged about the O’Neill papers at length before which you may find interesting.

    First, in a 24 hours day, let’s say, your circadian clock can have a natural period anywhere between about 16h and 36h and still be entrainable by the 24h cycle (yes, farther your period from the environmental period, more malleable the clocks has to be, e.g., weaker coupling between the clock cells within a multicellular clock tissue, but that is pretty easy to modify by evolution). So small incremental changes in planet’s rotation do not have to have an immediate effect on the endogenous circadian period.

    Second, the rate of change of Earth’s rotation, even at times when it was relatively fast, geologically/cosmologically speaking, is still very slow compared to the rate of evolutionary change. In a few hundreds of millions of years, whole slews of species come and go, let alone small modifications of a couple of amino acids in a couple of clock proteins within any species. Thus, evolution will find it quite easy to track such slow changes. Not everything in evolution requires gazillions of years – many changes can occur in thousands of years if the selective pressure is strong, populations small, etc.

    Link to this
  2. 2. Caleb A. Scharf in reply to Caleb A. Scharf 4:04 pm 10/20/2011

    Great, thanks for the feedback! Will definitely read your post on the O’Neill papers.

    Link to this
  3. 3. Bora Zivkovic 4:39 pm 10/20/2011

    As for mechanism, at least in animals one can perhaps focus on the gene called ‘doubletime’ in insects (Casein kinase T in vertebrates) which modulates the period of the cycle of other core clock genes (e.g., period, timeless, etc.). Mutations in doubletime dramatically change circadiann period, in some cases doubling the frequency (halving the period). That is a potential site for fast evolution of the period.

    Of course, core clock genes themselves (e.g., Per) may be directly affected by selection. And even without any genetic changes, there is a phenomenon called ‘frequency demultiplication’ – which means that a 24h clock can get entrained by shorter (12h) or longer (any multiple of 24h) environmental cycles.

    Link to this
  4. 4. JDahiya 7:18 am 10/21/2011

    Why do so many people insist on resetting their rhythms twice a year? It’s bonkers. I hate having to check which day which country is going to do stupid things with their clocks, and all the scheduled meetings go for a toss.

    Link to this
  5. 5. dannyc 10:50 am 10/21/2011

    This paper was one of the many important papers from the Millar lab.

    The reason plants and animals have 24 hours clocks is the 24 hours light/dark cycle. The lengths of endogenous clocks are actually quite individual, which is why some of us “morning people” and some are “night people”. A plant’s clock can easily be entrained by a 6 hour light / 6 hour dark regimen to 12 hours. For example, if you look at plants that open their flowers in the day, and close them at night, under a 12 hours light cycle, they continue to open (albeit quickly) in the day and close in the very short night. But if you then put it back to constant dark or dim light conditions, it immediately reverts to its endogenous time keeper. With this huge plasticity, I wouldn’t worry too much about our planet slowing down. If we’re still around – we’ll adjust!

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  6. 6. Caleb A. Scharf in reply to Caleb A. Scharf 2:15 pm 10/21/2011

    So my dumb astrophysicist qn would be – if a plant’s clock can be entrained to a 12 hour cycle is there any way to ask whether this is a possible ‘ancestral’ characteristic – i.e. the flexibility is *because* (say) cyano-bacteria 3.5 billion years ago faced a true 12 hour day/night cycle and in the following time organisms have had to shift to the current 24 hour cycle. Or is this flexibility just ‘as is’ – perhaps with good evolutionary reason or perhaps just the nature of the time-keeping biochemical mechanisms?

    Link to this
  7. 7. BrainWorld 7:02 pm 10/21/2011

    Very interesting speculative article, it would be fascinating to find a genetic trace of clock changes due to changes in earth’s rotational period, but I am doubtful such a trace exists. It seems more likely that adaptations to longer day lengths have long ago ‘overwritten’ any such traces.

    You might be interested to know that in a graduate course in circadian rhythmicity I took in the 80′s I was taught that heavy water (deuterium oxide) ingested in human experiments disrupted the body’s clocks, essentially flatlining circadian variations in (I think) blood endocrine concentrations. This had an effect on test subjects like severe jet lag, making them quite uncomfortable. So uncomfortable in fact that more than one committed suicide. I doubt those results were published however. The takehome message is clear though: be careful about ingesting heavy water.

    In an earlier informal experiment I performed on myself as a grad student in a nutrition lab course, I went on a low-protein diet (limited to 45 grams protein daily plus or minus 5 grams when my normal intake had been 100 grams/day) to reduce my sweat rate. My low protein diet over two weeks worked dramatically well for that purpose but had the unexpected side effect of turning me from a night person to a morning person! This was a big benefit at the time because the lab class met at 8am and I went from terribly tired in the morning to bouncing into the lab with great energy and enthusiasm. Another guy in the course (males are rare in nutrition classes) who was a body builder had gone on a high protein diet for the assignment, and he experienced the opposite effect, dragging into class with bags under his eyes and saying he was so tired he couldn’t wait to be done with his experiment. As far as I know however, the effects of protein intake on circadian rhythmicity have not otherwise been scientifically studied.

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  8. 8. Bora Zivkovic 7:33 pm 10/21/2011

    Impossible to tell, but not impossible that 12h is ancestral, and frequency multiplication x2 happened later.

    Deuterium oxide is one of the rare chemicals to affect circadian rhythms, by increasing period (lowering frequency). I think this was originally done in a protist Gonyalax polyedra, and later in mammalian SCN cells in vitro. Other chemicals that can have an effect are lithium (which is why it works for bipolar disorder which is essentially a circadian disorder) and melatonin. Most other chemicals have no effect of period.

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  9. 9. Caleb A. Scharf in reply to Caleb A. Scharf 8:15 pm 10/21/2011

    Fascinating, thanks for the comments. I’d never heard of the deuterium oxide effect, how bizarre. I can only assume that’s just a chemical oddity rather than a pointer to anything deeper, given the rarity of concentration in nature.

    Link to this
  10. 10. dannyc 11:36 am 10/23/2011

    Great discussion.

    Just because the 1st bacteria probably arose 3.5 billion years ago doesn’t mean they immediately had evolved a clock. But even if so, I would guess the clock evolved along with changes in day length, with selection working towards what fit.

    Danny Chamovitz

    Link to this

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