[EAS]Non-24-Hr Circadian Rhythms

pjk pjk at design.eng.yale.edu
Thu Jul 12 19:03:32 EDT 2001

Subject:   Non-24-Hr Circadian Rhythms

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 547  July 12, 2001

Found almost ubiquitously in living organisms, circadian rhythms
are generated by body clocks with natural periods ranging roughly
from 22 to 28 hours.  However, they rarely match the 24-hour length
of a day (hence the word "circadian," meaning "about a day").  This
is strange, since species whose body clocks are resonant with the
Earth's 24-hour cycle of light intensity and temperature variations
ought to be the best ones for adapting to the environment and
organizing daily activities.  To address this issue, a physicist in
Japan (Hiroaki Daido, Kyushu Institute of Technology, now at the
University of Osaka Prefecture, daido at ms.osakafu-u.ac.jp,
011-81-722-54-9366) has devised a mathematical model that explores
competition between species with body clocks of different periods. 
Daido makes two major assumptions in his model: First, the
population growth rate of a species depends on the time difference
between its body clock period and the 24-hour day (for example, a
creature vulnerable to harmful ultraviolet rays during the day will
have a maximum growth rate if it has a 24-hour cycle and therefore
stays perfectly nocturnal). Second, the amount of competition
between pairs of species becomes more severe with a smaller time
difference between their body clocks (two species looking for food
will have an easier time if they do it 12 hours apart).  Daido's
model shows in particular that a 24-hour body clock can actually
turn out to be a disadvantage as long as the benefits of being in
sync with the environment are not large enough.  That's because
competition with other species turns out to be most intense for
species with 24-hour body clocks.  Daido's model can also address
other biological rhythms such as circannual rhythms which control,
for example, animals' hibernation timings.  However, he points out
that other factors, such as the effects of natural disasters, may
also have contributed to the existing circadian rhythms, and he
calls for testing the results of his model with biological
observations and experiments. (Daido, Physical Review Letters, 23
July 2001)

Those of you who know me personally (or even just watch the mailing
times of some of these EAS-INFO items) know how chronically
nocturnal I am. Even on (rare) days when I actually get up at say
8am, I have no difficulty staying up until 4am again.
I've long concluded that my circadian rhythm is considerably longer
than 24 hrs. It's also long been clear that I have no intention of
competing with species with 24-hr body clocks, and "two species
looking for food will have an easier time if they do it 12 hours
apart" certainly works fine for me with Web foraging.
Not being aware of any natural disasters that may have contributed
to my tardy body rhythm, I await Dr. Daido's further research with
curiosity.  --PJK

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