Seems some correction is needed on the concepts of photoperiod.  I work for
DOT and have been involved in studies concerning shift work and time zone
change for air traffic controllers, pilots, truckers, and locomotive
engineers.  While I'm strictly versed in human reaction, both physical and
behavioral, I think much applies to the "lower" animals.  First, there are 2
types of photoperiods which are being treated as one.  There are circadian
rhythms (24 hr day) and seasonal (time of year) rhythms.  These have
distinctly different characteristics.
 
For example, the use of lights to further poultry growth by going to a
continuous day is a circadian effect.  Interestingly enough, in humans, the
major daily pituitary release of growth hormone occurs in the 1st hour of
sleep, so those all nighters stunt your growth, muscle development , and
immune response.  In environments lacking external cues to time of day, the
body "freewheels" and adopts a 25 hr day as the ideal.  Intriguing finding,
but no use of it yet.
 
For seasonal change, both the length of the day and the direction of change
are important.  This was inferred, but not stated explicitly.  How does the
body know if an equinox is spring or fall?  By the difference in day length
from the weeks before.
 
Seasonal and circadian rhythms have distinctly different effects, plus and
interaction.
 
>Obviously, it is not important _when_ the ferrets get their dark time; what
>is important is the _length_ of that time.
 
Not true, both are important.  To be more precise, it is the light time that
is important.  For circadian rhythms, recent findings at Brigham and Womens
Hospital have shown that exposure to very bright light for at least 20
minutes upon awakening resets the clock for the body.  Normally, no matter
what time you use as your wake up, your body functions remain in synch with
the sun.  This is how shift work disruptions occur, jet lag too.  This light
burst makes the body change time reference and allows it to work in concert
with wakefullness periods again.  The changes in disease resistance and
other health problems have been ascribed to disruption in circadian rhythm,
not seasonal.  So, light time timing does have an effect in people, and
probably ferrets too since this is a relatively primitive aspect.  What it
is in ferrets, I don't know, but it shouldn't be dismissed.  They do sleep
in such funny shifts
 
Some may be familiar with SAD (Seasonal Affective Disorder) where victims
become very depressed in the winter, correlated to latitude.  Here an
effective treatment found was to expose the person to bright light for
several hours each day, sort of a return to summer.  Seems the intensity of
light rather than just length or direction of change is effective on this
seasonal aspect.
 
The primary point of all this is to dispute the contention that artificial
light use has a harmful effect.  In humans, the controlled use of additional
artificial light has been shown repeatedly to provide benefits for both
circadian and seasonal problems.  I know of no study which indicates that
the light is harmful, nor is that concept really bandied about seriously.
(I do have a paper from a real crank that details the radiation dangers of
fluorescent lights that is a scream.  Unfortunately, I had to respond to it
as if it were credible.) On an anecdotal basis, humans have had artificial
light for a very long time, and as lighting has improved and lengthened, so
has lifespan.  Now I'm not so rash to ascribe that there is cause and effect
being demonstrated, most likely a chance correlation to other variables that
are really at work.  To assume that the reverse is true is poor science,
however.  I freely admit that none of this research is ferret specific, yet,
the mechanism comes to us from long ago in the evolutionary chain, the
"reptile" portion of the brain, in fact.  So all mammals share this.
 
I'm not in the "natural is best" camp as you may have noticed.  I believe
that understanding natural phenomena and using that knowledge intelligently
can improve life.  That is the basis for science and technology.  If you
disagree, let me know when you move back to a cave and drop from this list,
I'll study the results.
 
   ( )--(a)
   (@=@=) \     Till next time.......Rudy the ferlosopher
   O__)  \ \___
      \   \
      /\ * )  \
[Posted in FML issue 1608]