Re: RE: Extinction

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

My apologies if this is drifting too far again.  Please holler at me
any time you think I should handle such things privately instead of to
the list.

Steve Grenard writes:

> My own Common horned lizards (aka "horfny toads"_ P. cornutum eat at
> between 95 and 105.  In my personal experience tgemperatures above
> 110 are lethal to horned lizards and all other desert reptiles. The
> statement that they wont feed at temps under 110 implies they will
> live and be happy at 110 and above. This is simply not correct.

I confess that my source for the temperature may not have been
terribly reliable.  I'll accept your claim that the lizards will feed
at lower temperatures.  I'm not so sure I'm willing to accept your
claims that 110 degrees F is so bad for desert lizards.  Where I used
to live in Arizona, daytime summer temperatures were usually over 110,
and occasionally well over 120.  While it's true that most lizards
tended to be more active in the morning (when the temperature was a
chilly 100) I could usually find lizards out and about at any time.

As for the frozen turtles, Steve states:

> While everything around their cells is frozen including their
> tissues, the cells remain very much nearly frozen but protected
> against freezing thanks to cryoprotectants.

No, the first part is is exactly what I was complaining about.  In
fact, I've just found another paper addressing the same issue.  I will
include the abstract to demonstrate the controversy that is still
bubbling here.  Note that I haven't read this paper in its entirety,
so I can't currently comment more on its content... Note also, that if
the controversy has been resolved, it likely has been resolved away
from the conclusion you state above.  Yes, the animals can survive
freezing temperatures (no debate there), but no, they do not
themselves freeze and still survive.

 Author(s):      PACKARD GC; PACKARD MJ
 Title:          THE BASIS FOR COLD TOLERANCE IN HATCHLING PAINTED TURTLES 
                   (CHRYSEMYS-PICTA) 
 
 Source:         PHYSIOLOGICAL ZOOLOGY V0068 N1 JAN-FEB 1995 pp. 129-148.
 Abstract:       Hatchling painted turtles (Chrysemys picta) overwintering in 
                   subterranean hibernacula may withstand exposure to 
                   temperatures as low as -11 degrees C. Some workers contend 
                   that this ability to survive in the cold results from a 
                   tolerance by the animals for freezing of water in the 
                   extracellular compartment, but other workers assert that 
                   hatchlings actually sustain a state of supercooling and 
                   remain unfrozen. We performed three experiments in the 
                   laboratory in an attempt to resolve this controversy. Fifty 
                   percent of hatchlings confined in artificial hibernacula in 
                   damp, clayey soil survived exposure to temperatures between 
-8
                   degrees and -9 degrees C, and some survived to near -11 
                   degrees C. Clean, dry turtles that were removed from contact
                   with ice survived in a supercooled, unfrozen state at 
                   minimum temperatures averaging -8.5 degrees C, so animals 
                   seem not to be at serious risk of freezing by spontaneous 
                   nucleation at temperatures spanning the range encountered in
                   nature. The integument in the axillary and inguinal pouches 
                   of hatchlings is highly conductive to ice, but skin on the 
                   extremities resists the penetration of ice into body 
                   compartments from the environment. By withdrawing their head
                   and limbs inside the shell and thereby removing skin of the
                   axillary and inguinal pouches from contact with ice, 
                   hatchlings generally were able to avoid inoculation and to 
                   survive in frozen soil at -26 degrees C for over 2 wk 
                   without freezing. However, a few animals experienced delayed
                   inoculation, and all these turtles died. Thus, hatchling 
                   painted turtles overwintering in the field probably 
                   withstand exposure to cold by undergoing supercooling and
                   not by tolerating freezing. 

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)