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FREEZE TOLERANT VERTEBRATES
Wood Frog
These
are some of the terrestrially-hibernating, freeze tolerant amphibians and
reptiles that we work on in the Storey lab.
See pictures
below
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Amphibians |
Reptiles |
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Wood frog (Rana sylvatica) |
Painted turtles (Chrysemys picta) |
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Gray tree frog (Hyla versicolor) |
Box turtles (Terrapene |
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Spring peeper (Pseudacris crucifer) |
Garter snakes (Thamnophis sirtalis) |
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Chorus frog (Pseudacris triseriata) |
European
common lizard (Lacerta vivipara) |
For
cold-blooded terrestrial vertebrates, exposure to temperatures below 0°C (32°F)
presents a serious problem because the freezing point of their blood is about -0.5°C.
Many animals avoid the risk of freezing by retreating underwater to hibernate
(e.g. leopard frogs, bullfrogs, many turtles) or by going deep underground,
either digging in by themselves (e.g. toads) or by using rodent tunnels or
natural caves (e.g. salamanders, snakes).
But
other amphibians and reptiles hibernate at or near the soil surface where
temperatures can drop substantially below the freezing point of their body
fluids. These have developed the amazing ability to endure the freezing of water
in extracellular body compartments. As much as 65% of their total body water
may be converted to ice and they can survive days or weeks of freezing.
Click to link to VIDEO, AUDIO and PRINT INTERVIEWS
from the STOREY LAB and other popular information about frozen frogs
Click to link to
go to
scientific review articles and encyclopedia entries written by the STOREY
LAB: both popular and detailed science
For an easy-to-read general article
about Animal Cold Hardiness, also see PDF
COOL LINKS to
other sites:
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FROZEN ALIVE - pics and info on frozen frogs at NatureNorthZine |
Wood frogs in the classroom and rearing tadpoles from NatureNorthZine |
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Frozen frogs at the |
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LIFE STYLES OF THE COLD AND FROZEN - The Sciences magazine, 1999 Full Article |
Frozen frogs in HISTORY, 1746-1849. |
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Frozen
TURTLES: Out cold - The winter life of
painted turtles. Natural History magazine, 1992 Full Article |
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WOOD FROGS, Rana
sylvatica
These are the best studied
of all freeze tolerant vertebrates. Wood frogs breed very early in the spring in
ephemeral forest ponds (see our favourite pond) and their eggs and tadpoles need to develop quickly before
the ponds dry out. By hibernating on the forest floor, wood frogs can emerge with
the melting snow and take immediate advantage of melt-water ponds for breeding.
Wintering at the soil surface, the frogs gain significant insulation from
blankets of leaf litter and snow but temperatures in their microhabitat still
range down to -8°C at times.
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Picture 1 Wood frog |
Picture 2 – many color morphs |
Picture 3 – characteristic black mask |
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Picture 4 |
Picture 5 – juvenile, autumn of 1st
year |
Picture 6 – bucket of frogs |
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Picture 7 Frozen wood frog |
Picture 8 |
Picture 9 |
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Picture 10 |
Picture 11 |
Picture 12 |
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Picture 13 |
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As frogs freeze, they
assume a crouched position with limbs drawn in close to the body and often digits
tucked underneath. This position is known as the "water-holding"
position and is used by all frogs when under desiccation stress. For frozen
frogs this helps to reduce evaporative water loss from the body over what
could be weeks of continuous freezing. Frozen frogs have no heart beat, no blood circulation, no breathing, no detectable brain activity and cannot move yet miraculously all vital functions return within 1-2 hours when frogs thaw. |
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GRAY TREE
FROG, Hyla versicolor
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Picture 14 |
Picture 15 |
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Picture 16 |
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These are intriguing fellows. They have the ability to
change color, ranging from mottled gray through to lime green. When frozen, they turn blue. |
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Picture 17 Frozen |
Picture 18 |
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FREEZE TOLERANT REPTILES
Picture 19 Painted
turtle hatchlings Chrysemys picta |
Picture 20 Western
subspecies, |
Picture 21 Midland
subspecies, |
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Although painted turtles
hatch from their eggs in September, they do not leave their nests on lake and
river banks until the next spring. To survive the winter, hatchlings have
developed freeze tolerance. Adults have another remarkable ability -- they
winter underwater and can survive for 3-4 months without breathing oxygen
while in ice locked ponds. Link to our Anoxia Tolerance site.
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Picture 22 A-D Painted
turtles spend their first winter in the natal nest. They push out of their shells
and sit in a heads up position. In the spring, they get active, dig out of
the nest and head for the nearest body of water. The
sequence shows one hatchling exiting the nest. A couple of pieces of empty
shell can also be seen. |
A |
B |
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C |
D |
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Picture 23 Garter snake |
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Garter snakes winter
underground, often massing by the hundreds in huge dens where temperatures
rarely drop below 0°C. Their tolerance to freezing is pretty minimal - up to a
day at -1.5°C but only a few hours at lower temperatures. However, this
capacity might help them to survive unexpectedly cold nights in the spring or
autumn. Alternately, detection of freezing within the den may stimulate them
to move to warmer spots. Read about Garter Snakes in the Classroom and the annual Narcisse snake
log at NatureNorthZine. Read more about the
garter snakes on the U Haul website
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Picture24 Box turtle |
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Box turtles are the largest known freeze tolerant animal, ranging up to about 1 kg body weight. They hibernate in shallow burrows and probably don't encounter freezing conditions too often but we've documented survival after 2 days frozen at -2°C. |
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Picture 25 European common lizard |
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The European common
lizard is one of the few |
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