Woe is me: The life of an Antarctic worm

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Woe is me The life of an Antarctic worm

• Laura B. Vary
• EcoEvo 208
• October 24, 2005

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Sub-freezing Temperatures
sourcehttp//airs.jpl.nasa.gov/features/features_
newglobalmaps.html
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Antarctic Nematode

• Terrestrial Antarctic Nematode, Panagrolaimus
  davidi
• Experiences freezing temperatures over nine
  months of the year.
• During spring, experiences regular cycles of
  freezing and thawing
• Has both freeze-avoidance and freeze-tolerance
  strategies

sourcehttp//www.cep.aq/apa/aspa/sites/aspa147/ph
otographs/photo2.html
sourcehttp//www.rsnz.org/funding/marsden_fund/ne
ws27/index.phpantarctic
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Freezing avoidance strategy

• Cryoprotective dehydration
• When held at their nucleation temperature for a
  longer period, or when cooled at a slower rate,
  the nematode dehydrates instead of freezing.

source Wharton et al. 2003
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Mechanisms

• Osmotic stress
• As the medium freezes, salts become more
  concentrated in the unfrozen medium, creating
  osmotic stress for the worm
• Difference in vapor pressure
• With slower cooling rates, the water inside the
  worm is supercooled, thereby creating a vapor
  pressure difference between the ice in the medium
  and the worm.

source Wharton et al. 2003
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Freezing Tolerance Strategy

• P. davidi tolerates freezing at slower cooling
  rates better, but can also survive faster cooling
  rates
• A common effect of faster cooling rates, is
  intracellular freezing. P. davidi is the only
  animal known to survive ice crystallization
  within its cells (Wharton et al. 2005).

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Possible mechanisms

• Two important compounds
• Trehalose synthesized by nematodes in response
  to dessication and low temperatures. It is also
  known to act as a cryoprotectant in some animals.
• Recrystallisation-inhibiting protein P. davidi
  produces a protein that inhibits the activity of
  organic ice nucleators. The sequence of this
  protein has no homology with any other
  anti-freeze or ice-nucleating proteins.

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Nematode responses to environmental stress

• Hypothetical relationship of the response of
  nematodes to soil water content and freezing
  rate. As freezing rate increases and soil water
  content decreases, nematodes use different
  strategies.
• The final adaptation of anhydrobiosis occurs when
  no water remains in the soil and the nematode
  survives in this dormant state.

source Wharton 2003
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References

• Wharton DA, Goodall G Marshall CJ. 2003.
  Freezing survival and the cryoprotective
  dehydration as cold tolerance mechanisms in the
  Antarctic nematode Panagrolaimus davidi. J. Exp.
  Biol. 206 215-221.
• Wharton DA. 2003. The environmental physiology
  of Antarctic terrestrial nematodes a review. J.
  Comp. Physiol. B. 173 621-628.
• Wharton DA, Downes MF, Goodall G Marshall CJ.
  2005. Freezing and cryoprotective dehydration in
  an Antarctic nematode (Panagrolaimus davidi)
  visualised using a freeze substitution technique.
  Cryobiology. 50 21-28.