Lecture Notes

Chilling Intolerance, Freeze Avoidance, Freeze Tolerance and the Ectotherm cooling curve.

  1. Diapause is not always a defense against cold. Could be defense against starvation in dry season.

  2. Insects overwinter in any stage of life (holometabolous insects have egg, larva, pupa and adult).

    1. Eastern tent caterpillar moth eggs overwinter.

      1. Embed themselves in webbing.
    2. Isabella tiger moth larvae have furry coat.

    3. Swallowtails overwinter as pupae

    4. Mourning cloaks overwinter as adults.

  3. Ectotherms have three responses to cold

    1. Chilling intolerance - must avoid cold as slight chill can be lethal. Freezes and dies a bit below melting point (supercooling point).

    2. Freeze avoidance - engage in supercooling and other behavior to avoid freezing as deep freeze can kill.

    3. Freeze-tolerance - Controlled freezing of body liquids. Less common.

  4. Ectotherm cooling pattern (Note the bump in temperature from the released heat during soldification.)

Freeze Intolerance/Avoidance

  1. Methods of freeze avoidance

    1. Overwinter in dry cavities

    2. Reduce body moisture

    3. Evacuate ice nucleators

    4. Bind water to other molecules.

    5. Thermal hysteresis proteins slow ice crystal growth.

    6. Polyols lower freezing and supercooling point.

  2. The Goldenrod Gall moth (epiblema) larvae causes galls, growths in trees. Lack plant defense compounds.

    1. The moth lowers its supercooling point well below the ambient temperature. Can lower to -40 degrees.

    2. Does this by shedding water and producing glycerol. Acts as antifreeze.

Freeze tolerance

1. Initiate ice formation in intercellular space, pulls water out of cells to prevent freezing. 

1. Organisms produce antifreeze (thermal hysteresis proteins and polyols). Slow freeze commences at higher temperature, avoids damage that flash freezing causes.
  1. Goldenrod Gall Fly (Eurosta) is freeze-tolerant, tolerates freezing of inside of cells.

  2. Glass Formation - Vitrification

    1. Red flat bark beetle (Cucujus) vitrifies, transforms fluids into glass to lower supercooling point. Makes organism dryer. Avoids damaging crystals.

    2. Glass-ice has lower heat capacity so with differential scanning calorimetry you can see dip where vitrification occurs. No exotherm is detected indicating no H2O solidification.

Organisms also use behavior to avoid cold.

  1. Freeze intolerant Belgica antarctica (Flightless midge) is in Antarctica, dies below -15 degrees C. Also dies if kept below +10 degrees C for a week. Survives by burrowing. Overwinters at all stages.

    1. Has the smallest genome.

Avoidance versus Tolerance

  1. Both use thermal hystersis proteins and polyols (antifreeze)

    1. Freeze avoiders increase supercooling range (difference between supercooling pooint and haemolymph (blood) melting point)

    2. Freeze tolerators reduce the range, initiating freezing at high temperature to slow freezing, dehydration and reorganization of cells to tolerate freezing.

  2. Irwin and Lee measured water loss and CO2 in supercooled Gall larvae, then froze them, then raised the temperature to measure the variables while frozen.

    1. Frozen gall flies use less energy and water (supercooling is thus metabolically costly).

    2. Lower winter temperatures reduce energy use. Elevated gall flies experience lower temperatures and make more eggs. Warmness on the ground causes ground flies to use more energy.

  3. Freeze avoidance (supercooling) is metastable.

    1. Ice can nucleate. Moisture can cause this. Internal nucleation is also a risk.

Colorado Potato Beetle

  1. Colorado potato beetles are not from colorado (originated in southern mexico) and potato was not their original host (buffalo bur was).

    1. Beetles emerge from treeline to colonize fields in the spring, and mate in the summer, then mate just before winter diapause.

    2. P flourescens bacteria has been used to nucleate ice in potato beetle to kill it. Raised supercooling point to -4.4 C on average. This is biological control, using organisms to control population.

    3. Problems

      1. Beetles are almost never going to experience -4.4 degrees C.

      2. How do you deliver the bacteria without killing non-potato beetles?

  2. Evolution of resistance to pesticide is slowed by costs of resistance. Possible reasons included with actual ones found to be culprits in bold.

    1. Fecundity lowering

    2. Mating competition, sperm competition.

    3. Overwintering success

    4. Immune function

    5. Movement

    6. Cannibalism

  3. A mate competition experiment

    1. If you irradiate some male beetles that emerge at a certain time (say, the fall), you can identify them as parents of offspring of females which mated with both them and spring males. So you can tell which sperm has precedence. Study on mate competition found there was no difference between hatch rates of beetles mating in isolated environment.

    2. Leaf cutter ant queens can live 27 years. Sperm gets stored for more than 20 years.

    3. If resistance is costly, less resistant males should be present in the Spring because they are worse at surviving. You can test this by giving fall sperm to some females and mating other females with groups of spring males. The spring-mated group should produce less resistant offspring because there are less resistant males, and this is what happens.

  4. Take homes

    1. Winter is a good way to manage resistance, because resistance is costly in winter.

    2. No sporaying being done, which involves relief from selection.

    3. Challenges of winter may reveal costs of resistance.

Vertebrate Ectotherms

  1. Same choice of freeze avoidance versus tolerance.

    1. But larger body size.
  2. Freeze tolerators risk:

    1. Cell-volume reduction

    2. Structural damage

    3. Protein denaturation

  3. Freeze avoiders (supercoolers) risk:

    1. Organismal dehydration
  4. Painted turtles have a bimodal strategy.

    1. Some freeze tolerant (50% frozen at -4 C), some freeze avoidant (supercool down to -15 C).
  5. Freeze tolerant vertebrates

    1. Wood frog

    2. Spring peeper

    3. Grey treefrog

    4. Painted turtle

    5. Snapping turtle

  6. Rapid Acclimation

    1. Wood frogs freeze over a 24 hour period. The start of freezing triggers a heat release, raising metabolism in the rest of the body, getting their bodies organized for further freezing.

    2. When there body is more than half frozen they lower their heartrate and go into frozen state.

  7. Cloacal respiration (breathing through the “anus”)

    1. found in hibernating and diving and river dwelling turtles.

    2. Spend up to 2 months submerged.

    3. Pulmonary respiration may be costly even with access to air.

    4. 70% of oxygen obtained by Australian river dwelling turtles.

Rapid Cold-hardening in insects

  1. Insects go into diapause well before it gets cold. However, some insects like a black fly, when pupae exposed to decrease from 25 to -10, do not emerge.

    1. But if held in between 25 to -10 transition at 0 degrees C for 2 hours, you get rapid cold acclimation/hardening.