1. Temperature Dependence

• Chemical reactions have an exponential dependence on temperature. So, metabolic rate (R) also has an exponential dependence on temperature (T).
  R/M = k 10^{(b T)}

• Notice that we can change this into a straight line by taking the log (to the base 10) of both sides of the equation: (Please note that equation 17-5 in Eckert is in error!)
  log(R/M )= log(k) + b T

• If we plot R vs. T, we do not get a straight line. However, the R vs. T relationship often looks linear over the relatively small temperature range that an organism can live. We can describe the slope of this approximate straight line given by plotting R vs. T, and thus the temperature dependence of metabolism, by comparing the metabolic rates at ten degree (C) intervals. This leads to the concept of the Q₁₀:
  Q₁₀= R_(T+10)/R_(T)

• Here we see a plot of R/M for a tiger moth caterpillar (Eckert, Fig. 17-2a) and the log plot (Eckert, Fig. 17-2b)

2. Acclimation - Biochemistry and physiology can change in response to new thermal conditions.

• We see that frogs can change body chemistry when the temperature drops for long periods of time, such as from summer to winter. We will discuss some interesting topics such as muscle biochemistry changes from summer to winter and how temperature changes affect the ability of the frogs to see in dim light! (Eckert, Fig. 17-3a)
• How do we explain acclimation?

  • Changes in enzyme structure (Eckert, Fig. 17-13)
  • Homeoviscous membrane adaptation - example: Rainbow Trout (Eckert, Fig. 17-4a) In heat, more cholesterol and more saturated fatty acids - why?
  • Production of more "heat shock proteins", also known as "molecular chaparones" In some marine intertidal snails, heat shock proteins are produced in greater numbers when temperature is increased and the cells are moved out of sea water into the air for 2.5 hours of exposure. (Eckert, Fig. 17-5) Note that T. brunnea is an intertidal species and has the ability to make a lot more shock proteins, a characteristic particularly useful for its ecological niche.

3. Endotherms and Ectotherms

• Endotherms generate their own heat and ectotherms rely on environmental sources of heat. All birds and mammals plus some terrestrial reptiles and a few insects are endotherms. (Eckert, Fig. 17-11)

4. Thermal Interaction with the environment

• Heat is transferred from the environment to animals or from animals to the environment in various ways - (Eckert, Fig. 17-6)
  • Conduction and Convection (Eckert, Fig. 17-7a) (Eckert, Fig. 17-7b) - countercurrent heat exchange (Eckert, Fig. 17-24) In the context of this discussion, you should read about the "rete" of the bluefin tuna in the Eckert textbook. A link that gives more information on the "rete" is here.
  • Radiation - Dragonflies and butterflies and basking reptiles. Plants orient their leaves too!
  • Evaporation - evaporation uses a very large amount of heat. In other words, changing water from liquid to vapor requires a lot of energy (to get the molecules jumping around enough). Example of the efficiency of cooling in DRY climates - evaporative coolers on houses in the desert southwest USA. The waterproof frogs -ectothermy at work!
  • Adaptations to cold: Some ectotherms, such as polar arthropods can avoid freezing by "osmotic depression of the freezing point". They can concentrate solutes such as sugars (glucose, fructose, trehalose) or sugar alcohols (glycerol, sorbitol, mannitol) and depress freezing point by as much as 10 degrees C. Many fish (ectotherms!) use "antifreeze proteins" to lower body temperature. These proteins are glycoproteins, often with a repeating peptide of alanine-alanine-threonin (what is the name for molecules such as alanine and threonin?) linked to a version of the carbohydrate galactose or an ordinary protein, lacking a carbohydrate moiety. Antarctic fish, such as the Icefish, Trematomus bernacchi, use such antifreeze proteins:
    
    Look here for more information on antifreeze proteins in Icefish
  • Adaptations to cold: Many animals can supercool - their temperature drops below normal freezing. If there is contact with ice crystals, the ice crystals serve as sites of nucleation and promote freezing of the water in the gills. But, if there is no such contact with ice crystals, the animal's fluids can often remain liquid even at temperatures considerably below the osmotically depressed freezing point. Some fish in the fjords of Labrador supercool. Frogs can supercool and some spiders can supercool by as much as 20 degrees below zero (C). The link above suggests that in Icefish, small ice crystals may be coated with antifreeze protein, which prevents such crystals from acting as sites of nucleation.

All text and images, not attributed to others, including course examinations and sample questions, are Copyright, 2008, Thomas J. Herbert and may not be used for any commercial purpose without the express written permission of Thomas J. Herbert.