Life in the Open Ocean. Joseph J. Torres

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Life in the Open Ocean - Joseph J. Torres


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for metabolic rates, it is imperative to also provide the temperature range over which the measurements were taken.

      In 1914, August Krogh, the father of comparative physiology, first attempted to define a pattern for the change in Q10 with temperature by subjecting a narcotized goldfish to temperatures ranging between 0 and 25 °C and measuring its oxygen consumption rate. The curve he derived is called the “Normal Curve.” It was popularized considerably in later years when it was found that a similar relationship between metabolism and temperature existed for many species, with the exception of the large Q10 in the 0–5 °C temperature interval (e.g. Winberg 1956). Even Krogh stated that his Q10 value of 10.9 between 0 and 5 was “obviously erroneous.” The general trend was remarkably accurate though, as were the numbers generated above 5 °C. The Q10’s this curve represents is shown below.

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      The Q10 approximation is a fundamental molecular response to temperature: it applies to chemical reactions taking place in a beaker as well as to rate processes in ectothermic species. However, it is not intuitively obvious why reaction rates should double for every increase in a temperature of 10 °C. The answer is in a concept termed “activation energy,” which was pioneered by the Swedish physical chemist Svante Arrhenius, and which earned him a Nobel Prize in 1903.

      In the realm of physical chemistry, temperatures are expressed in the absolute temperature scale, in degrees Kelvin. A Kelvin degree is equal to a degree Celsius, but the scale begins at absolute zero, the temperature where all molecular motion ceases: −273 °C. Thus, a temperature of 0 °C is equal to 273 K, and 20 °C is equal to 293 K; by convention, the degree symbol is not used for degrees Kelvin. The temperature range most relevant to the pelagic fauna, −2 to 40 °C (271–313 K), only covers about a 10% change of temperature on the absolute scale. In our range of concern, a change of 10 °C is roughly 3% of the absolute temperature. Why, then, do reaction rates double?

      Experimentation in the 1940s, 1950s, and 1960s further defined temperature responses as a function of time and acclimation period. Three general time courses were identified.

      1 Direct responses of rate functions to changes in temperature persisting for hours: acute measurements

Schematic illustration of energy distribution curves for a population of molecules at two different temperatures. Only those molecules having energies equal to or greater than the activation energy are reactive.

      Source: Hochachka and Somero (2002), figure 7.1 (p. 296). Reproduced with the permission of Oxford University Press.

      1 Compensatory acclimation to days or weeks of exposure: the acclimated response

      An animal is acclimated only when its rate processes have stabilized to the new temperature. Acclimated animals were utilized in constructing the temperature tolerance polygon shown in Figure 2.2a.

      1 Evolutionary adaptation through natural selection: climatic adaptation

      Patterns of Thermal Acclimation

       Type 4 acclimation: no change in rate occurs after time for acclimation (Q10 = 2–3).

       Type 2 acclimation: the animal’s rate falls or rises to original rate (Q10 = 1)

       Type 3 acclimation: somewhere in between (Q10 = 1–2)

       Type 1 acclimation: overcompensation – rate lower at higher temperature (Q10 < 0)

       Type 5 acclimation: reverse compensation (Q10 > 3)

Schematic illustration of Precht’s patterns of temperature acclimation.

      Source: Prosser (1973), figure 9‐13 (p. 375). Reproduced with the permission of Saunders Publishing.

      Climatic Adaptation in Ectotherms


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