Behavioral thermoregulation and the "final preferendum" paradigm

  • Reynolds W
  • Casterlin M
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Wider attention to Fry's (1947) "final preferendum" paradigm would facilitate comparative studies of temperature preference (behavioral thermoregulation) among dif- ferent animal groups. According to Fry's bipartite definition, thefinal preferendurn is that temperature at which preference and acclimation are equal, and to which an animal in a thermal gradient will finally gravitate regardless of its prior thermal experience (acclima- tion). This paradigm is helpful in distinguishing between acute theml prefer& (mea- sured within 2 hr or less after placing an animal in a thermal gradient), which are influ- enced by acclimation temperature, and the species-specificfinal preferendurn (measured 24-96 hr after placement in the gradient), which is essentially independent of prior accli- mation because reacclimation occurs during the gravitation process. The paradigm does not take into account non-thermal acclimatization influences (e.g., season, photoperiod, age, light intensity, salinity, disease, nutrition, pollutants, biotic interactions) which can also affect temperature preference. However, a graph of acutely preferred temperatures vmsw acclimation temperatures can be employed to determine an equivalent acclimation tempera- ture for any given acclimatization state, as a simple means of quantifying acclimatization states resulting from interactions of many influences. This paradigm, developed for use with fishes, can also be applied to other ectothermic taxa, although it is most easily employed with aquatic organisms because of the simplicity of specifying aquatic thermal environ- ments in terms of water temperature alone. Methodologies used in studies of behavioral thermoregulation should take the paradigm into account (especially with respect to length of tests) to enhance the comparative value of data across taxa.

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  • William Wallace Reynolds

  • Martha Elizabeth Casterlin

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