© 1979 by The Society for Integrative and Comparative Biology
Behavioral Thermoregulation and the "Final Preferendum" Paradigm
Department of Biology, The Pennsylvania State University Wilkes-Barre, Pennsylvania 18708
Wider attention to Fry's (1947) "final preferendum" paradigm would facilitate comparative studies of temperature preference (behavioral thermoregulation) among different animal groups. According to Fry's bipartite definition, the final preferendum 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 (acclimation). This paradigm is helpful in distinguishing between acute thermal preferenda (measured within 2 hr or less after placing an animal in a thermal gradient), which are influenced by acclimation temperature, and the species-specific final preferendum (measured 24–96 hr after placement in the gradient), which is essentially independent of prior acclimation 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 versus acclimation temperatures can be employed to determine an equivalent acclimation temperature 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 environments 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.