The thermodynamic dependence of physiological functions on temperature means that rate processes will fluctuate with environmental fluctuations unless rates are buffered by compensatory responses, or body temperature is regulated in spite of environmental variability. Contrary to the prevailing dogma, even animals that regulate their temperature show significant plasticity at all levels of organisation to compensate for temperature induced decreases in performance and/or increased costs of behavioural thermoregulation in cooler conditions.
For example, swimming performance (Ucrit) of crocodiles acclimates perfectly to different temperatures (Fig. 1 left panel), and concomitantly ATP production in mitochondria becomes more efficient (respiratory control ratio, Fig. 1 right panel). At the same time, the expression of key metabolic and regulatory genes changes in response to different acclimation temperatures (Fig. 2).
Hence, the capacity for phenotypic flexibility should be tested as a null-hypothesis (Fig. 3) before conclusions can be drawn about adaptive responses or ecological consequences of microhabitat choice or climate change.
Seebacher, F., and James, R. S. 2008. Plasticity of muscle function in a thermoregulating ectotherm (Crocodylus porosus): biomechanics and metabolism. American Journal of Physiology Regulatory, Integrative and Comparative Physiology 294, 1024-1032.
T. S., Murray, S. A., and Seebacher, F.
2008. Novel reptilian uncoupling proteins: molecular
evolution and gene expression during cold acclimation. Proceedings
of the Royal Society
Schnell, A. K., and Seebacher F. 2008. Can phenotypic plasticity facilitate the geographic expansion of the tilapia Oreochromis mossambicus? Physiological and Biochemical Zoology 81, 733-742.
Glanville, E. J., and Seebacher, F. 2006. Compensation for environmental change by complementary shifts of thermal sensitivity and thermoregulatory behaviour in an ectotherm. Journal of Experimental Biology 209, 4869-4877.
Seebacher, F. 2005. A review of thermoregulation and physiological performance in reptiles: what is the role of phenotypic flexibility? Journal of Comparative Physiology B 175, 453-461.
Seebacher, F., Davison, W., Lowe, C. J., and Franklin, C. E. 2005. A falsification of the thermal specialization paradigm: compensation for elevated temperatures in Antarctic fish. Biology Letters 1, 151-154.
Seebacher, F., Guderley, H., Elsey, R. M. and Trosclair, P. L. III. 2003. Seasonal acclimatisation of muscle metabolic enzymes in a reptile (Alligator mississippiensis). Journal of Experimental Biology 206, 1193-1200.