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Evolutionary and Ecological Physiology |
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Phenotypic Plasticity
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).
Fig. 1 Sustained swimming performance
(Ucrit, left panel) and mitochondrial respiratory control ratio (right
panels) of the crocodile (Crocodylus
porosus) changed significantly with thermal acclimation.
Fig. 2 Gene expression of the metabolic
coactivator pgc1" in response to thermal acclimation of the crocodile (Crocodylus porosus). 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.
Fig. 3 Experimental designs in thermal biology should incorporate the capacity for phenotypic flexibility, with the null hypothesis that observed differences between populations or between individuals at different microhabitats are reversible. 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. Schwartz,
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.
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