Heat tolerance,temperature acclimation,acute oxidative damage and canalization of haemoglobin expression in <Emphasis Type="Italic">Daphnia</Emphasis> |
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Authors: | Patricia J Williams Kenneth B Dick Lev Y Yampolsky |
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Institution: | (1) Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37614-1710, USA;(2) Present address: School of Natural Sciences, Lenoir-Rhyne University, Hickory, NC 28603, USA; |
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Abstract: | Daphnia is a widespread freshwater zooplankton species, which is both a classic and emerging new model for research in ecological
physiology, ecotoxicology and evolutionary biology of adaptation to novel environments. Heat tolerance in Daphnia is known to depend both upon evolutionary history of a genotype and on individuals’ acclimation to elevated temperature and
to correlate with the level of haemoglobin expression. We demonstrate the existence of north–south gradient of heat tolerance
in North American D. pulex, which is not associated with any parallel changes in haemoglobin expression. Geographically distinct clones differ in the
way their haemoglobin expression changes due to acclimation to a sub-stressful (28°C) temperature, but these changes are not
correlated with the latitude of clones’ origin. Likewise, the effect of acclimation to sub-stressful temperature is independent
from, and cannot be fully explained by, haemoglobin expression changes during acclimation. The degree of oxidative damage
to haemoglobin, measured as the ratio of absorbance at 540:576 nm at the acclimation temperature, is a strong predictor of
28°C-acclimated Daphnia survival during an acute heat exposure. The comparison of haemoglobin expression in resistant and tolerant clones acclimated
to different temperatures indicates that tolerant clones exhibit canalization of haemoglobin expression, possessing a high
level of haemoglobin even at non-stressful temperatures. We discuss the evolutionary biology of adaptation and acclimation
to elevated temperatures in an ecologically important component of freshwater ecosystems in the context of global climate
change. |
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