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Physiological responses to temperature reflect the evolutionary adaptations of organisms to their thermal environment and the capability of animals to tolerate thermal stress. Contrary to conventional metabolism theory, increasing environmental temperatures have been shown to reduce metabolic rate in rocky-eulittoral-fringe species inhabiting highly variable environments, possibly as a strategy for energy conservation. To study the physiological adaptations of an intertidal-subtidal species to the extreme and unpredictable heat stress of the intertidal zone, oxygen consumption rate and heat shock protein expression were quantified in the sea cucumber Apostichopus japonicus. Using simulate natural temperatures, the relationship between temperature, physiological performance (oxygen consumption and heat shock proteins) and thermotolerance were assessed. Depression of oxygen consumption rate and upregulation of heat shock protein genes (hsps) occurred in sequence when ambient temperature was increased from 24 to 30°C. Large-scale mortality of the sea cucumber occurred when temperatures rose beyond 30°C, suggesting that the upregulation of heat shock proteins and mortality are closely related to the depression of aerobic metabolism, a phenomenon that is in line with the concept of oxygen- and capacity-limited thermal tolerance (OCLTT). The physiologically-related thermotolerance of this sea cucumber should be an adaptation to its local environment.
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22022615
???displayArticle.pmcLink???PMC3195708 ???displayArticle.link???PLoS One
Figure 2. The two-stage segmental regression of the peak values ofhsp70 and temperature of sea cucumber, Apostichopus japonicus in intestine, respiratory trees and body wall.
Figure 3. The two-stage segmental regressions of the peak values of (a) hsp90a and (b) hsp90b and temperature of sea cucumber Apostichopus japonicus in intestine, respiratory trees and body wall.
Figure 4. The variation trend of expression of hsps, oxygen consumption rate and specific growth rate (SGR) with temperature increase in the sea cucumber Apostichopus japonicus.Pejus temperature (Tp), which is the limit of optimum hemolymph oxygenation and therefore temperatures above this will result in a worsening of oxygen supply to the organism; critical threshold temperatures (Tc) where the mitochondrial metabolism transforms to an anaerobic mode (Reference 28). The specific growth rate (SGR) data are cited from previous studies (references 16, 18), and the temperature lethal to 50% of the samples (TL50) after 2 h exposure was cited from reference 19.
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