Body temperature is a more pertinent variable to physiological stress than ambient air temperature. Modeling and empirical studies on the impacts of climate change on ectotherms usually assume that body temperature within organisms is uniform. However, many ectotherms show significant within-body temperature heterogeneity. The relationship between regional heterothermy and the response of ectotherms to sublethal and lethal conditions remains underexplored. We quantified within-body thermal heterogeneity in an intertidal sea star (Pisaster ochraceus) during aerial exposure at low tide to examine the lethal and sublethal effects of temperatures of different body regions. In manipulative experiments, we measured the temperature of the arms and central disc, as well as survival and arm abscission under extreme aerial conditions. Survival was related strongly to central disc temperature. Arms were generally warmer than the central disc in individuals that survived aerial heating, but we found the reverse in those that died. When the central disc reached sublethal temperatures of 31–35°C, arms reached temperatures of 33–39°C, inducing arm abscission. The absolute temperature of individual arms was a poor predictor of arm abscission, but the arms lost were consistently the hottest at the within-individual scale. Therefore, the vital region of this sea star may remain below the lethal threshold under extreme conditions, possibly through water movement from the arms to the central disc and/or evaporative cooling, but at the cost of increased risk of arm abscission. Initiation of arm abscission seems to reflect a whole-organism response while death occurs as a result of stress acting directly on central disc tissues.
↵† Present address: Marine Science Center, Northeastern University, Nahant, MA 01908, USA
All three authors contributed significantly to conception, design and execution of the study, interpretation of the findings, as well as drafting and revising the article.
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/12/2183/DC1
No competing interests declared.
This research was funded by grants from the National Aeronautics and Space Administration [NNG04GE43G to B.H.], the National Science Foundation [OCE-06-22924 to E.S.], and by a Lavoisier fellowship from the French Ministry of Foreign Affairs (2006-2007) to S.P.
- © 2013. Published by The Company of Biologists Ltd