The critical thermal maximum: history and critique

Abstract

We reviewed 725 papers published since Cowles and Bogert's paper on thermal tolerance (R.B. Cowles and C.M. Bogert. 1944. Bull. Am. Mus. Nat. Hist. 83: 261–296) to create a data base of studies that used critical thermal maximum or lethal-temperature methods. We found data from 388 of these papers to provide a historical and taxonomic review of various methodologies used in measuring tolerance of high temperature. We conducted this literature review of previous studies to (i) describe the history of the study of thermal tolerance and show the chronological trends in the use of lethal temperature and critical thermal maximum methods, (ii) illustrate the diversity of taxa used in thermal-tolerance studies, (iii) summarize the diversity of protocols (i.e., end points, heating rates, acclimations, etc.) used for determining thermal tolerance, (iv) provide physiological reasons why the onset of spasms is more meaningful biologically than the loss of righting response, and (v) discuss the difficulties in using data from studies in which widely divergent methods were used and the importance of obtaining comparative thermal-tolerance data for comparative physiology. The adoption of the onset of spasms as a standard end point would allow for valid comparisons of data from different studies and among taxa, an important consideration for current investigations of comparative physiology that use the comparative phylogenetic method.

Effect of warming rate on the critical thermal maxima of crabs, shrimp and fish

“…This would be of great value for inter-specific comparisons. Becker and Genoway (1979) recommended 0.3°C min À 1 , Lutterschmidt and Hutchison (1997) recommended 1°C min À 1 and, more recently, Mora and Maya (2006) suggested 1°C h À 1 .…”

“…It has also been applied in macrophysiological comparative studies in ectotherms (e.g. Lee and Boulding, 2010;Cowles and Bogert, 1944;Lutterschmidt and Hutchison, 1997) and in the exploration of upper thermal tolerances across different taxa (Somero, 2005(Somero, , 2010Deutsch et al, 2008).…”

“…Dynamic methods have many advantages over static methods. They require fewer animals and experiments are faster (Lutterschmidt and Hutchison, 1997), because static metrics, such as the temperature that causes 50% of mortality, or lethal temperature, is determined from a plot of percent mortality at given temperature intervals. Another important advantage of the CTMax method, in particular, is that it is sublethal, rather than lethal, and thus provides a reference for temperature tolerance that takes into account a more conservative thermal limit in which the organism does not die but is unable to escape predators and forage because of equilibrium loss.…”

“…This rate has varied widely among published protocols, from 10°C min À 1 to 1°C 48 h À 1 (reviews in Lutterschmidt and Hutchison, 1997;Mora and Maya, 2006). Fast warming rates can result in a long lag between the experimental temperature and the internal temperature of the individual, overestimating the upper thermal limit (Becker and Genoway, 1979;Lutterschmidt and Hutchison, 1997). Slow warming rates may allow the individual to acclimate, also overestimating the upper thermal limit, or allow temperature to exert its lethal effects and, in that case, underestimating the thermal limit (Cocking, 1959;Beitinger et al, 2000).…”

Thermal physiology of the common eelpout (Zoarces viviparus)

“…Therefore, the value of CTMax depends on the experimental protocol (rate of temperature increment and acclimation temperature). The heating rate of 1°C min -1 was chosen according to Lutterschmidt and Hutchison (1997b), because with a faster protocol (>1°C min -1 ), lag-periods between changes in body and water temperature may interfere. On the other hand, a slower protocol (<1°C min -1 ) might result in the interference of acclimation effects (for instance, changes in protein synthesis).…”