Figure 2

The effects of temperature on cardiac activity in porcelain crabs. Upper panel. Arrhenius plots of ln heart rate (beats per minute) versus measurement temperature (1/K) for two congeners of porcelain crabs, Petrolisthes cinctipes and P. eriomerus, having maximal habitat temperatures of approximately 32°C and 16°C, respectively. Arrhenius break temperatures (ABTs) are the temperatures at which a sharp decrease in heart rate is noted (see Stillman & Somero [9] for computational methods). Lower panel. Acclimatory-induced change in upper and lower critical temperatures (CT_max and CT_min, respectively) of heart function for 4 congeners of Petrolisthes: P. cinctipes and P. eriomerus from temperate central California habitats, and P. gracilis and P. hirtipes from the northern Gulf of California. CT_max is the ABT, and CT_min is the temperature at which heart beat ceased as temperature was lowered. Decreasing temperatures did not cause a sharp break in Arrhenius plots, so ABTs could not be determined at low temperatures [8,9]. Acclimation temperatures were 8°C and 18°C for the California species and 15°C and 25°C for the Gulf of California species. The differences in CT_max and CT_min between the two acclimation groups of each species are shown. Each symbol represents a different species, whose maximal habitat temperature is given on the abscissa. Figure modified after [8].