Heart rate response to gentle handling of frog and lizard.

Heart rate was counted telemetrically in lizards (Iguana iguana) and frogs (Rana catesbeiana and Rana pipiens) to estimate their response to gentle 1-min handling. The animals were kept at steady body temperatures of ca. 28 degrees C (lizards), and 24 degrees C (frogs). Handling increased the heart rate of lizards from ca. 70 to 110 beats per min immediately during and after handling and this tachycardia decreased in ca. 10 min. Similar handling did not modify significantly the frogs' heart rates. Although the absence of a response to mild stress is not synonymous with the absence of emotion, the absence of handling-tachycardia in frogs and its presence in lizards (as well as in mammals and birds), together with the emotional fever in mammals, birds, and reptiles, but not frogs or fish as reported in the literature, might suggest that 'emotional' response to stress emerged in phylogeny between amphibians and reptiles.