THERMAL ECOLOGY OF THE TREE AGAMA (AGAMA-ATRICOLLIS) IN ZAIRE WITH A REVIEW OF HEAT TOLERANCE IN REPTILES

Territorial behaviour and thermal ecology in relation to heat resistance in the tree agama (or black‐necked agama), Agama atricollis, were studied during two expeditions 1951–2 and 1958–9 in eastern Zaire (the former Belgian Congo) in an area just south of the equator. The maximum temperature tolerance of A. atricollis lies within the range of 43–43·9°C, but the maximum voluntary tolerance is somewhat lower, 42·5°C. Territorial males, retreating from their guard posts after having exposed themselves to direct sunlight during the hottest hours of the day for 10–16 minutes, reach body temperatures of 42·2–42·5°C before they retreat into the shade. In shady places it takes the males from 14 to 21 minutes to cool down to 38·1–39·9°C, at which body temperatures they return to the lookout within the territory. The territoriality in A. atricollis and several other species of the same genus, as well as other diurnal lizards with similar behaviour, may have contributed, through selection, to the evolution of their extraordinary resistance to substratum heat and direct sunlight. In an attempt to review and compare maximum voluntary body temperatures (MVT), critical thermal maxima (CTM) and lethal body temperatures (LT) in reptiles with pronounced heat resistance, data have been compiled for 96 species representing 11 families and six continents. The family Agamidae appears to be the most adapted to high body temperatures with 13 species (of 18 species tested) having body temperatures above 43°C in comparison with six species in Iguanidae (of 33 species tested), four in Gekkonidae (of nine species tested) and so forth. Agamids, iguanids, teeids and geckos, in hot environments of five continents, have evolved along the same lines behaviourally and physiologically as responses to territoriality in combination with high temperatures. This feature may be of adaptive significance. This paper also reports on body temperatures, obtained in Africa from free‐living individuals of seven other species of the genera Agama and Mabuya, namely A. atra, A. colonorum, A. hispida, A. planiceps, Mabuya quinquetaeniata, M. maculilabris and M. striata. Copyright © 1979, Wiley Blackwell. All rights reserved