OXYGEN-CONSUMPTION, HEART-RATE AND RESPIRATORY MOVEMENTS ARE MAINTAINED ALMOST UNCHANGED IN TOADS (BUFO-VIRIDIS) ON SOIL WITHOUT ACCESS TO FREE-WATER

The terrestrial toad Bufo viridis was maintained on soil (12-14% water content) without access to free water for periods lasting over 10 wee ks. The weight of the animals stabilized after some loss of water (15- 25%) which was accompanied by a large increase in plasma osmolality (f rom about 400 to 950 mOsm kg(-1) H2O). Oxygen consumption of toads kep t on soil for over 4 weeks was 3.39 +/- 0.29 ml h(-1) (mean +/- SE of 10 toads weighing 35.8 +/- 2.6 g), which was lower by about 15% as com pared to control, water-access conditions. Rate of respiratory movemen ts and heart rate were quite variable, and were similar in control con ditions and on soil without free water. A Q(10) of 1.8 was calculated for heart rate over a temperature range of 10-30 degrees C. Acute dehy dration (15% in 24h) resulted in a small (10%) but insignificant incre ase in the heart rate. It is concluded that active Bufo viridis on soi l, in water restricted condition, maintains its aerobic metabolism at a level that is reduced by no more than 15-25% of the control, despite large changes (more than doubling) in the osmolality and composition of its body fluids. (C) 1996 Academic Press Limited