EFFECT OF TEMPERATURE ON SURFACING BEHAVIOR IN XENOPUS-LAEVIS

1. The surfacing frequency of X. laevis increased with temperature from 1 to 6 h(-1) between 5 and 20 degrees C, either by day or night, but was unchanged between 20 and 25 degrees C. 2. The duration of individual visits to the surface was relatively short (10-40 s) and unaffected by temperature below 20 degrees C during the day but increased markedly to over an hour when temperature was reduced from 20 to 5 degrees C during the night. The duration of each visit increased when temperature was raised from 20 to 25 degrees C during the day or night. 3. Consequently, the proportion of total time spent on the water surface by the toads increased with temperature (2-12%) during the day; whereas during the night, total time at the surface was highest at 5 degrees C (50%), lowest at 20 degrees C (14%) and higher at 25 degrees C (30%). 4. The brief visits to the water surface during the day are probably driven by oxygen demand or the accumulation of CO2. At night, when predation pressures may be reduced, the toads spend more time at the surface.