RESUMO
Earthworms (Lumbricus terrestris) acclimated at 2 degrees C above their habitat temperature (10-12 degrees C) showed about 5% increase in basal rate of oxygen consumption, which increased to about 38% in 14-16 degrees C- and 40% in 16-18 degrees C-, but decreased by 84% in 20-22 degrees C-acclimated worms. Temperature also increased the blood hemoglobin (Hb) concentration, which decreased slightly in 20-22 degrees C-acclimated worms. The worms acclimated at 20-22 degrees C showed their blood to be hypovolemic than that of 10-12 degrees C worms indicating dehydration. Pre-exposure of 10-14 degrees C-acclimated worms to sublethal concentrations of zinc, copper, and lead did not significantly affect the rate of respiration. However, at higher temperatures all these metals inhibited oxygen consumption; zinc, lead, and cadmium by approximately 11% and copper by approximately 18% of that at 14-16 degrees C. At 20-22 degrees C, the respiration was further inhibited, 36% by copper, 18% by cadmium, and approximately 10% by lead and zinc. Copper, lead, and zinc decreased the temperature-enhanced increase in blood Hb concentration at all temperatures. In 20-22 degrees C-acclimated worms heavy metal exposure slightly lowered the oxygen affinity of Hb as well as caused shifts in carbon monoxide difference spectra. The acute toxicity of these metals was not affected by a 2 degrees C rise in acclimation temperature but increased by 17% (lead), 33% (copper), and 5% (zinc) in 14-16 degrees C- and by 40% (lead), 149% (copper), and 132% (zinc) in 20-22 degrees C-acclimated worms. The increase in toxicity of metals caused by high temperatures may be due to limiting the scope of aerobic metabolism (oxygen extraction, transport, and utilization) via quantitative and qualitative effects on Hb. This terrestrial species appears to be tolerant of slight increases in habitat temperature, such as that expected with current global climate change.
