Physiological responses to temperature and haeme synthesis modifiers in earthworm Lumbricus terrestris (Annelida: Oligochaeta)

Earthworms (Lumbricus terrestris) acclimated at 2° and 6°C above their average habitat temperature (10°C) had respectively 15 and 40% higher rate of respiration than those at habitat temperature. At 14°C, the rate of respiration and blood hemoglobin (Hb) concentration both increased by ∼60 and 50%, respectively, of the values at habitat temperature. At higher temperatures the rate of respiration and Hb synthesis started decreasing. At 20-23°C, the respiration and Hb concentration decreased respectively by about 85% and 35% of that at 14°C. Decrease in blood Hb concentration at higher temperatures appeared to be due to the lowering of the activity of blood enzyme δ-aminolaevulinic acid dehydratase (ALAD). Exposure of 20-23°C-acclimated pale worms to ALAD inhibitor (lead), lowered the already compromised rate of respiration and blood Hb concentration; while exposure to hexachlorobenzene (HCB, inducer of haeme synthesis) and ferric chloride (enhancer of haeme synthesis) did not overcome the inhibitory effect of high temperature on Hb synthesis. At 20-23°C the affinity of Hb for oxygen also decreased as indicated by the lowering of oxy-Hb (HbO) concentration in blood. The lowering of concentration of blood Hb and its affinity for oxygen may lower the amount of oxygen delivered to cells, which may limit the level of aerobic metabolism (glycolysis, oxidative phosphorylation), as indicated by an increase in blood glucose concentration and a decrease in in vitro activities of mitochondrial electron transport system components (ETS) namely NADH-cytochrome c reductase, succinate dehydrogenase, cytochrome c oxidase, and ATPases. Although the oxygen concentration in air, at sea level, does not decrease significantly from 6° to 20-23°C (lack of hypoxia), lowering of both Hb and HbO concentrations by high temperature may cause significant hypoxemia. The latter may lead to inhibition of the activity of muscle mitochondrial respiratory enzymes (ETS). The resulting inhibition of ATP synthesis and hydrolysis may cause deficit of energy needed for peristalsis/fictive locomotion of body and heart muscles (as indicated by a decrease in heart rate) to facilitate diffusion and transport of gases. The upper critical temperature (20-23°C) also slows down the heart rate and causes hyperosmotic stress (hypovolemia). Thus, a rise in soil temperature above 18°C, which inhibits Hb synthesis, Hb oxygenation, and mitochondrial ETS activity, and slows down the heart rate and causes hyperosmotic stress, can make this and higher temperatures lethal to populations of these earthworms, especially in the presence of metabolic inhibitors and respiratory poisons.

Effect of temperature on heavy metal toxicity to earthworm Lumbricus terrestris (Annelida: Oligochaeta)

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.

Effect of temperature on heavy metal toxicity to juvenile crayfish, Orconectes immunis (Hagen)

The acute toxicity of four selected heavy metals to juvenile crayfish Orconectes immunis (Hagen) (1-2 g wet body wt. each) at room temperature increased in the following order: cadmium (x3) < copper (x10) < zinc (x2) < lead. The toxicity of these metals to crayfish acclimated at 17, 20, 23/24, and 27 degrees C increased with temperature (by 7-20% between 20 and 24 degrees C and 14-26% between 20 and 27 degrees C) as judged by the lowering of LT(50) (time to kill 50% of test animals at a fixed concentration) values. A 4 degrees C rise in temperature (from 20 to 24 degrees C), which increased the toxicity of copper by about 7%, increased the rate of oxygen consumption by about 34%. Heavy metals inhibited the rate of oxygen consumption at all temperatures. In 20 degrees C-acclimated crayfish, copper caused about 17% inhibition of oxygen consumption compared to about 7-12% by other metals including the most toxic cadmium. A 3-4 degrees C rise in temperature tripled the inhibitory effect of copper (20%), cadmium and zinc (26 and 18%, respectively), but not of lead, on oxygen consumption. A 7 degrees C-rise in temperature (from 20 to 27 degrees C) increased the inhibitory effect of heavy metals, including lead, on oxygen consumption by up to 54% in the case of copper. The data indicate that rising global temperatures (currently 0.60 degrees C) associated with climate change can have the potential to increase the sensitivity of aquatic animals to heavy metals in their environment.