Thermal Acclimation and Compensation of Respiratory Oxygen Uptake in an Earthworm, Eisenia foetida

Abstract

Rates of respiratory oxygen uptake of Eisenia foetida acclimated at 15, 25, or 30 C were measured manometrically over a range of temperatures from 0 to 40 C. Whether rates of oxygen uptake were measured with a CO₂ absorber (KOH) or a CO2 buffer (Pardee solution), effects of temperature were essentially the same: Rates increased approximately linearly from 0 to 20 C. From 20 to 25 C there was a plateau, i.e., a range of thermal compensation with a Q10 of approximately one. From 25 to 35 C rates again increased; 40 C was lethal to most worms within 1 h. The partial pressure of CO2 in the gas phase influenced rates of respiration: Low concentrations stimulated oxygen uptake. Higher concentrations (0.4% and above) inhibited oxygen uptake. These effects of CO₂ concentration on respiration may be of evolutionary significance. The range of thermal compensation, i.e., the position of the plateau (2025 C), was not affected by temperature of acclimation. Rates of oxygen uptake in the range of compensation were influenced by acclimation temperature: they were lowest in 15 C– and highest in 30 C–acclimated worms. Thermal compensation appears to be an adaptive advantage for E. foetida, permitting these worms to remain active over a wider range of temperatures.