Discontinuous Carbon Dioxide Release and Metabolic Depression in Dormant Land Snails

Abstract

The respiration of dormant land snails (Otala lactea Müller) is characterized by periodic retention and release of CO2. Rates of oxygen uptake (VOO2) and CO2 release (VCOCO2) of individuals were recorded continuously for up to 21 days. VOO2 was usually low (5.6 μlg-1 tissueh-1) but increased up to five-fold at intervals between 20 and 50 h. Snails hypoventilated and retained CO2 when VOO2 was low, while periods of elevated VOO2 commenced with hyperventilation and net CO2 release. The ratio VCOCO2/VOO2 varied between about 0.2 and 4.8 during these cycles. Calculated wholebody CO2 content fluctuated over a range of about 4.3 mmoll−1 H2O, and was inversely correlated with VOO2. Cycles of CO2 retention and release might be the result and/or the cause of changes in metabolic rate during dormancy. Ventilation is sensitive primarily to O2, and O2 transport appears to be diffusion-limited. A simple model based on these characteristics predicts hypoventilation and consequent CO2 retention when VOO2 is reduced. Also, the close correlation of VOO2 and whole-body CO2 content in snails suggests that CO2 or acid-base balance might influence metabolic rate during dormancy. The relationship between discontinuous CO2 release and respiratory water loss in insects and snails is discussed.