Relationship Between Respiratory Pumping and Oxygen Consumption in Aplysia Depilans and Aplysia Fasciata

Respiratory pumping in Aplysia is a well-characterized behaviour controlled by identified neurones, but its function is unknown. To gain insight into the function of this behaviour, respiratory pumping and oxygen consumption were examined under identical conditions, in Aplysia fasciata Poiret and in A. depilans Gmelin. A. fasciata is found in less turbulent environments than is A. depilans , suggesting that control of respiratory pumping may differ in the two species. Rates of respiratory pumping and oxygen consumption were poorly correlated. The basal rate of respiratory pumping was similar in both species and was not significantly dependent on animal mass, but the resting rate of oxygen consumption was higher in A. depilans than in A. fasciata and was an inverse function of animal mass in both species. Brief, moderate hypercapnia led to an increase in oxygen consumption in both Aplysia species . In A. fasciata , the increase was much greater. Increase in oxygen consumed was not accompanied by changes in the rate of respiratory pumping. Longer, more severe periods of hypercapnia led to decreases in oxygen consumption in both Aplysia species , and an increase in the rate of respiratory pumping. Decreased oxygen consumption was more gradual in A. fasciata . Severe hypoxia produced a decrease in the rate of oxygen consumed, and an increase in the rate of respiratory pumping.