The Function of Haemoglobin in Relation to the Maintenance of Neutral Buoyancy in Anisops Pellucens (Notonectidae, Hemiptera)

ABSTRACT The percentage saturation of the haemoglobin of the intact water bug, Anisops pellucens, in equilibrium with various ambient oxygen tensions has been determined. From this an approximate dissociation curve for the pigment and a P50 value of 28 mm. Hg at 24 ° C. have been obtained. Anisops haemoglobin shows no Bohr effect, but appears to be very temperature-sensitive. During free dives the haemoglobin is regularly de-oxygenated ; the oxygen so derived probably helps to maintain the bug in neutral buoyancy for much of each dive. Carbon monoxide has been used to inactivate the haemoglobin, after which dives are reduced to about one-fifth of their normal duration and the phase of neutral buoyancy is abolished. Much of the oxygen which leaves the pigment probably diffuses into the ventral airstore and then re-enters the tracheal system via the thoracic spiracles. External ‘pumping’ movements may serve to speed this gas migration. It is argued that physical gill action plays a negligible part in the normal respiration of this species.