Respiratory concerts revealed by scanning microrespirography in a termite Prorhinotermes simplex (Isoptera: Rhinotermitidae)

Abstract

Respiratory metabolism of different developmental stages (larvae, pseudergates, nymphs, soldiers, neotenic reproductives; 0.6–4.5 mg body mass) of Prorhinotermes simplex was individually monitored by scanning respirographic method sensitive to subnanoliter amounts of O 2 consumption or CO 2 output per minute. Specimens exposed to dry air after removal from the colony performed enormously large, discontinuous bursts of CO 2 lasting usually 2 min. The volume of CO 2 produced during the burst often surpassed the volume of the whole body and it was 10- to 20-fold in excess of the air-filled endogenous tracheal volume. The initial velocity of CO 2 production during the burst was more than 90-fold faster in comparison to O 2 consumption. In the presence of enough moisture within the respiratory vessel, the termites breathed continuously without any larger outburst of CO 2. This fact fully corroborates validity of the so-called water retention theory in discontinuous CO 2 release. The highest rates of O 2 consumption were found in the second instar larvae (0.9 mg, 1000–2000 μl O 2/g/h), the soldier caste was intermediate (700 μl O 2/g/h) while pseudergates and neotenic reproductives consumed between 300 and 600 μl O 2/g/h, at 25 °C. All developmental stages feeding on a cellulose diet had CO 2/O 2 values (RQ) over 1 (1.2–1.4, i.e. carbohydrate metabolism), pigmented soldiers fed by the workers had RQ around 0.75 (predominating lipid or protein metabolism). The unusually large, sudden eruptions of CO 2 in specimens exposed to dry air allow us to make the following conclusions: (1) the bursts were due to special chemical processes, such as by enzymatic hydration of carbonic acid by carbonic anhydrase and; (2) the bulk of chemically evolved gaseous CO 2 escaped from the body by a mass flow supported by active ventilation, not by a passive diffusion. These results demonstrated that the periodic emissions of CO 2 and the associated homeostatic regulation of the respiratory acidaemia were under perfect physiological control. The termites could thus actively select the type of CO 2 release best suited to the extant environmental or internal physiological conditions, i.e. from a completely continuous respiration to occasionally cyclic or completely discontinuous CO 2 release.