RESPIRATORY ADAPTATIONS: INVERTEBRATES

Abstract

The major recent advances are: (1) increased precision in describing the relation of oxygen consumption to oxygen concentration, temperature, and activity; (2) recognition of cessation of oxygen consumption and survival of prolonged anoxia as common features of invertebrate respiration; and (3) integration of data on properties of enzymes and pathways of metabolism into the developing story of respiration with and without oxygen. Variation in rates of uptake with oxygen content of the medium can be described by a quadratic equation with three parameters chosen to express departure from strict conformity. Over certain segments of the environmental range, the oxygen uptake of some species increases with temperature only 1.2 to 1.4 times for 10°, rather than in accordance with the expected doubling of rate of chemical reactions. When animals survive very low oxygen tension for extended periods, they may be called “euryoxic”, a new term analogous to euryhaline and eurythermal. The term “facultative anaerobe” is inappropriate because all animals are aerobes. At least five species of bivalve mollusks are highly euryoxic, surviving 21 to 51 days of oxygen lack at low temperatures. Since rates of enzyme activity utlimately determine rates of oxygen uptake and acid production, the kinetic properties of enzymes, together with endogenous concentrations of substrates, activators, and inhibitors, must eventually predict respiration rates.