Oxygen uptake, critical oxygen tension, and available oxygen for three species of cave crayfishes

Oxygen consumption rates (MO2) were measured for 3 species of cave-dwelling crayfishes, Procambarus pallidus, Procambarus erythrops, and Troglocambarus maclanei. The MO2 values for the cave-dwelling species were compared to MO2 values measured previously over a broad range of masses in the surface-dwelling crayfish Pacifastacus leniusculus. MO2 values reported for other surface crayfish are not different from Pacifastacus leniusculus of the same mass. The MO2 values for the cave species were all significantly below the MO2 values for the surface crayfish of the same mass, indicating that the cave crayfish have reduced aerobic metabolism. Critical oxygen tensions or P(c)s (the ambient oxygen partial pressure (PO2) at which resting MO2 is no longer constant, but begins to decrease) measured for 2 of the cave species (P. pallidus, 29 Torr; T. maclanei, 25 Ton) were lower than those reported in the literature for surface species (35-40 Ton). The third cave species, P. erythrops, showed no decrease in MO2 down to an ambient PO2 of 20 Ton The PO2 measured in water samples taken from 6 of the same submerged caves in which the crayfish were found showed great variability (mean = 71 Torr; range = 26-145 Ton), but was not lower than the PO2 of surface water samples taken outside of the caves. This suggests that low oxygen availability may not have been the primary selective force in the evolution of reduced oxygen uptake rates in cave crayfish.