Sensitivity of Metabolic Rate, Growth, and Fecundity of Tadpole Shrimp Triops longicaudatus to Environmental...

The influence of fluctuations of ambient oxygen tensions and temperature on the rate of oxygen consumption (VO2) was determined for the tadpole shrimp, Triops longicaudatus. VO2 was oxygen dependent up to 185 torr PO2, and Q10 for oxygen consumption between 20° and 30°C was 1.9. From these results it was estimated that oxygen consumption increases more than 1100 μl · g-1 · h-1 in T. longicaudatus for typical diurnal changes in temperature and oxygen in desert ephemeral pools. Elevated VO2 may be coupled with increased growth rate and fecundity, because these characteristics were highly sensitive to changes in ambient temperature and oxygen tension. Depressing mean daily temperatures by 2.3°C significantly decreased body mass, whereas hyperoxia (200 torr) significantly increased growth compared to that of animals raised under hypoxic conditions (70 torr). Fecundity was dependent on animal mass and ambient oxygen tension. Thus, for a 22-day season, one T. longicaudatus female could produce 30 more eggs per 10 torr increase in oxygen tension and 43 more eggs per 1°C change in mean daily temperature. These results indicate that there are selective pressures for metabolic sensitivity to the high temperature-high oxygen conditions of the ephemeral environments inhabited by T. longicaudatus.