Harper, S.L.; Reiber, C.L.: Deviants of gas exchange: adaptations of the tadpole shrimp

Tadpole shrimp Triops longicaudatus inhabiting a rock pool in southern Nevada experience prolonged hypoxia. Diel oxygen concentrations (Po₂) in the pool range from 0-20 kPa O₂. Tadpole shrimp were reared under low (1-3 kPa) and high (10-13 kPa) Po₂‘s to determine the influence of rearing Po₂ on adult responses to hypoxic stress and to determine the regulatory mechanisms employed by tadpole shrimp to deal with both chronic and acute hypoxia. Respiratory surface area is significantly decreased in animals reared under chronic hypoxia. This decrease is presumably due to limited oxygen available to fuel metabolic anabolism and formation of larger respiratory appendages. Accessory respiratory surfaces, such as the hindgut, aid in the diffusion of oxygen into the animal regardless of their rearing environment but appear to primarily assist smaller anaimals in extracting supplemental oxygen. This is ecologically important because smaller tadpole shrimp cannot regulate oxygen uptake as readily as larger, more mature animals. Ventialtory rates and volumes do not change with varying oxygen tensions, however, oxygen extraction increases significantly under low oxygen concentrations in both field and experimental animals. Tadpole shrimp from the rock pool in Brownstone Canyon appear to be highly adapted to the low oxygen concentrations prevalent in the pool.