Discontinuous gas exchange in a tracheate arthropod, the pseudoscorpion Garypus californicus: Occurrence, characteristics and temperature dependence.

The discontinuous gas exchange cycle of the pseudoscorpion Garypus californicus, mean mass 5.9 mg, is rudimentary and is characterized by bursts of CO(2) at frequencies ranging from 3.6 mHz at 15°C to 13.3 mHz at 35°C. The mean volume of CO(2) emitted per burst is 3.6 µl g(−1) at 25°C, about a tenth of the amount emitted by tracheate arthropods with a well developed discontinuous gas exchange cycle. Interburst CO(2) emission is high and increases with temperature, reaching near 45% of total CO(2) production rate at 35°C. No fluttering spiracle phase is evident. The metabolic rate of G. californicus at 25°C (8.4 µW) is typical of other arthropods. We infer from the high rate of interburst CO(2) emission in G. californicus that trans-spiracular O(2) partial pressure gradients are small and that spiracular conductance is correspondingly high, which may lead to high rates of respiratory water loss relative to arthropods with more stringent spiracular control and higher CO(2) buffering capacity. The typical moist, hypogeal environments and small body sizes of pseudoscorpions correlate well with their respiratory physiology.