Temperature and starvation affect the hemolymph acid-base balance of the xeric yellow scorpion,Leiurus quinquestriatus

Summary Water conservation is crucial for terrestrial animals such as scorpions which generally live in xeric habitats. One route of water loss is evaporation from their book lungs. In order to save water, scorpions may have a high resistance to gas exchange with the environment. If this is so then the partial pressure of CO₂ in their hemolymph, PCO₂, must be high. Does this affect their acid-base balance? Hemolymph PCO₂ and pH in normally-fed or starved desert-dwelling yellow scorpions Leiurus quinquestriatus were studied in vivo as functions of temperature. An ambient temperature increase (lasting at least 3 days) resulted in a rise of PCO₂ and a fall of pH, with thermal coefficients of 1.6 Torr · °C^-1 and-0.016 pH unit · °C^-1, respectively. The thermal coefficients for cell-free hemolymph studied in vitro were the same. At 28 °C, 3–6 weeks of starvation led to a 4.8 Torr increase in PCO₂ and a 0.056 unit decrease in pH. The in vivo PCO₂ values are among the highest, and pH values are the lowest of the terrestrial arthropods studied so far, e.g., at 28 °C they are 29 Torr and 7.15 pH respectively. It is argued that this particular acid-base balance with a marked hypercapnia is typical of a successful xeric air-breathing animal.Abbreviations ABB acid-base balance - PCO₂ partial pressure of CO₂ - PO₂ partial pressure of O₂