Water Flux and Metabolic Rates of Free-Roaming Scorpions Using the Doubly Labeled Water Technique

Abstract

Mean water loss rates for the desert scorpion Hadrurus arizonensis determined in the laboratory using doubly labeled water (tritium and oxygen-18) were significantly higher than mean rates determined gravimetrically for unfed animals. Differences between isotopically and gravimetrically determined water loss rates were not significant in steady-state animals or when the experimental periods were sufficiently long. Water turnover rates and water loss rates determined isotopically in freeroaming field scorpions were much higher than those for laboratory-confined individuals. Highest water loss values for free-roaming scorpions were observed following periods of rainfall which presumably increased food availability and, hence, water input. Mean metabolic rates of free-roaming scorpions were two to three times higher than rates determined under laboratory conditions at comparable temperatures. The application of the doubly labeled water technique to arthropods holds much promise but will require further refinement to ensure that data obtained are valid.