18 June, 2009

Water loss in scorpions living in arid environments

Scorpions are very common in many arid areas and many species are well adapted to a life in areas with high temperatures and low precipitation. One of the main adaptions to life in such harsh environments is to reduce loss of body water. Body water is lost to the environment mainly through the skin (cuticular water loss) and through respiration (respiratory water loss). In scorpions, the main loss of body water is through the respiration.

A recent study by Gefen, Ung & Gibbs (2009) looks into water loss in the North American species Hadrurus arizonensis (Caraboctonidae). See abstract for details about the study and its results.

Terrestrial arthropods lose body water to the environment mainly through transpiration. The aim of this study was to determine the fraction of respiratory losses from total transpiratory water loss in scorpions, as relatively high respiratory losses would indicate a fitness benefit from regulation of gas-exchange rate under stressful desiccating conditions. We measured metabolic rates and water-loss rates of Hadrurus arizonensis (Iuridae) at a range of ecologically-relevant temperatures. Calculation of respiratory water losses was based on increased metabolic and water-loss rates during nocturnal activity (assuming no change in cuticular resistance at a given constant experimental temperature). Respiratory losses accounted for 9.0 ± 1.7% of total transpiratory losses at 25 °C, doubled to 17.9 ± 1.8% at 30 °C and increased to 31.0 ± 2.0% at 35 °C (n = 5, 15 and 15, respectively). Furthermore, the relative importance of respiratory transpiration is likely to be higher at temperatures above 35 °C, which have been recorded even within the burrows of H. arizonensis. Measurements of cuticular lipid melting points do not provide evidence for increased cuticular resistance to water loss at higher temperatures. However, the relatively high fraction of respiratory water losses reported here for H. arizonensis supports the notion of respiratory regulation as an evolved mechanism for conserving scorpion body water stores under stressful conditions.

Gefen E, Ung C, Gibbs AG. Partitioning of transpiratory water loss of the desert scorpion, Hadrurus arizonensis (Iuridae). J Insect Physiol. 2009 Jun;55 (6):544-8. [Subscription required for fulltext]

Family Caraboctonidae

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