Comparative water relations of four species of scorpions in Israel: evidence for phylogenetic differences

In an attempt to determine the nature of possible interspecific differences in osmotic responses to dehydration, the following species of two scorpion families were examined: Scorpio maurus fuscus (Scorpionidae) and Buthotus judaicus (Buthidae) from the mesic Lower Galilee (mean annual precipitation approximately 525 mm); and Scorpio maurus palmatus (Scorpionidae) and Leiurus quinquestriatus (Buthidae) from the xeric Negev Desert (mean annual precipitation approximately 100 mm). When sampled in the laboratory following their capture, B. judaicus (548+/-38 mOsm l(-1); mean +/- S.D.) and L. quinquestriatus (571+/-39 mOsm l(-1)) had higher and less variable haemolymph osmolarities than the scorpionids occupying the same habitats (511+/-56 and 493+/-53 mOsm l(-1) for S. m. fuscus and S. m. palmatus, respectively). In response to 10% mass loss when desiccated at 30 degrees C, the haemolymph osmolarity of the two buthids increased by 5-9%, compared to ca. 23% in the two scorpionids. Buthids had lower water loss rates than scorpionids. The similar oxygen consumption rates, when converted to metabolic water production, imply a higher relative contribution of metabolic water to the overall water budget of buthids. This could explain why the osmoregulative capabilities exhibited by buthids are better than those of scorpionids. We conclude that the observed interspecific differences in water and solute budgets are primarily phylogenetically derived, rather than an adaptation of the scorpions to environmental conditions in their natural habitat.