GEFEN, E.; Univ. of Nevada, Las Vegas: Interspecific differences in water relations of scorpions: a new perspective
Scorpions are thought to follow the water permeability:habitat relationship. Similarly, while scorpions are generally considered as poor osmoregulators the osmoregulatory capacities of the xeric buthid Parabuthus villosus were viewed as a useful adaptation to its xeric distribution. However, all Old World xeric species included in comparative water relations studies have belonged to the Buthidae family and compared to species of other families. In order to determine the nature of possible interspecific differences in osmotic responses to desiccation, the following scorpion species were examined: the mesic Scorpio maurus fuscus (Scorpionidae) and Buthotus judaicus (Buthidae) and xeric Scorpio maurus palmatus (Scorpionidae) and Leiurus quinquestriatus (Buthidae). Following capture, B. judaicus (548±38mOsm/l; mean±S.D.) and L. quinquestriatus (575±39mOsm/l) had higher and less variable haemolymph osmolarities than sympatric scorpionids (511±56 and 487±53mOsm/l for S. m. fuscus and S. m. palmatus respectively). After two weeks of ad lib feeding, the scorpions were desiccated at 30oC and 40-60% relative humidity. Following a 10% mass loss, the haemolymph osmolarity of B. judaicus increased by 5% whereas that of L. quinquestriatus increased by 9%. In comparison, the two scorpionids showed a significantly higher increase of 23% in haemolymph osmolarity following the same mass loss. The lower water loss rates of both buthids are reflected in their better osmoregulatory capabilities, largely as a result of the enhanced compensatory role of metabolic water production in species of this family. These characteristics may provide an adaptation to surface-dwelling existence, as unlike most other scorpion species buthids rarely burrow, and are thus more exposed to climatic extremes.
