Water loss in scorpions

Scorpions are known for low metabolic rates and low water loss rates. Previously, we have learned that mesic and/or burrowing species have had lower water loss rates than xeric species due to a life in a "better" microclimate. A new study shows that it ain't necessarily so.

Eran Gefen have now published a very interesting study investigating how the relative importance of respiratory water loss is correlated with species habitat type and activity pattern, using both xeric and mesic and burrowing and non-burrowing species. Also, Gefen's study has an improved experimental design placing the scorpions in a more realistic situation during experiments and thereby getting more realistic data for water loss and metabolic rates.

A summery of the results and conclusions can be seen in the abstract below.

Abstract:
Scorpions exhibit some of the lowest recorded water loss rates compared with those of other terrestrial arthropods of similar body size. Evaporative water loss (EWL) includes cuticular transpiration and respiratory water loss (RWL) from gas exchange surfaces, that is, book lung lamellae. Estimated fractions of cuticular and respiratory losses currently available from the literature show considerable variation, at least partly as a result of differences in methodology. This study reports RWL rates and their relative importance in scorpions from two families (Buthidae and Scorpionidae), including both xeric and mesic species (or subspecies). Two of the included Buthidae were surface-dwelling species, and another inhabits empty burrows of other terrestrial arthropods. This experimental design enabled correlating RWL importance with scorpion phylogeny, habitat type, and/or homing behavior. Buthidae species exhibited significantly lower EWL rates compared with those of Scorpionidae, whereas effects of habitat type and homing behavior were not significant. Resting RWL rates were not significantly affected by scorpion phylogeny, but rates for the xeric species (totaling ∼10% of EWL rates at 30 C) were significantly lower compared with those of mesic species. These lower RWL values
were correlated with significantly lowerH2O/CO2 emission rates in xeric species. The experimental setup and ∼24-h duration of each individual recording allowed estimating the effect of interspecific variation in activity on RWL proportions. The high respiratory losses in active hydrated Scorpio maurus fuscus, totaling 30% of EWL, suggest that behavioral discretion in this species is a more likely mechanism for body water conservation under stressful conditions when compared with the responses of other studied species.

Reference:
Gefen E. The Relative Importance of Respiratory Water Loss in Scorpions Is Correlated with Species Habitat Type and Activity Pattern. Physiol Biochem Zool. 2010 Nov 19. [Published ahead of print] [Subscription required for fulltext]

Thanks to Dr. Gefen for sending me this paper!