Enhanced drought tolerance of a soil-dwelling springtail by pre-acclimation to a mild drought stress

The springtail Folsomia candida has a highly permeable cuticle, but is able to survive several weeks at 98.2%RH. This corresponds to a water potential deficit of about 17 bars between the environment and the normal osmotic pr essure of the body fluids of this animal. Recent studies have shown a water vapour absorption mechanism by accumulation of sugars and polyols (SP) in F. candida, which explains how this species can survive dehydrating conditi ons. In the present study, adult F. candida were pre-acclimated at 98.2%RH to induce the accumulation of SP, and were subsequently exposed for additio nal desiccating conditions from 98 to 94%RH. Activity level, water content, osmotic pressure of body fluids and SP composition were investigated. Afte r the desiccation period, the animals were rehydrated at 100%RH and surviva l was assessed. The results showed that F. candida survived a more severe d rought stress when it had been pre-acclimated to 98.2%RH before exposure to lower humidity. This species was able to maintain hyperosmosity to the sur roundings at 95.5%RH, suggesting that it can absorb water vapour down to th is limit. Below this limit, trehalose levels increased while myo-inositol l evels decreased. We propose that this is a change of survival strategy wher e F. candida at mild desiccation levels seek to retain water by colligative means (remain hyperosmotic), but at severe desiccation levels switches to an anhydrobiotic strategy. (C) 2001 Elsevier Science Ltd. All rights reserv ed.