Journal
ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY
Volume 178, Issue 4, Pages 912-918Publisher
OXFORD UNIV PRESS
DOI: 10.1111/zoj.12502
Keywords
cryptobiosis; Ecdysozoa; extreme environments; ionic stress; osmobiosis
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Little is known about ionic and osmotic stress tolerance in tardigrades. Here, we examine salt stress tolerance in Ramazzottius oberhaeuseri and Echiniscus testudo from Niva (Denmark) and address whether limno-terrestrial tardigrades can enter a state of quiescence (osmobiosis) in the face of high external osmolyte concentrations. Direct transfers into NaCl solutions showed an upper tolerance level of around 600mOsmkg(-1) in R.oberhaeuseri and 200mOsmkg(-1) in E.testudo. During salt exposures, R.oberhaeuseri contracted into a tun', whereas E.testudo remained active leaving it more susceptible to acute effects of the ions. Further experiments focused on the more resilient R.oberhaeuseri, which entered a tun and readily regained activity when directly exposed to polyethylene glycol and sucrose of up to 872 +/- 0 and 813 +/- 3mOsmkg(-1), respectively, revealing a higher tolerance towards non-ionic osmolytes as compared to NaCl. Ramazzottius oberhaeuseri furthermore readily regained activity following gradual increases in non-ionic osmolytes and NaCl of up to 2434 +/- 28 and 1905 +/- 3mOsmkg(-1), respectively, showing that short-term acclimation promoted salt stress tolerance. Our results suggest that the limno-terrestrial R.oberhaeuseri enters a state of quiescence in the face of high external osmotic pressure and that it, in this state, is highly tolerant of ionic and osmotic stress.
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