Ramazzottius oberhaeuseri furthermore readily regained activity following gradual increases in non-ionic osmolytes and NaCl of up to 2434 ± ± 3 mOsm kg−1, respectively, showing that short-term acclimation promoted salt stress tolerance. Here, we examine salt stress tolerance in Ramazzottius oberhaeuseri and Echiniscus testudo from NivÃ¥ (Denmark) and address whether limno-terrestrial tardigrades can enter a state of quiescence (osmobiosis) in the face of high.-ionic osmolytes as compared to NaCl. Little is known about ionic and osmotic stress tolerance in tardigrades. Osmotic stress tolerance in semi-terrestrial tardigrades dujardini (and in other studied tardigrades compared to early stage embryos may partly be due to limited mitotic activity, since tardigrades have a low degree of somatic cell division (eutely, and dividing cells are known to be more sensitive to radiation. We suggest that the higher radiation tolerance in adults and late stage embryos of H. dujardini is a freshwater tardigrade with lower tolerance to desiccation compared to limno-terrestrial tardigrades, the high radiation tolerance in adults, similar to limno-terrestrial tardigrades, is unexpected and seems to challenge the idea that desiccation and radiation tolerance rely on the same molecular mechanisms. Finally we measured the effect of low temperature during irradiation at 4000 Gy and 4500 Gy on survival in adult tardigrades, and observed a slight delay in the expressed mortality when tardigrades were irradiated on ice. Juveniles hatched from eggs irradiated at 50 Gy and 200 Gy developed into adults and produced offspring, but their fertility was reduced compared to the controls. Survival of juveniles from irradiated eggs was highly affected by a 500 Gy dose, both in the early and the late stage. We also evaluated the effect of radiation (doses 50 Gy, 200 Gy, 500 Gy on eggs in the early and late embryonic stage of development, and observed a reduced hatchability in the early stage, while no effect was found in the late stage of development. In adults the LD50/48h for survival was estimated at ~ 4200 Gy, and doses higher than 100 Gy reduced both fertility and hatchability of laid eggs drastically. In this paper, we report studies on dose responses of adults and eggs of the tardigrade Hypsibius dujardini exposed to gamma radiation. Tolerance to Gamma Radiation in the Tardigrade Hypsibius dujardini from Embryo to Adult Correlate Inversely with Cellular Proliferation.įull Text Available Tardigrades are highly tolerant to desiccation and ionizing radiation but the mechanisms of this tolerance are not well understood. In addition, the evolutionary meaning of dormancy in tardigrades is discussed. The latter need a cue to hatch (dehydration followed by re-hydration. Our analysis of life history traits of a laboratory reared strain of a soil tardigrade revealed a particular hatching phenology that involved the production of both subitaneous and resting eggs. Several inter-specific differences have been identified, other than the production of two types of cysts in the semiterrestrial species. We analyzed more in detail encystment processes, comparing a semiterrestrial with a limnic species. Morphological changes during cyst formation are more complex than those involved in tun formation. Encystment involves at least the synthesis of new cuticular structures. As regards diapause, we considered encystment and eggs. We evaluated: i the long-term anhydrobiotic survival by comparing quantitative data on recovery from naturally induced desiccation in several species of tardigrades ii differences in survival patterns between species and populations by experimentally inducing anhydrobiosis and cryobiosis iii phenotypic factors affecting anhydrobiotic survival. Our research on cryptobiosis focused on some ecological and evolutionary aspects. Entering anhydrobiosis, tardigrades contract their body into a so-called tun, loosing most of their free and bound water (>95%, synthesizing cell protectants (e.g., trehalose, glycerol, heat shock proteins and strongly reducing or suspending their metabolism. Together with nematodes and bdelloid rotifers, tardigrades are known to enter quiescence (with several forms of cryptobiosis: anhydrobiosis, cryobiosis, anoxybiosis, osmobiosis at any stage of their life cycle, from egg to adult. Directory of Open Access Journals (Sweden)įull Text Available Tardigrades often colonise extreme habitats, in which they survive using both types of dormancy: quiescence and diapause.
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