Eight species of eutardigrades collected in different terrestrial and freshwater habitats and characterized by different anhydrobiotic capabilities have been submitted to freezing and thawing experiments. The aim was to test: i. the interspecific capability to survive cryobiosis and the differences in recovery time to active life; ii. the relationship between survival and cooling rates. Starting from a uniform condition of tardigrades maintained for 24 h in water at 14°C, the cooling was performed according to three different protocols. Experiment 1: replicates for each species considered were put in 4 ml of water, frozen at three temperatures (-9°C, -20°C and -80°C) and kept frozen for six days. Experiment 2: replicates of Ramazzottius oberhaeuseri and Amphibolus volubilis were put in 4 ml of water, frozen in liquid nitrogen for two minutes and then stored at –9°C. Experiment 3: replicates of R. oberhaeuseri were placed in different amounts of water (2 ml, 1 ml and 0.5 ml), frozen at three different temperatures as in experiment 1 and kept frozen for six days. Before thawing, all frozen animals were firstly put or maintained at –9°C and then thawed at 14°C. Animals were examined both after 2.5 h and 24 h, considering alive the animals with evident and coordinated body movements. In experiment 1, R. oberhaeuseri, A. volubilis, Macrobiotus areolatus and Macrobiotus richtersi show a high survival at any tested temperature. Hypsibius dujardini, Borealibius zetlandicus and Diphascon cf. scoticum show a lower survival and differences in survival among each temperature. Survival of Dactylobiotus parthenogeneticus is null at any tested temperature. In most cases, the recovery time increases with the fall of the temperature and differs among the species. The differences among the species seem clearly related to the habitat and above all to the capability to carry out anhydrobiosis, suggesting a strong relationship between anhydrobiosis and cryobiosis. In experiment 2, all specimens of both species did not survive to freezing at –196°C. In experiment 3, R. oberhaeuseri shows high survival also when the animals are frozen in less than 4 ml of water, even though a survival decrease is recorded between –9°C and –80°C for all tested water amounts. In general, the survival is lower when the water freezing time is shorter (corresponding to a higher cooling rate). Moreover, a negative relationship between the water freezing time and the recovery time has been found: the shorter the water freezing time, the longer the recovery time. A too short water freezing time does not allow survival. These results can be easily explained by the need to produce a sufficient amount of protectants, or not enduring too many damages.
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|Data di pubblicazione:||2006|
|Autori:||R. Bertolani; L. Rebecchi; D. Boschini; R. Guidetti|
|Titolo:||Cryobiosis survival in tardigrades.|
|Appare nelle tipologie:||Abstract in Atti di Convegno|
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