Tolerance of Anhydrobiotic Eggs of the Tardigrade Ramazzottius varieornatus to Extreme Environments

NASA Ames Research Center, Moffett Field, California, USA.
Astrobiology (Impact Factor: 2.59). 04/2012; 12(4):283-9. DOI: 10.1089/ast.2011.0669
Source: PubMed


Tardigrades are tiny (less than 1 mm in length) invertebrate animals that have the potential to survive travel to other planets because of their tolerance to extreme environmental conditions by means of a dry ametabolic state called anhydrobiosis. While the tolerance of adult tardigrades to extreme environments has been reported, there are few reports on the tolerance of their eggs. We examined the ability of hydrated and anhydrobiotic eggs of the tardigrade Ramazzottius varieornatus to hatch after exposure to ionizing irradiation (helium ions), extremely low and high temperatures, and high vacuum. We previously reported that there was a similar pattern of tolerance against ionizing radiation between hydrated and anhydrobiotic adults. In contrast, anhydrobiotic eggs (50% lethal dose; 1690 Gy) were substantially more radioresistant than hydrated ones (50% lethal dose; 509 Gy). Anhydrobiotic eggs also have a broader temperature resistance compared with hydrated ones. Over 70% of the anhydrobiotic eggs treated at either -196°C or +50°C hatched successfully, but all the hydrated eggs failed to hatch. After exposure to high-vacuum conditions (5.3×10(-4) Pa to 6.2×10(-5) Pa), the hatchability of the anhydrobiotic eggs was comparable to that of untreated control eggs.

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Available from: Lynn Rothschild, Dec 14, 2014
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    • "However, a recent study evaluated the tolerance of Ramazzottius varieornatus eggs to alpha particles (4H). Both hydrated and anhydrobiotic eggs were affected by radiation, but hydrated eggs were considerably more sensitive [15]. Exposure of tardigrade eggs (Milnesium tardigradum, Richtersius coronifer) to space conditions (UV and cosmic radiation, vacuum) led to complete mortality, but when eggs were sheltered from UV radiation, hatchability was not affected [16]. "
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    ABSTRACT: Tardigrades represent one of the most desiccation and radiation tolerant animals on Earth, and several studies have documented their tolerance in the adult stage. Studies on tolerance during embryological stages are rare, but differential effects of desiccation and freezing on different developmental stages have been reported, as well as dose-dependent effect of gamma irradiation on tardigrade embryos. Here, we report a study evaluating the tolerance of eggs from the eutardigrade Milnesium cf. tardigradum to three doses of gamma radiation (50, 200 and 500 Gy) at the early, middle, and late stage of development. We found that embryos of the middle and late developmental stages were tolerant to all doses, while eggs in the early developmental stage were tolerant only to a dose of 50 Gy, and showed a declining survival with higher dose. We also observed a delay in development of irradiated eggs, suggesting that periods of DNA repair might have taken place after irradiation induced damage. The delay was independent of dose for eggs irradiated in the middle and late stage, possibly indicating a fixed developmental schedule for repair after induced damage. These results show that the tolerance to radiation in tardigrade eggs changes in the course of their development. The mechanisms behind this pattern are unknown, but may relate to changes in mitotic activities over the embryogenesis and/or to activation of response mechanisms to damaged DNA in the course of development.
    Full-text · Article · Sep 2013 · PLoS ONE
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    • "However, the initial decline was not as steep as in the current study, and hatchability of control eggs was also higher (100%). Horikawa et al. (2012) reported an LD 50 value for hydrated eggs of 509 Gy based on a linear regression , considerably higher than our estimate of 48 Gy, but due to several differences in methodology and use of different kinds of radiation (alpha vs gamma) these estimates are not directly comparable. A few other studies have evaluated tolerance of tardigrade eggs to radiation, without examining responses to dose. "
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