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

NASA Ames Research Center, Moffett Field, California, USA.
Astrobiology (Impact Factor: 2.51). 04/2012; 12(4):283-9. DOI: 10.1089/ast.2011.0669
Source: PubMed

ABSTRACT 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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    • "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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