NASA Ames Research Center, Moffett Field, California, USA.
Astrobiology. 2012 Apr;12(4):283-9. doi: 10.1089/ast.2011.0669. Epub 2012 Apr 10.
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.
缓步动物是微小的（长度小于 1 毫米）无脊椎动物，由于其通过称为干燥非新陈代谢状态的方式对极端环境条件具有耐受性，因此有可能能够前往其他行星生存。虽然已经报道了成年缓步动物对极端环境的耐受性，但关于其卵的耐受性的报道很少。我们研究了 Ramazzottius varieornatus 缓步动物的水合和无水生物卵在暴露于电离辐射（氦离子）、极低和高温以及高真空下孵化的能力。我们之前报道过水合和无水生物成年个体对电离辐射的耐受性存在相似的模式。相比之下，无水生物卵（50%致死剂量；1690 Gy）的辐射抗性明显强于水合卵（50%致死剂量；509 Gy）。无水生物卵的温度耐受性也比水合卵宽。在 -196°C 或 +50°C 处理的无水生物卵中，超过 70%成功孵化，但所有水合卵都未能孵化。在暴露于高真空条件（5.3×10(-4) Pa 至 6.2×10(-5) Pa）后，无水生物卵的孵化能力与未经处理的对照卵相当。
