Abstract
It has recently been argued that the enigmatic tardigrades (water bears) will endure until the sun dies, surviving any astrophysical calamities in Earth’s oceans. Yet, our knowledge of stress tolerance among marine tardigrade species is very limited and most investigations revolve around species living in moist habitats on land. Here, we investigate desiccation tolerance in the cosmopolitan marine tidal tardigrade, Echiniscoides sigismundi, providing the first thorough analysis on recovery upon desiccation from seawater. We test the influence on survival of desiccation surface, time spent desiccated (up to 1 year) and initial water volume. We propose analysis methods for survival estimates, which can be used as a future platform for evaluating and analysing recovery rates in organisms subjected to extreme stress. Our data reveal that marine tidal tardigrades tolerate extremely rapid and extended periods of desiccation from seawater supporting the argument that these animals are among the toughest organisms on Earth.
Highlights
It has recently been argued that the enigmatic tardigrades will endure until the sun dies, surviving any astrophysical calamities in Earth’s oceans
Anhydrobiosis refers to cryptobiosis induced by desiccation, cryobiosis to cryptobiosis induced by freezing, and osmobiosis to cryptobiosis induced by elevated external osmotic pressure
Previous studies on desiccation tolerance have focused on various invertebrates, including nematodes, rotifers and the brine shrimp, Artemia salina[30,31,32]
Summary
Survival of Echiniscoides sigismundi preserved in a hydrated and starved condition. Control groups were kept hydrated in sterile filtered seawater without substrate for up to 6 weeks (Table 1, Fig. 2). We found that there was a statistically significant effect of both the desiccation surface (χ 2(2) = 468.08, p < 0.01) and the desiccation time (χ2(2) = 225.93, p < 0.01) on the survival rate of specimens desiccated for up to 48 hours, with specimens desiccated on filter paper having a significantly greater chance of survival than specimens desiccated on glass or hedgehog spines (Fig. 3). Based on the data of the filter paper desiccated tardigrades we estimated a log-logistic model of survival rate, with time spent desiccated (taken as a continuous variable) as the single explanatory variable.
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