Investigating the Osmotic Stress Tolerance of the Tardigrade Hypsibius exemplaris

Abstract:

While the use of tardigrades as a model system for the study of extreme environments continues to increase, there is still much to be learned about the mechanisms these resilient animals use to tolerate such harsh conditions. As a result, the development of an accessible model system for the study of tardigrade survival and recovery after exposure to inhospitable conditions is paramount to elucidating these mechanisms. Osmotic stress was chosen as the environmental condition of interest for this project due to the wide availability of sodium chloride (NaCl) and the small amount of literature published on this specific topic. Individuals of the tardigrade species Hypsibius exemplaris were exposed to different concentrations of aqueous NaCl for 24 hours to induce osmotic stress, after which they were returned to deionized water and monitored for the next 48 hours to observe activity (measurement of survival and recovery). Tardigrade activity at the concentrations 200, 400, and 600 mOsm/kg was extremely rare, while activity at 50 mOsm/kg was indistinguishable from the control (deionized water). Although these results conflicted with published literature detailing the ability of H. exemplaris to withstand extreme conditions, further inquiry revealed that H. exemplaris has primarily been documented to survive harsh conditions after a period of acclimation. As a result, further experiments will be conducted with a period of acclimation to determine the maximum NaCl concentration that H. exemplaris can tolerate and subsequently recover from. Establishing the upper limit to the NaCl tolerance of this widely accessible species will allow for reproducible experiments that could investigate DNA/RNA/protein expression at different stages of cryptobiosis, physiological changes that may occur after exposure to osmotic stress, and countless other novel research questions that can contribute to the future study of adaptations extreme conditions.