Thermotolerance at three temperatures of high Andean limnic tardigrades
Tardigrades, a phylum of microscopic organisms well known for their resistance to extreme conditions thanks to adaptations such as cryptobiosis, in which they are able to suspend their metabolism until more favorable conditions arise. These organisms are found in a wide range of environments, and high Andean mountains are not the exception, even though weather conditions are highly variable during the day, let alone a month. An experiment was thus conducted in Bogotá, Colombia at the campus of the National University of Colombia to evaluate the resistance of limnic tardigrades found on trees, three sets of fifteen tardigrades were exposed to 20°C, 30°C and 40°C , at a rate of 0,5°C/min, which were then examined to determine the number of alive, dead or in “tun” organisms. The results for the tardigrades exposed at 20°C were 4 dead in the first set and 3 dead in the second and third set; at 30°C, 6 dead in the first set and 5 dead in the second and third set; at 40°C, 6 dead in the first set, 7 dead in the second set and 8 dead in the third set. Succinctly, 22,22% were dead at 20°C; 35,56% were dead at 30°C and 46,67% were dead at 40°C. No tardigrades were found in “tun” state at any temperature. Therefore, the data shows an increase in mortality as the temperature rises, even so, taking into account the climatic conditions registered, studied tardigrades are able to withstand higher temperatures than what they are exposed to usually, moreover Andean tardigrades do not show phenotypic plasticity or adaptation. As for the lack of “tun” state it implies that high temperatures, at least at this rate, do not trigger this state while conditions like desiccation do, more research is needed on this account.
Steps to reproduce
Tardigrades used for this study were extracted from different moss samples taken from trees on the Bogotá campus of Universidad Nacional de Colombia (4°38'30.61875" N and 74°4'57.06839" W). Samples were taken with tweezers and placed upside down with mineral water in petri dishes, after 2-3 hours of hydration the moss was removed and the petri dish placed under the stereoscope, tardigrades were then searched throughout the dish. Once found, using a micropipette the tardigrade was extracted and placed in individual Eppendorfs with 0,5 mL mineral water. Each set of 15 was then placed on a heating plate and heated to 30°C at a rate of 0,5°C/min. Eppendorfs were then left to cool down and examined a few hours later, each treatment was repeated 3 times at 20°, 30°and 40°. Since 135 tardigrades were needed for the study, the moss samples were kept in the lab, as to not harm moss growth furthermore in the environment; each petri dish remained closed and had cotton swabs with water in order to maintain humidity at >90% inside, moss temperature was on average 18°C. A HOBO® Pro v2 (U23-004) data logger with sensors for both ambient and substrate temperature was used to determine weather conditions. It was left for 29 days from October 18th to November 16th of 2023.