Reference: Vecchi, M., Adakpo, L. K., Dunn, R. R., Nichols, L. M., Penick, C. A., Sanders, N. J., Rebecchi, L., & Guidetti, R. (2021). The toughest animals of the Earth versus global warming: Effects of long-term experimental warming on tardigrade community structure of a temperate deciduous forest. Ecology and Evolution, 11, 9856-9863. https://doi.org/10.1002/ece3.7816
Who Can Take the Heat?
It is no secret that climate change is causing rapid and catastrophic changes to environments across the world. Climate change experts predict global temperatures will rise 2.5 to 10 degrees Fahrenheit in the next 100 years. While some living things can adapt to these rapidly changing conditions, many will die off due to habitat loss among many other potential reasons. Consequently, essential ecosystems will no longer function with the loss of crucial members. For example, climate change is forcing algae from their coral hosts in coral reefs. Without these algae, the coral cannot survive causing the decline of coral reefs that are essential for maintaining biological diversity.
Researchers hope to beat the grim odds by understanding how climate change will affect organisms. Their goal is to figure out how we can protect organisms and their ecosystems from impending doom. One way to determine how we can preserve vulnerable species is to understand how some organisms survive such harsh conditions. The wild has shaped many tough animals, from venomous snakes to fierce bears, but the experts have turned to the toughest animal on Earth to see if they can take the heat. Although it is commonly called a (water) bear, none are tougher than the microscopic, soil-dwelling tardigrade.
Small, but Fierce
Tardigrades are tiny (usually less than a millimeter) aquatic animals. However, their microscopic size makes even a drop of water suitable habitat. Tardigrades can call nearly every habitat home, from the bottom of the ocean to the icy Antarctic. Tardigrades survive temperatures as low as -328 oF and as high as 304 oF. Lethal doses of radiation, boiling alcohol, and toxic chemicals are no bother to the water bear. They can also survive up to 30 years without oxygen and water! To achieve such feats, tardigrades enter a death-like state by stopping many internal processes that maintain life.
Tardigrades are tough, but are they tough enough to survive climate change? Water bear researchers, like Matteo Vecchi, were determined to find the answer. In Duke Forest, North Carolina, the researchers set up 12 plots with heating chambers that warm the leaf litter and soil. Based on climate change predictions, the chambers ranged from a 2.5 oF to 10 oF temperature increase from the current temperature. After five years, the researchers collected two leaf litter samples from each plot to count and identify the number of tardigrades.
Not surprisingly, they found that rising temperature did not affect the types of tardigrades or their numbers in the leaf samples. There was, however, variation in tardigrade abundance between samples at the same plot. This variation could suggest that suitable conditions for tardigrades are patchy in the leaf litter.
The Tough Survive. Will the Rest?
High temperatures – even those predicted as a worst-case scenario by the Intergovernmental Panel on Climate Change (an increase of 10 oF) – are no match for the tardigrades of North Carolina. There are several reasons why tardigrades may be equipped to survive such harsh conditions. First, tardigrades may do just fine, or even prefer, warmer conditions. Scientists often find that animals that prefer higher temperatures can handle extreme temperature changes due to climate change. Second, the tardigrades could enter the death-like state called cryptobiosis, allowing them to survive severe conditions with ease. This behavior may not be sustainable if temperatures never lower, as tardigrades cannot reproduce while in this state. Last, the leaf litter provides patchy conditions which supply a variety of microhabitats to support tardigrades. For example, leaf litter closer to the ground or in the shade may be cooler and wetter than leaves on top or in the sun. More vulnerable animals may be able to use patchy habitats to choose favorable spots as temperatures rise.
Knowing that the toughest animals alive can survive climate change is good news, but scientists have found many animals will not be so lucky. Particularly little is known about the effect of climate change on microscopic, soil-dwelling animals, many of which are essential for decomposition and nutrient cycling. With the consequences of climate change looming, experts must determine how it will impact animals and how we can protect them before it is too late. By understanding how the toughest animal survives the harsh conditions, we can start to figure out how to protect those more vulnerable.