PULLMAN – Earth’s most heat-tolerant animals may not live in the tropics or a desert. They likely live at the bottom of the ocean, around hydrothermal vents where magma seeps out of the planet’s interior. Near the vents, molten minerals mix with frigid seawater to create habitats that are home to some of the oddest – and hardiest – organisms known.
Among the most abundant members of the vent community are tube worms, distant relatives of earthworms, which cluster densely around the vents in water that often reaches scalding temperatures.
Washington State University biologist Raymond Lee, in collaboration with Peter Girguis of Harvard University, has found that tube worms of the species Paralvinella sulfincola thrive at temperatures of 40 to 50 degrees Celsius (104 to 122 degrees Fahrenheit). This is the highest temperature shown to be tolerated by aquatic multicellular animals, and the first direct measurement of thermal tolerance and preference in tube worms from hydrothermal vents.
“As evolutionary physiologists, we’re interested in all the different ways that animals have engineered to cope with their environment,” said Lee.
“Extreme organisms like these have pushed the limits” of what’s possible, he said.
Their results are published in the April 14 issue of the journal Science.
Lee is an associate professor in WSU’s School of Biological Sciences.
Girguis and Lee further found that the worms die with two hours of exposure to 55 C (131 F) or a few minutes of exposure to 60 C (140 F). Those findings were significant because tube worms of a related species, Alvinella pompejana, had previously been reported to live at 60 C (140 F) and to tolerate brief exposure to 80 C (176 F). Lee said he and many other scientists were skeptical of that report, because most of the enzymes and other proteins critical to life stop functioning normally at temperatures between 45 and 55 degrees Celsius.
The earlier measurements, obtained by researchers at the University of Delaware, were based on readings from a remote-controlled thermometer thought to be inserted into the shell-like covering of a tube worm at a hydrothermal vent. By contrast, Lee and Girguis brought tube worms into the lab, where their temperature could be controlled and their behavior continuously monitored.
Lee placed the worms in a chamber of his own design that held the worms at the high pressure characteristic of their native habitat, while allowing him to film the animals over several hours. Heating and cooling elements created a temperature gradient within the chamber. The worms were free to seek their preferred temperature.
“I consider this to be a big step in resolving this issue. For one of these to live at 60 degrees is very unlikely.”
The worms are members of the alvinellid family, which was named for the deep-sea research submarine Alvin. Hydrothermal vents were first discovered in the 1970s by scientists aboard the Alvin.
Lee’s research has implications for understanding how animals cope with environmental stresses and how the physical environment affects distribution of species. It also provides clues to how life first arose on Earth, and what forms of life might exist on other planets or their moons.
Although generally regarded as an “extreme” environment, the deep ocean actually represents about 90 percent of the habitable space on Earth, said Lee. And because conditions at hydrothermal vents are thought to resemble the conditions that once prevailed over much of the planet, Lee said the organisms living near vents offer a glimpse at the origins of life on Earth.
“The animals there aren’t from the beginning of Earth, but others like them existed before any others. The vents may represent the system where life first evolved.”
He also said solving the practical problems of studying vent animals, either in their natural habitat or in special chambers in the lab, lays the groundwork for the techniques that will be needed to study organisms from other worlds.
“Vent organisms may be as difficult to deal with as something from another planet,” he said. “It’s all remotely operated. If we find something on Mars it will be the same situation, just a longer distance.”
For a ”time-lapse” video of tubeworms try:
https://www.wsu.edu/~rlee/sulfideworm/psulf.html
For photos of tubeworms try the University of Deleware:
https://www.ocean.udel.edu/extreme2003/creatures/tubeworms/index.html
