Sneezing is far from a behavior unique to humans. Maybe you’ve seen your dog or cat do this, or watched a YouTube video of a giraffe sneezing at an unsuspecting toddler at the zoo. The fact that sneezing doesn’t even require a nervous system, let alone a nose, goes back to some of the earliest multicellular animals: sponges.
Sponges have been around for at least 600 million years. “It’s the most successful animal I know of because it’s so ancient and ubiquitous,” says Jasper de Goeij, a marine ecologist at the University of Amsterdam. As filter feeders, sponges play a vital role in their aquatic ecosystems, absorbing water laden with a variety of organic matter, processing it and releasing it as waste, and organisms such as snails, sea snakes, and tubeworms use them to for food. “A sponge is basically an animal with a lot of small mouths and one or a few larger outflow openings,” says Dr de Goeij. Those “little mouths” are called ostia, and the openings through which water flows are called oscula.
Scientists have known for years that sponges can regulate water flow through minute-long body contractions — known as “sneezes” — but now, Dr. de Goeij and his colleagues have found that sponges appear to sneeze. Self-cleaning, releasing waste particles from mucus through openings. The work was published Wednesday in Current Biology.
Researchers stumbled upon the sneezing sponge while working on a project to study the role sponges play in moving nutrients through coral reef ecosystems. The work required Niklas Kornd, another marine ecologist in Amsterdam, to spend a lot of time studying sponges. “I would spend all day looking at their surfaces; it was boring,” he recalls. (At the time, Mr. Coender was scuba diving in the Caribbean.)
Fortunately, things got more interesting when he started seeing opaque filaments emerging from the sponge. “Then I’ll come back later and the goo is gone,” he said.
To figure out what those “sticky things” might be, the researchers recorded time-lapse footage of sponges, specifically the Caribbean tube sponge Aplysina archeri. In the lab, they were able to identify the threads as streams of mucus carrying waste. They emerge from the openings of the sponge, travel across the surface of the organism and aggregate into clumps that are released with a sneeze and quickly engulfed by other sea creatures.
When viewing the time-lapse footage for the first time, then Amsterdam bioinformatics graduate student and study co-author Yuki Esser was disappointed, believing that the movement she was seeing (i.e. sneezing) was simply a camera focus error. “I thought there must be a drop of water on the camera lens or something Something caused this,” she said. But she quickly realized it wasn’t a mistake.Once Ms. Esser and her colleagues discovered that they had taken nearly identical time-lapse videos of A. archeri On the coast of Curacao, recording footage “became a sport,” she said. “It’s like, ‘Maybe we sneezed again on camera!'”
The researchers believe that sneezing out waste-laden mucus is a common strategy used in sponges around the world. The study raises more questions, said Sally Rice, an evolutionary biologist at the University of Alberta and co-author of the study.
“Slime,” she said. “Is it similar to mucus from other animals? What cells are making it?” She also wonders what triggers the sneezing. “When we have a runny nose, we pull out Kleenex,” she said. “But how does the sponge know it’s time to sneeze?”
Studying the mucus may improve scientists’ understanding of how microbes and possibly disease spread in coral reef ecosystems, said Blake Ushijima, who studies corals at the University of North Carolina Wilmington, who was not involved in the new study. He’s also struck by what the research can teach us about our own evolution.
“This could give us an idea of how early life evolved from these soft, brainless things to these complex organisms building spacecraft,” Dr Ushima said.