Birds do it, reptiles do it, and humans do it with an almighty “achoo!” – It has now been seen that sponges can also sneeze, expelling accumulations of mucus-trapped particles onto their surface in the process.
The team behind the research said that while the aquatic organisms had previously been observed making contractions, which they had dubbed “sneezing”, the details of the process were unclear.
Now they have discovered that the contractions are involved in an unexpected form of waste disposal.
Dr Jasper de Goeij, a marine biologist at the University of Amsterdam and lead author of the paper, said the team made their discovery while examining timelapse videos of sponges to try to understand how the creatures pooped.
“We found many of the [ejected] material … it’s probably inorganic particles, meaning sand, sediment, things that the sponge can’t use that might just be clogging the system and have to get rid of it,” De Goeij said.
Sponges are a bit like chimneys in that they have long been thought to operate on a one-way system. Water, which contains nutrients, enters the body through tiny pores and is filtered, with excess water and waste materials dumped into a central cavity from where they are expelled through a single opening, called osculum.
But the latest study suggests another waste disposal system is at play.
Writing in the journal Current Biology, De Goeij and colleagues reported how they found the Caribbean stovepipe sponge, Aplysina archeri, it has a constant flow of mucus coming out of its pores against the feed stream, not unlike a runny nose, which carries particles with it.
The team says this mucus forms roads through the sponge, intercepting and moving particles to the surface in the process, resulting in the formation of stringy clumps. When the sponge sneezes, this particle-rich mucus is expelled into the environment.
“This is something we’ve never seen before,” said Professor Sally Leys, a sponge expert at the University of Alberta and co-author of the research.
What’s more, the team said, this mucus-rich material is subsequently fed on by other creatures.
“There are a lot of critters that would probably like some sponge mucus,” De Goeij said.
The authors suggested that particles must be removed from the creature’s pores and surface to prevent clogging of its filtration system.
“There has to be some evolutionary advantage to not having all these bits and pieces inside [organisms’ pores]Leys said, suggesting that one possible explanation is that they may damage the sponge’s filtering cells.
However, questions remain, including what exactly triggers a sponge to sneeze, how mucus moves, and how widespread the phenomenon is among sponges.
Although a sponge sneeze is different from a human sneeze, especially because sponges filter water instead of air and their sneezes take about half an hour, Leys said there are parallels , as both involve uncontrolled contractions to expel waste.
“What’s really interesting is that it’s kind of evolutionary basic,” Leys said.
Leys added that the study offered new insights into what a simple creature might look like.
“It’s a very sensitive and coordinated animal, despite not having all the features that you’ve grown up to understand that animals should have: front and back, eyes and tails and things like that,” he said. “He’s constantly behaving in a way that we can relate to.”
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