Birds do it, reptiles do it, and humans do it with an almighty “achoo!” – now it has emerged that sponges can also sneeze, casting off accumulations of particles trapped in mucus on 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 “sneezes”, the details of the process remained unclear.
Now they have found the contractions are involved in an unexpected form of waste disposal.
Dr Jasper de Goeij, a marine biologist at the University of Amsterdam and the senior author of the paper, said the team made their discovery while examining timelapse videos of sponges in a bid to understand how the creatures poo.
“We found a lot of the [ejected] material … to be probably inorganic particles, meaning sand, sediment, things that the sponge cannot use that are only maybe clogging the system and it needs to get rid of,” De Goeij said.
Sponges are a little like chimneys, in that they have long been thought to operate a one-way system. Water, containing nutrients, enters the organism through tiny pores and is filtered, with excess water and waste materials discharged into a central cavity from which they are expelled through a single opening, called the osculum.
But the latest study suggests there is another waste disposal system at play.
Writing in the journal Current Biology, De Goeij and colleagues reported how they found the Caribbean stovepipe sponge, Aplysina archeri, has a constant stream of mucus flowing out of its pores against the feeding current – not unlike a runny nose – carrying particles with it.
The team say this mucus forms highways across the sponge, intercepting and moving particles on the surface in the process, resulting in the formation of stringy clumps. When the sponge sneezes, this particle-rich mucus is ejected into the surroundings.
“That’s something we have never seen before,” said Prof 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 upon by other creatures.
“There’s many critters that probably would crave a bit of sponge snot,” said De Goeij.
The authors suggested particles need to be cleared out of the creature’s pores and off its surface to prevent its filtration system from becoming clogged.
“There must be some evolutionary advantage to not having all these bits and pieces go into the [organisms’ pores],” said Leys, suggesting one potential explanation is that they may damage the filtering cells of the sponge.
However, questions remain, including what exactly triggers a sponge to sneeze, how the mucus is moved, and how widespread the phenomenon is among sponges.
While a sponge sneeze is different to a human sternutation, not least as sponges filter water rather than 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 it’s sort of an evolutionary basic,” said Leys.
Leys added that the study offered fresh insights into what may appear to be a simple creature.
“It is a very sensitive and coordinated animal, despite not having all the characteristics that you’ve grown up to understand animals should have – fronts and backs, and eyes and tails and things like that,” she said. “It’s constantly behaving in a way that we can relate to.”
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