AMSTERDAM, Netherlands — The origin of sneezing dates back more than 600 million years — to the humble sponge, according to new research. An involuntary release of air helps these creatures get rid of irritants, just like humans, according to a team in the Netherlands.
The immobile aquatic animal is our earliest ancestor. Sponges have been around since the Precambrian era, a kind of evolutionary dark age. Now, a study has found ejecting mucus is the oldest way for organisms to discharge waste.
It expels material sponges cannot use. Unlike humans, however, other animals who share the environment dine on it. Sponges “sneeze” to unclog internal filter systems that capture nutrients from the water. They have been around since the dawn of complex life.
“Our data suggest that sneezing is an adaptation that sponges evolved to keep themselves clean,” says senior author Jasper de Goeij, a marine biologist at the University of Amsterdam, in a media release.
Sponges also have dense-yet-porous skeletons and specialized cells highly adapted to their environments.
“Let’s be clear: sponges don’t sneeze like humans do. A sponge sneeze takes about half an hour to complete. But both sponge and human sneezes exist as a waste disposal mechanism,” adds de Goeij.
As water passes through a sponge’s absorbent exterior, it receives oxygen and expels waste. Inside, tiny hairlike structures called flagella create currents to filter bacteria out of the cells and trap food within.
Strong skeletal structures help withstand the high volume of water that flows through them each day. They draw in and eject it from different openings, and sometimes will suck in particles that are too big.
“These are sponges; they can’t just walk to somewhere else when the water around them gets too dirty for them to handle,” the researcher explains.
This is when the “sneezing” mechanism comes in handy. The Dutch team captured on video mucus slowly being released through water inlets. The waste accumulates at the surface of the sponge. Occasionally, tissue will contract and push the mucus into the surrounding water. While it may be waste to sponges, fish who live around them think otherwise.
“We also observed fish and other animals feeding off of the sponge mucus as food,” says first author Niklas Kornder, a doctoral researcher in de Goeij’s research group. “Some organic matter exists in the water surrounding the coral reef, but most of it is not concentrated enough for other animals to eat. Sponges transform this material into eatable mucus.”
The study recorded “sneezing” in two species, the Caribbean tube sponge Aplysina archeri and a member of the genus Chelonaplysilla from the Indo-Pacific.
“We actually think that most, if not all, sponges sneeze. I’ve seen mucus accumulate on different sponges while diving and in pictures taken by other scientists for other purposes,” says Kornder.
However, researchers say there are still many aspects about sponge sneezes that remain open questions.
“In the videos, you can see that the mucus moves along defined paths on the surface of the sponge before accumulating. I have some hypotheses, but more analysis is needed to find out what is happening,” Kornder continues.
Sponges have no brains, neurons, organs, or even tissues, but recent research has also found they carry the beginnings of a nervous system. They have the genetic components of synapses and their versions share startling similarities with those of humans. Synapses are junctions between two nerve cells that are allow them to pass signals to one another.
“There are a lot of scientists that think that sponges are very simple organisms, but more often than not we are amazed by the flexibility that they show to adapt to their environment,” says de Goeij.
Sponges come in a wide variety of shapes and sizes and are often mistaken for plants. Different colorations may protect them from the sun’s harmful ultraviolet rays. There are around 8,500 living sponge species scientifically classified in the phylum Porifera.
They are completely distinct from corals, which require saltwater to survive. Most sponges are found in the ocean. They are important inhabitants of reef ecosystems, but others live in fresh water and even estuaries.
The study is published in the journal Current Biology.
South West News Service writer Mark Waghorn contributed to this report.