With tissues in hand, Danielle Ludeman has spent countless hours watching sponges sneeze. It may seem strange, but the sneezes point to evidence of a sensory organ in one of the most basic mulitcellular organisms on Earth.

"The sneeze can tell us a lot about how the sponge works and how it's responding to the environment," said Ludeman, a master's student at the University of Alberta. "This paper really gets at the question of how sensory systems evolved. The sponge doesn't have a nervous system, so how can it respond to the environment with a sneeze the way another animal that does have a nervous system can?"

A sponge relies on water flowing through its body for food, oxygen and waste removal. The "sneeze," is actually a 30- to 45-minute process in which the sponge's entire body expands and contracts.

Time-lapse sneezes

For their study, Ludeman andbiologist Sally Leys, used drugs to elicit sneezes in freshwater sponges and observed and recorded the process using fluorescent dye and a video camera. Their efforts focused on the sponge's osculum, which controls water exiting the organism, including water expelled during a sneeze.

"Through a series of lab experiments, the pair discovered that ciliated cells lining the osculum play a role in triggering sneezes. In other animals, cilia function like antennae, helping cells respond to stimuli in a co-ordinated manner. In the sponge, their localized presence in the osculum and their sensory function suggest the osculum is in fact a sensory organ," according to a press release announcing the findings.

"For a sponge to have a sensory organ is totally new. This does not appear in a textbook; this doesn't appear in someone's concept of what sponges are permitted to have," said Leys.

Leys said the discovery questions how sensory systems may have evolved in the sponge. It's possible this sensory system is unique to the sponge, she said, evolving over the last 600 million years. Or it may be a common mechanism shared among all animals, and retained over evolutionary history.

Despite all the hours filming and observing sneezes, Ludeman says she's still not sick of sponges.

"We know so little about how a sponge works, and there are so many cool questions you can ask."

Ludeman and Leys's findings were published in BMC Evolutionary Biology.