Shortly after the lights dimmed and the giant green sponge appeared on the movie screen, a hush fell over the audience. It turns out, the sponge represented the freshwater variety and was just one of five sponge species living in Montana.
While the slide was only the first of many to come, it provoked several questions from the audience. Was the sponge a plant or an animal? Could you eat it? Does it have any medical or industrial uses? Is it slimy or gooey when you touch it?
Carroll College biology professor John Addis, a sponge expert, answered those questions and more at a Last Chance Audubon Society meeting, held last week at the Lewis and Clark Public Library.
For the past 10 years, Addis, along with help from various Carroll students, has searched Montana’s lakes for sponges. The creature is considered one of the simplest multi-cellular animals on Earth, if not the most overlooked.
The organism may also have undiscovered medical and environmental qualities that Addis and his students are now beginning to explore.
“I haven’t had a lifelong passion for sponges,” Addis said, grinning in the glow of the slide projector. “Early one summer I went out to see if I could find any sponges, and after spending three or four days looking for them, I finally stumbled across some in Salmon Lake.”
Addis has since identified five species of freshwater sponges in Montana, some living at elevations as high as 9,000 feet.
Most varieties live near the outlets of clear lakes where they capture nutrients from the water. Some species grow on rocks. Some prefer submerged sticks and the underside of soggy logs. One rare species thrives on lake-bottom silt.
“We’ve got sponges growing on all kinds of surfaces,” Addis said. “The outlets of lakes are the best place to find them. You need some flow, but if the flow is too fast it tends to be detrimental to their growth.”
With their leafy tendrils and mostly green hue, Montana sponges resemble a plant. Some appear as goop in the water, a blob of algae or fungi fixed to a stone. They have no mouth, no organs or tissue to speak of. They don’t have blood and they don’t really move.
Yet Addis and the rest of the scientific community say the sponge is an animal. DNA sequencing places them in the animal class, though they’re well at the bottom when it comes to complexity.
“There’s a lot of evidence that says sponges are animals and not plants,” Addis said. “The basic definition of an animal is an organism that takes its food in by ingestion.”
The sponge eats through a series of tiny pours called “ostium,” which filter passing nutrients from the water. Once the nutrients are pulled into the sponge, flagella draw the particles deeper into the animal’s collector cells.
“The digestive system is totally different than the animals most of us are accustomed to,” Addis said. “The sponge takes in particles and breaks them down in its cells. It’s real primitive, and there aren’t too many animals that handle food that way.”
Addis talks enthusiastically about his studies. He turns at one point to the image on the screen and points out several odd features.
“You can see how this sponge here has grown nubs,” he said, pointing to the finger-like protrusions sprouting from its girth. “It has variation in structure and form.”
The sponge is so different from the rest of the animal kingdom it appears almost alien in design. It’s also quite complex when viewed at a molecular level, which is what Anisha Boetel, a chemistry major at Carroll College, spent her summer doing.
Boetel, who plans on going to medical school, examined the sponge’s ribosomal RNA. The point, she said in a Carroll science lab, was to look for RNA folding patterns that distinguish one sponge species from the next.
“It amazes me that an animal so simple can be so complex.” Boetel said. “If you look at something just on the surface, it looks simple. But as you break it down, you begin to see differences. You can always go deeper.”
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The fossil record suggests that marine sponges emerged 750 million years ago, predating by almost 200 million years the so-called “Cambrian explosion,” when most multi-cellular animals came into existence.
Dinosaurs, in comparison, ruled the earth 250 million to 65 million years ago. Homo sapiens appeared a mere 195,000 years ago.
Evolutionary biologist Mitch Sogin of the Marine Biological Lab at Woods Hole, Mass., began studying the genetic coding of simple marine life in the mid 1990s. He wanted to isolate the single life form that gave rise to the rest of the animal kingdom.
Recently featured in a National Geographic news article, Sogin’s work points the evolutionary tree at the sponge. Many scientists, including Addis, believe the sponge — in particular its larval form — likely gave rise to animals.
“One of the difficulties is explaining how an organism like an adult sponge could be so different and yet give rise to other animals,” Addis said. “It’s the larval form of the sponge that’s really critical. It’s been suggested that sponge larvae show more affinities to other animals than the adults do. The larval form is more typical of animals.”
The problem with the adult sponge, Addis said, is really a problem of classification. Sponges vary in color, shape and size, so the qualities don’t really help when identifying or classifying the organism.
To do that, Addis turns to something much more telling. A new slide appears on the screen. While it looks like the spine of a sea urchin, it’s actually a “spicule” magnified many times.
Made up from silica, the spicule represents the sponge’s skeleton. Its texture and shape can be used to separate one sponge species from the next. When you bathe with a sponge, Addis points out, you’re bathing with its skeleton — thousands of tiny spicules scrubbing your body.
“By and large, sponges are not preyed upon because their spicules are considered irritants,” Addis said. “Some sponges also have a natural chemical defense that protects them.”
In the ocean, certain sponge varieties possess anti-tumor compounds. Others have anti-bacterial compounds. Their chemical defenses help prevent other organisms from over-growing them, or simply eating them.
Danielle Daehnke, a biology major at Carroll College, worked last summer in the field collecting sponge samples taken from Salmon Lake.
In the lab, the samples were crushed and mixed with various solutions to see what, if any, medicinal compounds the freshwater sponges might hold.
“We wanted to see if there was anything that could be used as an anti-biotic, an anti-bacterial, or anti-tumor,” she said. “We found some anti-tumor qualities.”
Even so, Daehnke said, the process will be repeated several times to see if the results come out the same. If they do, it doesn’t necessarily mean the anti-tumor agent has any medical uses. That, she said, would require more tests and further studies.
Sponges may be useful beyond the medical realm. Some species are being used for environmental cleanup. They can filter toxins from the water, including heavy metals like lead and cadmium. In Australia, they’re used to filter nitrates from the water.
“Are they gooey or slimy?” someone in the audience asked.
“Most sponges are not slimy to the touch,” Addis answered, turning to the screen. “But the consistency of the sponge varies. This sponge here has quite a dramatic tint to it, making it easy to mistake as a plant.”
“Why is it green?” someone else asked.
“The green color seen in many freshwater sponges is from the algae taken up by the sponge,” Addis said.
Daehnke, who plans on entering the Peace Corps after graduation, further described the sponge with flair. “When you touch them, they feel like a sponge. They have that crunchy, squishy feel to them.”