Temporary desert ponds yield a new family of water fleas

The small, murky ponds that come and go with the rain in Oregon’s Agate Desert are an unlikely hunting ground for biologists in search of new forms of life.

But three ephemeral ponds near Medford, Ore., have yielded a once-in-a-century taxonomic surprise: a new species of water flea that represents an entirely new family – a missing link of sorts – of water fleas.

Collected by a Nature Conservancy naturalist, specimens of the animal sat on a shelf in the laboratory of Stanley Dodson, a UW–Madison professor of zoology, for five years before they were dissected and identified as a new species representing a family of unknown water fleas.

“One hundred years after we thought we had everything there was at the family level, along comes this animal,” says Dodson, who, with former graduate student Carlos J. Santos-Flores, described the new animal in the scientific journal Hydrobiologia. “It is incredibly unlikely that you’re going to find anything new and different today because people have been out collecting these things in North America for more than a hundred years. That’s why this is a special animal.”

What’s more, the new water flea, known in scientific jargon as Dumontia oregonensis, may be a missing link, an animal with anatomical features shared by all the different branches of the water flea family tree.

“This animal resembles the predicted ancestral animal,” says Dodson, of the water flea, which measures about a millimeter and a half from antennae to tail. “It has characteristics of the major branches of the water fleas.”

The newfound water flea has six pairs of feathery legs that are most likely used to filter food – algae and bacteria – from the water. It also has a claw on its abdomen that’s used to clean debris from its food-snaring legs.

“It’s probably really good at catching fairly large protozoans, but that’s just a guess,” says Dodson, noting that next to nothing is known about the animal and how it behaves.

“All we know is that it occurs at three sites near Medford, Oregon. These are very shallow ponds and they are very temporary. They fill up in the winter and they only have water for a couple of months,” he says.

The ponds where the new water fleas were discovered are on land owned by the Nature Conservancy, and lie on the very edge of Medford in an area of low-density urban development. “This is not pristine wilderness, and if it were not for the Nature Conservancy, the ponds would be at great risk of being converted into something else,” Dodson says.

Although just visible with the naked eye, water fleas are critically important animals in their environments, playing two important roles in the ecological dynamics of freshwater ponds and lakes. One, they help maintain water quality because, often, they are able to check the growth of the algae that compose a big part of their diet. They are also an important source of fish food.

In shallow lakes, they are an important diet item for salamanders and birds, Dodson says.

“They are a keystone species. They are abundant, and they are at the center of the food web, ” he says.

Found in most corners of the planet, there are hundreds of species of water fleas existing in the world today. The tiny animals have an ancient lineage, the oldest fossils dating to more than 100 million years ago.