Wednesday, April 14, 1999

By Craig T. Kojima, Star-Bulletin
Researchers April Davis, from left, Dan Hartline, Tina Carvalho
and Petra Lenz hold photos of copepods, the tiny
sea animals they have been studying.

Tiny sea critter
yields big discovery

UH researchers' work on
copepods illuminates how
nervous systems evolve

By Helen Altonn


Biology textbooks may have to be revised because of a discovery about a tiny sea animal by University of Hawaii researchers.

An article in Nature magazine today reports findings that could change basic data concerning differences between vertebrates and invertebrates.

Petra Lenz, an ecologist, and her husband, Daniel Hartline, a neurophysiologist, both at the Pacific Biomedical Research Center, are studying calanoid copepods -- insectlike invertebrates smaller than the tip of a fingernail, under 0.12 inches.

By Craig T. Kojima, Star-Bulletin
Above, a close-up of a copepod, which is smaller than
the tip of a fingernail, under 0.12 inches.

They are extremely abundant crustaceans (related to crabs and lobsters) at the bottom of the food chain, the scientists said yesterday.

"Although most people wouldn't recognize copepods, if you go swimming they're all around you," Hartline said. They tend to be clear but can be seen with the naked eye, he said. "They're fascinating to look at."

Nerve coating a new find

Even more fascinating, the researchers discovered that the nerve cells of some species are coated with myelin, a white fatty substance that was considered mainly "a vertebrate invention," Hartline said.

Until now, myelin was known to exist only in humans and other vertebrates and isolated invertebrates -- earthworms and prawns and shrimp, he said.

Myelin coating on the nervous system and nerve fibers acts like insulation on an electric wire, the scientists said.

"It greatly speeds up the nervous system so the time for communication between distant parts of an animal are shortened quite a bit," Hartline said.

The scientists said April Davis, their research assistant and an animal sciences graduate student, discovered myelin circles around nerve fibers in copepod cross-sections and did "all the hard work" involved in the finding.

Tina (Weatherby) Carvalho, researcher and electron microscope supervisor, had seen the layers earlier but thought they were anomalies, often caused by the chemical fixation material used on the tissue, the scientists said.

Davis and Carvalho confirmed the results by preparing samples with an ultra-rapid freezing technique.

Coating allows quick reaction

When the two told Lenz and Hartline of the myelin finding on April 1 last year, the husband-wife team thought it was an April Fool's joke.

"It's a really radical notion," Hartline said. "Nobody had been aware of this in any sense."

In fact, they had been arguing about the animals, Lenz said. She thought some seemed slower than others, and Hartline speculated that they might be sick. "She was right and I was wrong," he said.

But not all free-swimming copepods have myelin coating, the researchers have found. "Only a few very abundant groups are myelinated," Lenz said. And they're the ones that evolved most recently, Hartline added.

Those that developed myelin appear to live in more exposed, riskier habitats in the open ocean and need to react faster to predators, he said.

The scientists observed that Undinula vulgaris, a copepod species in Kaneohe Bay, responds to stimuli about 100 times faster than humans.

They calculated in behavioral studies on the animals that even the slowest, without myelin coating, can react to a stimulus and escape in six milliseconds, Hartline said.

Those with myelin get away two milliseconds faster, he said. Although that "sounds like nothing at all," he said, "for a tiny animal like a copepod, two milliseconds is a big deal. They're amazingly fast."

Those with myelin also protect themselves generally by living at ocean depths during the day to avoid preying fish, the scientists said. The myelinated copepods swim to the upper layers at night to feed, then swim back.

Distribution now clearer

The finding has significant implications for the study of evolution, physiology and biology of the oceans.

Lenz said distribution of the tiny invertebrates has been recorded in literature for 50 years, but the reasons weren't known.

"We have found at least a partial explanation why they distribute themselves the way they do. ... That's the excitement," she said.

Copepods as a group are extremely significant because they're the most abundant multicellular animal on the planet -- more abundant than vertebrates, Hartline said.

"In a way it's just a technical wrinkle on these biology textbooks to the extent that they get into the issue of myelin at all," Hartline said.

But the animals are important as part of the food chain, he said. Fish and shrimp depend on them for a food source, he said. "So anything we can contribute to understanding the ecology of these animals ... is really important for understanding and managing ocean resources."

Also, Lenz added, "This is one piece of information you would want to know about your animals to have any kind of predictive ability (for global ocean changes)."

From a physiology aspect, she said the discovery will lead to a change in thinking about how nervous systems are organized on a large scale.

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