UT neuroscientists discover how fish send short electric signals

Elizabeth Robinson

University of Texas neuroscientists have discovered how the baby whale, a species of fish, uses electrical impulses to navigate murky waters.

Their paper, published in the journal Current Biology on June 21, aims to help biologists understand how genetic changes allow creatures to evolve highly complex organ systems.

“What makes the cell so interesting is that electric fish use these electric organs to emit the electricity, and then they sense the electricity that they make,” UT neuroscience professor Harold Zakon said. “They can detect the world around them in total darkness … There are a lot of parallels with echolocating bats.”

The team’s discovery helps evolutionary biologists understand how complex organ systems appear in the animal species we see today, Zakon said.

“We like studying electric fish because they show (lots of) evolutionary innovations,” Zakon said. “They not only have an electric organ (which) comes from muscle cells, they also have special sensory cells that are related to hair cells (which we use in our ears) for hearing and balance. In addition, they have special parts in their brains to receive this information and process it.”

The baby whale, whose scientific name is Brienomyrus brachyistius, uses a modified version of the same ion channels that create electrical impulses in neurons and hearts, Zakon said. A gap in the organ’s insulation lets the electricity flow out into the water, where sensors on the fish’s skin can then pick up the signal again.

In addition to sensing both living and nonliving things around them, the fish can also use the electricity to communicate with and identify each other, said Swapna Immani, a UT research associate on the project.

The blasts of electricity are also very brief so predators can’t detect them, Immani said. This left the researchers wondering how the creatures could make their impulses so brief.

“It takes some amount of time for the (ion channels) to change their conformation,” Zakon said. “So if you’re producing a signal of a few hundred microseconds, it gets to the point where the proteins can’t move much faster.”

The scientists looked at the gene sequence and found an unusual variation in an area they thought was highly uniform among ion channels, Zakon said. They placed this short section into the gene for a more standard ion channel and found that it functioned just as it did in the fish.

“We were able to show that the behavior of this channel changed entirely dependent on (this short sequence),” Zakon said.

Electric organs such as these have evolved at least eight times independently, Zakon said. Sometimes similar adaptations evolve in different ways, but other times there is only one pathway to those adaptations, he continued.

“We can ask, ‘If something has evolved multiple times, did it take the same path or different paths?’” Zakon said. “We keep seeing a lot of the same things happening multiple times (in electrical organs in fish), so there might only be a few paths to get to the same end.”

One of the biggest challenges of evolutionary biology is finding out how changes in genes lead to changes in the body, Immani said.

“Looking at these fish and looking at the changes they have evolved in the channel could give us a sense of how these (adaptations) arise,” Immani said.