Reconstructing an evolutionary swim

By Christine Buckley, CLAS Today

Eric Schultz, professor in the department of ecology and evolutionary biology in the College of Liberal Arts and Sciences, has received a Fulbright scholarship to study the evolution of landlocked fishes in Greece.

Schultz’s work will investigate how fish species that were once only found in salt water have evolved to flourish in fresh water.

“I’m looking at a deep part of our own physiology,” he says. “We came from freshwater fish that once came from the oceans.”

What many people don’t realize about fish, says Schultz, is that they are in a constant state of disequilibrium. If they live in salt water, then their surroundings are saltier than they are, and salt is constantly trying to get into their bodies. Conversely, if they live in fresh water, then salt is constantly trying to get out of their bodies.

So, says Schultz, adapting to live in fresh water when your ancestors have lived in salt water for millions of years seems like a difficult task. But thus far, no scientists have tested exactly what it takes to make that transition.

“If you take an animal that has the historical ability to tolerate salt, how long does it take for that ability to disappear?” asks Schultz. “Is there a tradeoff? Do they get better at living in fresh water than salt water? ”

In Connecticut, Schultz studies alewives, a group of fishes that have historically traveled from salt to fresh water to spawn, but now also include some forms that live exclusively in fresh water. This summer, he’s testing the tolerance of different landlocked populations for living in salt water.

In the fall, Schultz will travel to Greece to work in the laboratory of Constantine Stergiou at the Aristotle University in Thessaloniki. About 10 percent of the freshwater fish in Greece have moved from salt water to fresh water, he says. Schultz will explore the challenge of living in a saline environment in these fishes.

Schultz will also spend time teaching at the university, giving lectures and conducting workshops in laboratory methods with undergraduate and graduate students. He’ll also visit with other scientists, and he hopes to forge collaborations for future research.

The most exciting thing about this work, says Schultz, is that he’s reconstructing the major evolutionary event that led to the formation of four-legged creatures – in his words, “recapitulating the swim upstream” of so many fish species.

“In the Silurian period (about 430 million years ago) aquatic areas were silty and didn’t offer much for vertebrates to live on,” he says. “But by the end of the Devonian (360 million years ago), fish were in fresh water and some of them were starting to grow limbs. Somehow, they made that profound change.”

“Half the fishes in the world live in fresh water,” he says. “And none of that would have happened if they hadn’t crossed the salt barrier.”

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