Frog Man of the Bio Labs

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December 02, 1999

SEARCH THE GAZETTE

HARVARD GAZETTE ARCHIVES

By Ken Gewertz
Gazette Staff

Professor of Biology James Hanken displays a marine toad at the Museum of Comparative Zoology. "There's a tendency to think that our knowledge of the identity of the basic biota is pretty complete . . . in fact, we have documented less than one-half of the world's biota." Photo by Rose Lincoln

The shoebox-sized plastic containers sit on shelves in a climate-controlled room in the Biological Laboratories. James Hanken takes one down and opens the lid. Inside are several tiny toads, squatting in a shallow pool of water.

Their splotchy bodies are green and black on top, red and black on the bottom – hence the name: Oriental fire-bellied toad. Hanken picks one up to demonstrate its varied coloration, then promptly washes his hands.

"Their bodies exude a poisonous substance," he says. "We have to change their water frequently or they’d poison themselves."

Hanken has done a good job of ministering to the toads’ needs. Some of the little critters have been in his care since 1981.

Hanken, a developmental and evolutionary biologist specializing in amphibians, recently joined the Department of Organismic and Evolutionary Biology (OEB) as Professor of Biology in the Faculty of Arts and Sciences.

According to chairman David Hartl, Hanken brings unique gifts to the department:

"The strength of Hanken's work lies in its broad comparative approach," Hartl says. "He has no equal in his ability to unite an encyclopedic knowledge of how morphology changes during the course of development with new techniques that deal with the factors governing these changes."

Hanken describes his work as "empirical" and "lab- and fieldwork-oriented." His research on fire-bellied toads offers one example of this approach. He has been studying these tiny vertebrates in order to identify the cells in the embryo that develop into specific structures in the adult animal.

Techniques that have been developed in the past 10 years allow Hanken to inject embryonic cells with a fluorescent marker and follow their progress through the course of development. Using this method, he has been able to shed light on subjects that have intrigued biologists for more than a century, such as the development and organization of the head in vertebrates.

"The organization of the head was a hot topic in the 19th century," Hanken says. "We’re still working on it. What’s exciting these days is that we have an array of tools and techniques that Darwin could only dream of."

Hanken’s research hearkens back to one of biology’s most venerable – and contested – claims: ontogeny recapitulates phylogeny. Simply put, this means that the way an organism develops from embryo to adult mirrors the evolution of the larger group of which the organism forms a part. This link between developmental biology (or, as it used to be called, embryology) and the study of evolution is something that biologists have begun to pay renewed attention to in the past 20 years.

"Developmental processes offer insights into the evolutionary history of organisms that one couldn’t gain otherwise," Hanken says.

Not all aspects of evolution are explained by natural selection, he explains. Natural selection, or the dominance of certain variations as a result of environmental pressures, is essentially a culling process.

"Natural selection acts on an array of variation that already exists, but what if that array is limited somehow? If a variant isn’t produced, natural selection can’t favor it. How an organism develops is one factor that precludes certain forms from occurring," he says.

As a way of testing this hypothesis, Hanken has conducted research on one of the world’s smallest vertebrates, a tiny Mexican salamander known as Thorius schmidti. By examining bones in the animal’s limbs, Hanken has revealed some of the ways in which the forces of development and natural selection interact in this amphibian species.

Another aspect of Hanken’s work involves the identification and naming of species, a science known as taxonomy or systematics.

"There’s a tendency to think that our kno wledge of the identity of the basic biota is pretty complete," he says. "But, in fact, we have documented less than one-half of the world’s biota."

For example, within the past 10 to 15 years alone, the number of named species of living amphibians has increased by 20 percent.

Most of these identifications have occurred as the result of field surveys, although some come about when a pair of sharp and expert eyes search through an established collection.

"I just found a new species of salamander in the MCZ’s herpetological collection that had been misidentified by accident," Hanken says. "It was collected about 20 years ago, and it was just sitting there minding its own business." (The herpetological collection at Harvard’s Museum of Comparative Zoology [MCZ] is the largest of any university collection in the world.)

Hanken, 47, grew up in New York City and earned his bachelor’s degree from the University of California at Berkeley in 1973. He remained at Berkeley and earned his Ph.D. in zoology in 1980.

The author of numerous scholarly articles, Hanken is also the editor (with B.K. Hall) of a three-volume work, The Skull (University of Chicago Press, 1993). Before coming to Harvard, he was a professor in the department of environmental, population, and organismic biology at the University of Colorado, Boulder.

When asked about the key experiences that led to his choosing a career in the biological sciences, Hanken points to the summer he spent as a "turtle turner" on a remote beach in Costa Rica during his college years.

The beach was a site where giant sea turtles come ashore annually to lay their eggs. Hanken was one of several college students connected with a program at the University of Florida, which monitored the turtle population. His job was to grab the 350- to 400-pound female turtles after they had finished laying their eggs and turn them over on their backs so that field wor kers could measure and tag them. He still has a turtle skull he found on the beach, which he passes around in his biology classes for students to examine.

"It was the best summer of my life," Hanken says.