Crustaceans Struggle for Dominance

Most people come to Boston to eat lobster.

One Harvard graduate student, however, came here to study them.

Wendy A. Weiger '83, an M.D./Ph.D. candidate at Harvard Medical School, is studying the roles of hormones in the dominance hierarchies of New England's favorite shellfish, Homarus americanus.

Lobsters, according to Weiger, engage in violent encounters when placed in a confined space. These encounters take the form of antennae whips and pushing and shoving of claws.

When the struggle between the animals is over, one of them has emerged as dominant, and the other as subordinate. The dominant lobster will stand over the subordinate, which will crouch low to the ground and retreat.

These responses, said Weigher, are probably caused by the release of one of two neurotransmitter substances, of the class amines, known as serotonin and octopamine.

Initial experiments concluded that direct injection of the two amines did not, however, affect the muscles in different ways. Instead, they "primed" the muscles, and made them more responsive to stimuli, Weiger said.

Why Opposing Postures?

Researchers, under the direction of Edward A. Kravitz, Berry professor of neurobiology at the Medical School, then hypothesized that the opposing postures had to be generated by indirect actions of the two amines in the nervous system, whose cells then controlled muscle action.

The team, including Weiger, then tested this hypothesis by applying the substances to cells in the ventral nerve cord, and opposing postures were in fact generated.

At that point, researchers began attempting to identify all of the nerve cells which contained serotonin. When they did in fact find the 120 cells that contained serotonin, it turned out that these cells did not cause the lobsters to assume either posture.

Instead, Kravitz's team found a pair of large serotonin-containing cells, which, when stimulated, bias the system towards either stimulation or inhibition of the muscles involved in the postures.

Currently, Weiger is studying these "master cells." The entire nerve cord is removed from the animal, and the cells are then impaled with electrodes which measure their responses when various solutions containing the amines are passed over them.

This is just one of the facets of the project, said Weiger.

"We are trying to bring in as many approaches as possible," she said. "We are interested in gaining a model of behavior."

To do so, researchers will be pursuing two lines of research. One of these will be concerned with the examination of the inner workings of the lobster's nervous system, while the other will be a quantitative analysis of the animal's behavior.

"The time is coming when we need to bring together basic science and behavioral pharmacology," said Weiger, who plans to enter the field of psychiatry when she finishes her medical training.

Weiger said that the lobster model may be applicable to human hormonal systems as well. Octopamine is the lobster's analogue to the human amine norepineophrine, and serotonin occurs in humans. Both of these substances, along with dopamine, have been implicated in depression, schizophrenia and Parkinson's disease.