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Photo of crayfish with antenna and claws extendedIn the Society of Crayfish

It all started with a question shared among colleagues in an impromptu hallway discussion: Is there a biological basis for social structure, and, if so, what is it? In other words, how does Ed know Fred, and how do they use that knowledge to interact with each other and others of their species?

Like many scientific questions, this one didn't turn out to have a simple answer, but it did lead to intriguing research that has taken three UK researchers and a cadre of students into central Kentucky caves in search of crayfish that they believe will yield some of the answers.

Photo of Philip Crowley, Robert Ziemba and Robin CooperPhilip Crowley (left), Robert Ziemba and Robin Cooper

Philip Crowley, Robin Cooper and Robert Ziemba, all in the School of Biological Sciences, are in the midst of multidisciplinary research that explores the development of social systems from diverse perspectives. It is their integrative approach that offers such promise. Crowley has years of research in game theory and ecology, Cooper is a neurophysiologist interested in understanding the basis for behavior in a social system, and Ziemba, a postdoctoral scholar, is interested in sensory ecology (understanding how an animal uses sensory perceptions).

Collectively, they are able to blend physiological and behavioral perspectives to address the issue more comprehensively than has been done before. Their research will characterize the sensory structures and sensitivity to sensory stimuli in crayfish; compare the effects of chemical, tactile, and visual stimuli on the internal state and the behavior of crayfish; and determine the role of sensory information in the formation and maintenance of social structure.

"By using these organisms, one can understand how the nervous system functions and how it can alter the animal's behavior, thus affecting social structure," Cooper says. "This is applicable throughout the animal kingdom, including humans, since the basic structure of the nervous system of all animals is one that allows the animal to perceive information, process the information, and react accordingly."

"This is a very exciting issue within a social system," says Crowley. "We want to know if individuals can remember each other and for how long. If you see Fred every day, you may need to remember him, but if you don't see him very often, do you still remember him?"

Photo of crayfish preparing to fight"Obviously with crayfish, we can't ask Fred whether he knows Ed, so we have to get at it through physiological and behavior tests," Cooper adds. "We are setting up artificial groups and videotaping all the interactions in the lab. We can see who fights and who is submissive. We can see whether the crayfish tries to escape and we can note any posturing."

This research is carried out with two types of crayfish—a blind species (Orconectes australis packardi) found only in caves and a sighted species (Orconectes rusticus) that lives in surface streams. Studying the two species in tandem makes it possible for the researchers to study contrasting anatomical, physiological, behavioral, and social features, and ultimately understand the sensory mechanisms that evolved in the presence or absence of light.

Photo of crayfish locked in battle"There is a great deal of information on the two species we are using," says Cooper, who has extensive experience with crayfish in other research and enthusiastically suggested them for this project. "They are also easy to manipulate. Their behavior and dominance relationships can be readily observed and measured. We can test their vision, olfaction, and tactile sense in our research and determine how these factors affect their identifiable social structure."

In the lab the crayfish are kept in aquariums and small tubs of water. The researchers use what they call a "startle stimuli"—they drop a pebble in the water between two individuals, for example—to start the action. The animals have already been hooked up with electrodes so that the researchers can measure heart rate. "Determining their state of excitability gives us clues about the animal's aggressive and submissive behavior," Cooper explains.

The importance of the resulting interaction to the researchers is how the two species differ in terms of social structure. "We did experiments to compare the two species and have found interesting differences," says Ziemba. Crowley adds that the absence of vision gives the cave species far less information about the other. "With less information we'd expect a more irregular social structure."

A key behavioral trait being studied is dominance. Past research has found that social systems based on dominance seem to emerge from repeated interactions. Ed meets Fred for the first time. Both animals are capable of inflicting damage on the other. Each is either aggressively daring or careful and conciliatory during an interaction where a resource such as food or a mate is at stake. When both are daring, the result is dangerous combat. When both are careful, ordinarily the most persistent individual winds up with the resource. When one is daring and the other careful, the daring crayfish gets the resources and the careful non-combatant avoids adding injury to insult.

The question then is how they determine when to be aggressive and when to be careful in an initial interaction. Such factors as size, overall physical condition and memory play a role.

Crowley has developed a computer simulation model to evolve strategies for playing this "game." It is based on a mathematical approach (game theory—a mathematical analysis of contests) widely used in economics and now increasingly applied to ecology and evolution. The idea of "games" has become a scientific metaphor for a wide range of human and animal interactions in which the outcomes depend on the strategies of two or more players who have hostile or, at best, mixed motives.

Photo of blind species of crayfishThis blind species of crayfish is found only in caves.

"In the past 30 years, biologists have contributed the concept of evolutionary stability to game theory, the idea of finding strategies that, when adopted by members of a population cannot be beaten by a rare, alternative strategy," Crowley explains.

A computer, beginning with completely random, nonsense strategies, gradually evolves the most effective strategies using the principles of evolution by natural selection. Out of the games comes a social structure and an understanding of the most successful strategies. This research with the crayfish will further test his game theory. "One aim of our crayfish collaboration is to see if what the computer produces has some bearing on what these animals are actually doing in the lab and in the field," Crowley says.

"In this game, even the crayfish that can't see have other senses, other channels of getting information," says Ziemba. "The next step is to determine how important each channel is and how important the quality of information coming from that channel affects the outcome."

To do that, the researchers are using a variety of approaches with crayfish in addition to testing heart rate. They are using transmission electron microscopy to study the structure of the nervous system, and taking direct electrophysiological recordings. Those recordings measure sensory sensitivity.

"The blind crayfish may have some ability to sense light," Ziemba says. "For example, it may be able to sense light with receptors on its tail fan. There is also the issue of smell. A crayfish may smell different to another crayfish if it is a dominant individual." These tests may ultimately help the researchers discover whether crayfish can recognize each other, and if so, how that affects the establishment of social structure.

To quantify the results, the researchers are using a type of round-robin tournament, pairing individuals, forcing them to interact, and then recording their behavior. Results from these interactions are then compared to computer models using game theory to determine if the predictions based on game theory are correct.

The interactions are part of what Crowley and others call the evolution of cooperation, a concept that has broad implications to other species, including humans.

"Why do we see cooperation within species?" he asks. "Natural selection would suggest that the individual would cheat when it is to his or her advantage, yet we see cooperation in nature. The human social system is built around this kind of issue."