Perspectives Online

Model Bee-havior, An insect genomics specialist studies the why of what bees do. By Terri Leith

Honey bees have a broad range of complex behaviors, and Dr. Christina Grozinger (above) is studying how the queen-bee pheromone affects expression of the genes determining roles bees perform in the colony.
Photo by Daniel Kim

Bees do it,” wrote Cole Porter in 1928, ruminating in song on the romantic behavior of birds, bees and even educated fleas. Now Dr. Christina Grozinger is getting to the molecular basis of the behavior implied in those lyrics: She's looking at what honey bees do and, genetically speaking, why.

Grozinger joined the Department of Entomology, College of Agriculture and Life Sciences, in September 2004 as assistant professor. At the same time she became a member of the W.M. Keck Center for Behavioral Biology as a specialist in insect genomics. There she shares her findings using functional genomics to discover genetic bases for honey bee behaviors. What she learns can reveal much about how those same genes affect behavior in other species.

“Although the honey bee has long been a model for behavior in general - Karl von Frisch got the 1973 Nobel Prize for studying bee dance language - it is not a traditional model for behavioral genetics,” Grozinger says. “It's a field that's just starting. So I feel like I can make a lot of contributions.”

The arthropod genomics specialist position keeps Keck Center activities in step with the emerging field of insect genomics. “Functional genomics in general is becoming a much more powerful tool that a lot more people are using,” says Grozinger, referring to the microarray technology, available at the College's Genome Research Laboratory, that enables scientists to view the actions of thousands of genes at once and clarifies how genes interact.

“Microarrays now allow you to look at gene expression in an organism, at a snapshot of what genes are being used at a certain time,” says Grozinger. “Basically that means you can start studying the genes in organisms that are not traditional genetic models. Now people in many fields, such as entomology, can use this tool.”

Researchers in the College's Genetics Department also now use microarrays to study gene expression patterns in their research of Drosophila (fruit flies).

“But with honey bees, there is a range of other behaviors you can start to look at because they have a much more complex life and behavior patterns,” says Grozinger. “You can look at things like social regulation of behavior through pheromone communication, division of labor in a colony, what happens when they age, what happens after they mate.”

The genes have the same molecular functions in different systems, but because those functions may be subtle or specialized, they have not yet been found through traditional screens in the traditional model organisms. “But with bees,” says Grozinger, “we can study a broader range of behaviors that might finally help identify these genes.”

For example, the forager gene, whose expression will result in a worker bee behavior of foraging for food, is a gene that was initially found in fruit flies. “That was a case where they had one gene and already knew something about its function; it had been identified in a traditional genetic screen in a traditional research organism,” says Grozinger. “But now, with the microarray technique, we can look at these genes in bees and then look and see if they're doing the same things in flies and other animals.”

This could mean looking at thousands of genes, so the question is how do you know which ones are actually involved in a certain behavior? “Once you get all these genes with changes in expression levels, you first do a pattern analysis, to find groups of genes that are doing the same thing, and then do a functional analysis, where a few are studied in detail,” she explains.

Grozinger received her 2001 Ph.D. in chemistry from Harvard University. She came to N.C. State from the University of Illinois/Urbana-Champaign's Entomology Department and Neuroscience Program, where she was a Beckman Institute Fellow in the laboratory of Dr. Gene E. Robinson. It was there that Grozinger's studies of specific genes involved in honey bee behavior led to the discovery that pheromones (chemicals produced by a species that stimulate other members of the species) produced by the queen bee could direct or suppress the expression of genes determining certain behaviors associated with various hive roles of worker bees.

Now at N.C. State she is continuing the studies she began in Illinois. “My main project is to look at how pheromones change behaviors in bees, and they're a great model for that, because, unlike other model organisms, they have a lot of identified pheromones which regulate a lot of different behaviors,” she says. “So pheromones are great tools to turn off and on the behaviors we're interested in.”

Because honey bee colonies are so large (there can be up to 50,000 workers) pheromones are essential to communications that, by touch and smell, radiate out from queen to colony — and to the gene expression that determines the roles workers perform.

In fact, honey bees are perfect models for studying the genomics of insect social activity because they have so many well-defined behaviors. Grozinger wants to know more about what makes bees move from one behavioral role to another, what makes a bee's reaction to a pheromone result in one behavior at a young age but a different behavior at another age — or even shift back to a previous role if hive events transpire that affect workforce requirements for certain jobs.

And honey bees do a lot of jobs — they're not called “workers” for nothing.

The worker bees are nurses. They're foragers. They're builders. They're undertakers. And workers are all female. In this matriarchal society the males are drones whose only function is to mate with the queen and then die.

For the first 10 days of their lives, workers are nurse bees. The queen lays the eggs inside the honeycomb and the nurses care for the larvae developing in the honeycomb and regurgitate food to them. So basically the workers rear their sisters. When the larvae get old enough that they're ready to pupate, the nurses will extrude a wax cap over the cell so that they don't desiccate.

After the first 10 days, when a bee is “middle aged,” she will go from being a nurse to a specialized in-hive role. She might store the food, packing collected pollen into the honeycomb. She may build the comb, for which purpose workers develop wax glands on their abdomens. At that time she also may become a guard bee, which means she basically sits in front of the colony and looks for signs of danger, or do undertaking — piling up bee corpses.

Then when workers are about three weeks old, they switch to foraging, which they do till they die, at about age six weeks. The worker bees live for six weeks in summer or for three to four months in winter, when they're somewhat dormant.

(“Queen bees actually live about two years,” adds Grozinger. “There's a lot of interest in doing research comparing queens to workers because they're genetically the same - they have the same genome - but one lives more than 10 times longer.”)

This division of labor process has a built-in flexibility factor, with worker bees switching roles on an as-needed basis, “depending on what's going on in the colony,” Grozinger adds. “For example, if you take out all of the foragers, the nurse bees will switch into foragers when they're six days old as opposed to three weeks old. And then if you take out the nurse bees, some of the foragers go back to being nurses, re-growing the glands that they need to extrude.”

Grozinger is looking at the genetic basis of all this to figure out how pheromones affect gene expression and cause behavior shift: “I'm asking how you go from smelling this chemical to producing this behavioral response,” she says. “On top of that, why would you respond differently to the same pheromone at different stages of life?”

In her research, she has exposed workers to pheromones and looked to see what genes changed expression. “About 2,500 of the 7,000 genes we looked at were consistently changing. You can break them down to patterns to see what genes were being regulated together. I looked at nurse and forager genes. The queen pheromone was turning on the nurse genes and turning off the forager genes, which matches what the queen pheromone does in the colony. It keeps bees in the nursing state longer, so they become foragers when they are older. Also we are looking at what the individual genes are doing and how they are altering the brain to alter behavior.”

This is basic research, she says, offering insights into how the brain is functioning and the internal cues for behavior. “These genes are seen in all organisms, so the models we get out of this will be applied to different systems,” says Grozinger. “And now we can look at these genes in a range of species and make conjectures about the evolution of social behavior.”

Dr. Yongliang Fan (left) and graduate student Patrick Fischer (right) assist Grozinger in her lab. She hopes that more graduate students will soon join their research team.
(Photo by Daniel Kim)
Grozinger is also collaborating on an insect reproduction project with Dr. David Tarpy, assistant professor in the Department of Entomology. The two are looking at molecular mechanisms regulating the changes in behavior and physiology that occur after honey bee queens have mated.

“Mated queens no longer take mating flights but stay inside the colony, produce different pheromones than they did before mating and start laying eggs,” Grozinger explains.

What she and Tarpy discover from studying the genetic basis of a mating queen's behavior, and what's going on internally in the female, could have applications in pest management.

“This is a new, interdisciplinary field with so many opportunities,” Grozinger says, noting the recent creation here of the North Carolina Honey Bee Research Consortium, which includes as members Dr. Olav Rueppel of UNC-Greensboro, Dr. Susan Fahrbach of Wake Forest University and Dr. Stan Schneider of UNC-Charlotte.

Grozinger also will work with Dr. Trudy Mackay of the Department of Genetics, Keck Center director Dr. Robert Anholt, and Dr. Coby Schal and Dr. Fred Gould of the Department of Entomology. She'll take part in interdisciplinary collaboration with other Keck Center colleagues and at the Genomics Research Facility on Centennial Campus, the Bioinformatics Center, the Department of Statistics and the Genome Sciences Program.

Research associate Dr.Yongliang Fan and biochemistry graduate student Patrick Fischer assist in her lab in Gardner Hall. Grozinger is also looking for other graduate students to join her team, and there will be openings for undergraduates to be hourly assistants in the summer.

The place will be humming with the exploration of the honey bee behavior. Or, as Cole Porter would have it: that voodoo that they do so well.