Honeybee Sequencing: One Honey of an Idea
The little buzzers are a magic well for discoveries in biology | By Myrna E. Watanabe
In late May, the National Human Genome Research Institute (NHGRI) released its priority list of organisms under consideration for entry into the sequencing pipeline: One was the honeybee. It was a move that has numerous supporters. "We feel that sequencing [the bee] ... will provide important tools and unique models for a variety of different areas of biology, including social behavior," says Gene E. Robinson, professor of entomology and director of the neuroscience program at University of Illinois at Urbana-Champaign, and lead author of the proposal that the NHGRI reviewed.
Robinson ticks off numerous reasons why the honeybee fits the institute's sequencing requirements: Bees are models for learning and memory; for studies of allergic disease; for gerontology research, as the long-lived, egg-producing queen is genetically identical to the much shorter-lived female workers; for studies of venom toxicology; and for studies of infectious diseases in dense societies. "The basic thrust that underlies everything about the [honeybee] genome is the notion [that], although phylogenetically distant from the human, honeybees live in societies that rival our own in complexity and in success in dealing with the many challenges posed by social life," says Robinson. "They are literally a magic well for discoveries in biology in a huge range of biological disciplines," explains Francis Ratnieks, director of the Laboratory of Apiculture and Social Insects, University of Sheffield, UK. "If you study it, you could be studying practically any topic in biology."
Nicholas Calderone, assistant professor of entomology at Cornell University, points out a practical reason for studying bees: they add $14.5 billion annually to the value of US agriculture. "They're indispensable to modern agriculture and the production of various fruit and vegetable crops," he says.
FOREIGN INVADERS Orley "Chip" Taylor, Jr., a professor in the ecology and evolutionary biology department, University of Kansas, Lawrence, says he is noticing more research in the field, and he believes that the African bee's arrival in the Americas is the cause. This bee is aggressive toward humans and, if able, will take over a European honeybee hive. (The European bees have been here for centuries: early colonists brought them to the Americas.)
African bees are present in a swath that stretches from Texas up into the San Joaquin Valley of California, says research leader Gloria DeGrandi-Hoffman, Agricultural Research Service's Carl Haydon Bee Research Center in Tucson, Ariz. DeGrandi-Hoffman and Stanley Schneider, University of North Carolina, Charlotte, are studying how African bees take over a European hive. "An African colony will send out small swarms of bees, [which] can get into European colonies," says DeGrandi-Hoffman. "Sometimes, those small swarms will have queens in them." If an African queen encounters and kills her European counterpart, then the African bees assume control of the colony, she says. As honeybee colonies are matrilineal, DeGrandi-Hoffman and Schneider are looking at the mitochondrial DNA and nuclear DNA markers to determine what happens genetically when African bees take over. This research can aid the US beekeeping industry, as beekeepers must maintain their hives' genetic integrity in areas where African bees are present.
Although Calderone's group at Cornell is studying the standard areas in agronomy (breeding strains for better honey production and more effective plant pollination), they also are looking at hive organization by examining the homeostatic mechanisms regulating honeybee colonies. "They store about a kilogram of pollen in the hive," explains Calderone. "When they reach that level, they slack off on collecting pollen. When they get very far below that, they increase collecting pollen." How do foragers know how much pollen is in the hive? Researchers report that forager honeybees accomplish this by observing the pollen- containing cells in the hive.1,2
NO SOCIETY IS WITHOUT CONFLICT Insect societies are not immune to conflicts, which, says Sheffield's Ratnieks, are always about reproduction. Although the queen is the chief egg-layer, worker bees, which are females, have ovaries and can lay male-producing haploid eggs. "On the one hand, the individual worker would like to lay eggs," says Ratnieks. But, "the society as a whole doesn't want [them to]." He states that an average Apis mellifera colony raises 100 males daily during spring and summer.3 But, if the colony had its maximum of 60,000 workers, and each was allowed to lay eggs, then more than 100,000 eggs would be produced daily. Such reproduction must be suppressed, and to do this, worker bees police the hive and eat these eggs. Relatedness and shared genes explain this situation, in that worker bees are more related to the queen's sons than to the sons of other workers.3
Ratnieks, too, questions how bees organize themselves. He likens the beehive to a supermarket, with forager bees queued at checkout lines to drop off their nectar. They must "keep a balance on the number of bees working at receiving and the number of bees collecting nectar," he says. If their wait to unload is short, indicating there are few foragers, the forager bee can do a waggle dance to recruit more bees for the quest.
A beehive, says Ratnieks, does not have a manager "who knows what's going on, issuing instructions. Each worker makes her own perceptions." Yet, a hive is highly structured. "You can't de-organize them. If you put 300 to 400 bees in a hive, they start to build a colony," Cornell's Calderone says. "There are a lot of interesting things built into their genetics that ... enable them to do this." His group is working to figure out how bees coordinate their activities and survive.
Bee studies cover more than just social behavior; Brian Smith and colleagues at Ohio State University, Columbus, are studying how bees perceive odors. These odor-decoding mechanisms are analogous in honeybees and in vertebrates, he says. "There are a limited number of ways--perhaps only one or two--that a brain can encode odors and odor memories." He explains that in the vertebrate's brain, the cells in the olfactory bulbs look very similar to cells found within the antennal lobe of the honeybee brain. Smith's work, which is supported by the National Institutes of Health, has basic biomedical applications in understanding olfaction, and in understanding how the honeybee functions in its environment.4
Myrna Watanabe is a freelance writer in Patterson, NY.
1. N.W. Calderone, B.R. Johnson, "The within-nest behaviour of honeybee pollen foragers in colonies with a high or low need for pollen," Animal Behaviour, 63:749-58, April 2002.
2. D.M. Vaughan, N.W. Calderone, "Assessment of pollen stores by foragers in colonies of the honey bee, Apis mellifera L.," Insectes Sociaux, 49:23-7, 2002.
3. F.L.W. Ratnieks, "Worker policing in the honey bee: basic facts and ideas," Insect Social Life, 3:3-10, 2000.
4. G.A. Wright et al., "Ability of honey bee, Apis mellifera, to detect and discriminate odors of varieties of canola flowers (Brassica rapa and Brassica napus) and snapdragon flowers (Antirrhinum majus)," Journal of Chemical Ecology, 28:701-20, April 2002.
©2002, The Scientist Inc.