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Honeybee Genome Sheds Light on "Killer" History, Bee Secrets

Anne Minard
for National Geographic News
October 25, 2006
 
Scientists have sequenced the honeybee genome, revealing some of the biology beneath the insects' advanced social systems and powerful sense of smell as well as the spread of Africanized (or "killer") strains.

The study, which paves the way for a new era of bee research, marks the third insect genome to be sequenced, after the fruit fly and the mosquito.

Scientists have long wanted to know what makes the honeybee—Apis mellifera—tick, because it serves as a model for social behavior and because of its vital worldwide role as a pollinator (honeybee photos, facts, and more.

Honeybees form elaborate hives and divide into complex social strata, and some honeybees have even learned abstract concepts such as "same" and "different" in the lab.

But honeybee brains contain only a million neurons. That's a hundred thousand times fewer cells than human brains and only four times more than a fruit fly's.

The new genome research doesn't disappoint.

"I don't want to go so far as to say it's done a better job of evolving," said Kim Worley, a researcher at Baylor College of Medicine in Houston, Texas, and one of the study co-authors. "The honeybees have got a lot of interesting biology, and we're seeing genes that can explain some of it."

A paper summarizing the research, which was led by George M. Weinstock, also at Baylor College of Medicine, will appear in tomorrow's issue of the journal Nature.

Understanding a "Killer"

The genome data sheds light on the process of Africanization by suggesting that Apis mellifera originated in Africa, then spread to Europe and Asia in two separate migrations. (Related: photo: "Oldest-Ever Bee Found in Amber" [October 25, 2006].)

The infamous African "killer" bees, a subspecies of honeybee known as Apis mellifera scutellata, were introduced to Brazil in 1956. The aggressive insects have almost replaced the so-called European honeybees that were present in the region and have penetrated as far as Argentina to the south and California to the north.

The new study also reveals how elements in the genome may influence the development of vastly different honeybee castes, such as queens and workers, from the same genetic material.

There is typically one queen per colony, but she can live for up to two years (ten times as long as workers), can lay 2,000 eggs a day, and can store sperm for years without it losing viability.

Skilled, sterile workers number tens of thousands per colony. They can learn to associate a flower's color, shape, scent, or location with a food reward, then communicate new food discoveries to the hive using "dance language."

A Different Kind of Bug

The researchers also found a number of differences between honeybee genes and those of the other insects.

The honeybee genome, for instance, has evolved more slowly over time. And honeybees have fewer genes for taste than for smell, which may explain their exceptional ability to find pollen-rich flowers.

Honeybees also have fewer genes providing resistance to disease than the other insects. That's counterintuitive, Worley says, because honeybees live communally and are probably exposed to quite a few pathogens.

Worley suggests that the bees' highly evolved sociality—including their quickness to cast out sick members of the hive, their social grooming behaviors, and their use of separate chambers to raise young—may have developed as an alternate defense.

"Their immune systems may have evolved [to counter specific threats], and so they're highly tuned to deal with co-evolved pathogens," she said. "The other hypothesis is that we just don't know."

The size of the major gene families responsible for detoxification also appears smaller in the honeybee, making the species unusually sensitive to certain pesticides.

In addition, the bee genome is more similar to vertebrate genomes in regions that influence circadian (24-hour) rhythms.

"It's intriguing ... to wonder about what those genes are doing and how that affects the honeybee," Worley said.

Going, Going, Gone?

The honeybee genome research comes on the heels of a report, "Status of Pollinators in North America," commissioned by the National Academy of Sciences and released last week.

The paper sent out dire warnings about declines and even extinctions of pollinator species worldwide. (Related: "Buzz Kill: Wild Bees and Flowers Disappearing, Study Says" [July 21, 2006].)

According to Stephen Buchmann, an associate professor of entomology at the University of Arizona in Tucson and one of 15 members of the report committee, "our best defense against crop failures, yield shortfalls, and so-called pollinator crises is to have wild bees and managed non-Apis pollinators as part of a balanced pollinator portfolio for the world's wild and cultivated plants."

Baylor's Worley says further work with the honeybee genome will occur on several fronts.

The public may be most interested in the spread of Africanized bees, she says, but beekeepers are likely to also be concerned about the decline of pollinators.

"I think there's a lot of fodder for all of those research efforts," she said. "Any genome moves things ahead rapidly."

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