An international consortium of researchers announced this week that it has finished sequencing the entire genome — all the DNA — of the honey bee. Washington State University entomologist Walter S. (Steve) Sheppard, a member of the sequencing team, also co-authored a study that strongly suggests that honey bees originated in Africa and spread to Europe and Asia during at least two major migratory periods during their history.
The honey bee genome results appear in this week’s issue of the journal Nature, and the report on honey bee origins appears in this week’s issue of Science magazine.
The honey bee, Apis mellifera, is only the fourth species of insect to have its entire genome sequenced. The others are the silkworm, the mosquito that transmits the malaria parasite and the fruit fly on which a large proportion of genetics research depends.
Sheppard said honey bees are one of the most economically important insects in the world. While well-known for honey production, it is their role as pollinators of crop plants that makes them so valuable to agriculture. The genome sequence provides a vast amount of information that will further our understanding of honey bee behavior and the potential impact of “intruder”
bees such as the Africanized bees that have moved into parts of Texas and the American southwest over the last decade, he said.
“It’s a huge amount of data, and the statistical basis for how to analyze it is in the developmental stages,” said Sheppard.
Working with colleagues from universities across the U.S., Sheppard helped develop new techniques for tracing honey bee relationships by analyzing SNPs (“snips”), or single-nucleotide polymorphisms, within the DNA of honey bees from different regions. A SNP is a change in one letter of the DNA code that occurs in less than 1 percent of the bees examined. By looking at more than 1000 SNPs in the DNA of each of hundreds of individual bees, the researchers were able to develop a distinctive DNA profile for bees from each region.
Sheppard said the traditional view of honey bee origins held that they first arose in western Asia, the area comprising current-day Turkey, Afghanistan, Kazakhstan and Kyrgyzistan, and migrated from there to Europe and Africa.
Among the surprising results of the new analysis was that the type of honey bee common to northern and western Europe is more closely related to modern-day African honey bees than to its geographical neighbors in central Europe. Such discoveries led the researchers to conclude that honey bees probably originated in Africa and migrated into Asia and Europe on at least two different occasions.
After hundreds of thousands of years in their new homes, with no interbreeding among the populations in different areas, they evolved into today’s subspecies whose DNA is unique enough that the SNP analysis can tell to which group they belong.
The researchers also examined honey bees captured at various sites in the U.S. They found that the SNP analysis could track the invasion of “Africanized” bees, which have both European and African subspecies in their pedigree.
All honey bees in the Americas are relative newcomers, Sheppard said. Human settlers first brought western European subspecies in 1622. A Mediterranean subspecies was imported in the mid-1800s, and an African subspecies was brought to Brazil in 1956. Sheppard said the African bees are well-suited to the wet-dry seasonality of Brazil and have one big advantage over European honey bees: they are resistant to a mite that decimates bee colonies and necessitates the use by beekeepers of chemical miticides. It is descendents of the Brazilian-African imports that have recently gained notoriety as fierce defenders of their hives.
“It’s not the stinging behavior that bothers beekeepers,” said Sheppard. “The problem is that in warm places they swarm a lot.” This behavior makes them less suited for the honey production and pollination practices currently being used in the U.S. He said their swarming behavior, when a large colony breaks into multiple colonies, may be the main reason they have not spread farther north in the U.S. The new, smaller colonies are often too small to survive a cold winter.
