Researchers sweeten the pot of honeybee knowledge
Deborah Smith, associate professor of ecology and evolutionary biology, has studied the genetics and biogeography of honeybees for more than 20 years.
Now her research is part of a team effort to learn how honeybees achieved their far-flung distribution, how Africanized bees spread in the Americas and how a queen bee produces offspring.
Recently, the Honeybee Genome Sequencing Consortium, a swarm of researchers from around the world, presented the complete DNA sequence of the genome of Apis mellifera, the honeybee. Multiple research papers accompanied the release of the genome sequence.
One of those papers, "Thrice out of Africa: Ancient and modern expansions of the honey bee, Apis mellifera," was published in the journal Science.
"For more than 100 years, scientists and bee keepers have studied honeybees and noticed geographic variation in how they forage, what flowers they use, what diseases they are susceptible to or how gentle they are," Smith said.
Smith says until now, researchers didn't have the tools to determine if these regional populations were genetically distinct or how populations were related to each other.
But now, the Honey Bee Genome Project, funded by the National Human Genome Research Institute and the U.S. Department of Agriculture, gives thousands of genetic markers to examine.
Smith and Orley "Chip" Taylor, professor of ecology and evolutionary biology, collected bees from Europe, Africa, the Middle East and South Africa.
Comparing parts of the chromosomes of European and African bees revealed places where the bees' genetic sequences differed by one base. These sequences are called single nucleotide polymorphisms or SNPs.
The SNPs showed that there are four main genetic lineages of honeybees: west European, east European, Middle Eastern, or Oriental, and African. They also suggested that the bees originated in Africa and spread from there into Europe, the Middle East and Asia Minor.
Smith and the HBG consortium also investigated the genetic composition of Africanized bees and European bees in the Americas.
"North American beekeepers love to have pedigreed bees," she said. "But when we looked at the background of European bees of North America, they all showed mixed ancestry, from eastern and western Europe and from the Middle East."
Another project investigated sex determination in Asian honeybees.
The paper, "Evolution of the Complementary Sex-Determination Gene of Honey Bees: Balancing Selection and Trans Species Polymorphisms," was published in a special honeybee issue of Genome Research.
A gene called the complementary sex-determination gene determines the gender of a honeybee. Normal female honeybees have two copies of the gene, one from each parent. Normal male honeybees have only one, because they develop from unfertilized eggs. But if a queen bee mates with a male carrying the same form of csd, some of those young will have two identical copies and will develop into abnormal males.
Smith says other worker bees in the colony detect these abnormal males and eat them just after they hatch. This could lead to a shortage of female worker bees in the colony and put a premium on variety and diversity in the forms of csd found in a population. If there is more variety, there is less chance of producing the abnormal males.
In the Genome Research article, Smith and her colleagues determined that the csd gene is seven times more likely than neutral regions of the honeybee genome to exist in several forms, and that some variations of csd are kept in populations for a long time. Some csd variants appear to have originated in the common ancestor of today's species of honeybees.
"The association between humans and honeybees goes back to prehistoric times. We hunt them for honey, raise them for honey and pollination services, and marvel at their communication and social behavior," Smith said.
"Now we have tools to really address questions about the genetic basis of sociality, aggression, development, sex determination and so many other aspects of their biology."
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