ANN ARBOR, Mich.---What makes a bee a he or a she?
Three years ago, scientists pinpointed a gene called csd that determines gender in honey bees, and now a research team led by University of Michigan evolutionary biologist Jianzhi "George" Zhang has unraveled details of how the gene evolved. The new insights could prove useful in designing strategies for breeding honey bees, which are major pollinators of economically important crops---and notoriously tricky to breed.
The findings of Zhang and collaborators appear in a special issue of Genome Research devoted to the biology of the honey bee. The issue will be published online and in print Oct. 26, coinciding with the publication of the honey bee genome sequence in the journal Nature.
Scientists have long known that in bees---as well as wasps, ants, ticks, mites and some 20 percent of all animals---unfertilized eggs develop into males, while females typically result from fertilized eggs. But that's not the whole story, and the discovery in 2003 of csd (the complementary sex determination gene) helped fill in the blanks. The gene has many versions, or alleles. Males inherit a single copy of the gene; bees that inherit two copies, each a different version, become female. Bees that have the misfortune of inheriting two identical copies of csd develop into sterile males but are quickly eaten at the larval stage by female worker bees.
The system works fine in nature, where it prevents the colony from wasting precious energy and resources on abnormal males incapable of carrying out the all-important role of mating. But in bees raised for honey or for pollinating crops, the sex-determination system can cause problems. Beekeepers inbreed bees to select desirable traits, but inbreeding raises the odds of producing fertilized eggs with two copies of the same csd allele. If too many sterile males result, the colony may die out.