Michigan State researcher traces the evolution of honey bee gender
EAST LANSING, Mich. -- A first-of-its-kind evolutionary strategy discovered among invertebrate organisms – or honey bees – shows how a complex genetic mechanism determines gender and maximizes gene transmission to the next generation of several bee species, according to Michigan State University researchers.
The research of Zachary Huang, MSU associate professor in the Department of Entomology, and his colleagues will be featured in the Oct. 26 edition of the journal Genome Research.
"This research gives us a better understanding of the sex-determining system of honey bees, as well as the age and evolutionary history of the csd (complementary sex determination) gene," Huang said. "The various versions of the csd genes are shared among honey bees. They evolved before they became different species."
In addition, the findings also will allow breeders to design better and more efficient mating systems. Breeders more easily will be able to raise new queens to lead hives.
This research is supported by grants from the National Institutes of Health, Office of Vice President for Research of the University of Michigan, the University of Kansas General Research Fund and the Michigan Agricultural Experiment Station.
The csd gene determines the difference between a male and female honey bee, according to Huang. His research shows this method of sex determination first appeared in a shared ancestor of the European and three Asian honey bee species.
In humans, sex is determined by the combination of sex-determining chromosomes one has. In females, both sex-determining chromosomes are the same – XX; for males the two chromosomes are different – XY.
Honey bees do things a bit differently. Specific combinations of the csd gene regulate the gender and social roles of each honey bee.
In the past, scientists thought the sex determination of offspring was left purely up to the queen, Huang said. Scientists believed that after a queen bee returned to her hive from a mating flight she had a choice of laying fertilized or unfertilized eggs. The unfertilized eggs would develop into male drones. The fertilized eggs develop into female honey bees. But there's more to the story.
Alleles are different versions of the same gene. In humans, they dictate characteristics like eye and hair color.
If the bee has two different alleles, the csd gene will be female. If it has only a single version of the gene, it will become a normal, fertile male. Finally, if the bee has two identical csd types it will become a diploid male, which is infertile, Huang explained. The unlucky infertile males will never successfully reproduce so they are eaten by other members of the hive to save resources.
Aside from determining life and death, csd mechanism is important to the overall function of the hive.
There's a big difference between the duties of a fertile male honey bee and those of a female. The males lead a life of luxury – their duties include eating, resting and mating.
After hatching a female's life can take one of two directions. Fed a diet of royal jelly, the female hatchling will develop into a queen bee. If not, she will become one of the 20,000 to 60,000 worker bees tending to the needs of the hive, the drones, her queen and the next generation.
Ultimately the csd system shared by all honey bee species means increased genetic diversity and a better chance for their genes to carry over to the next generation.
"This is a matter of gene transmission," Huang said. "It is an evolutionary strategy to maximize gene transmission to the next generation."
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