Public Release: 

Study Examines How Mechanisms Evolve To Regulate Bee Development

University of Illinois at Urbana-Champaign

CHAMPAIGN, Ill. -- With a little hormone jump start from researchers, male honey bees, known as drones, whose only job is having sex, get to work early. The hormonal mechanism, researchers say, has a genetic basis, because the drone sons of fast worker bees inherit accelerated development.

The findings shed evolutionary light on the mechanisms that regulate behavioral development in the drones' sisters, the worker bees, which pollinate almost $15 billion of agricultural crops annually, said Gene Robinson, a professor of entomology at the University of Illinois.

The research, which involved a series of experiments using honey bees (Apis mellifera), was published Oct. 15 in the Proceedings of the National Academy of Sciences. Co-authors were Robinson, an internationally recognized honey-bee expert, and Tugrul Giray, a doctoral student at the U. of I. in entomology.

Honey-bee scientists have a general understanding of how the level of juvenile hormone affects the well-known division of labor among worker honey bees, which plays a key role in the ecological success of the species.

This project, however, looked specifically at how juvenile hormone affects the behavior of the stockier, bigger-winged drones in an attempt to gain insight into the evolution of the mechanisms involved in the division of labor. While drones do not participate in the division of labor, they do undergo a unique pattern of behavioral development in which they grow up and mate.

The same endocrine and genetic mechanisms involved in behavioral development of worker bees -- who tend the hive and, when older, forage -- exist in the drones, researchers found. When the hormone level was elevated, drones began to seek virgin queens earlier than same-aged drones whose levels were not altered. The higher hormone levels, in effect, caused the drones to grow up faster. This is similar to what happens in workers; hormone treatment causes them to start foraging at a younger age.

To test for genetic effects, the researchers created a population without a queen, whose job is to mate and lay eggs. As a result, the workers laid eggs. But because workers don't mate, their eggs go unfertilized and their offspring are drones. Sons of fast workers again grew up fast, suggesting, Robinson said, that drones and workers have similar control mechanisms in their brains, even though their functions in bee society are totally different.

The work, funded by the National Institute of Mental Health and the U.S. Department of Agriculture, could lead to new tools for brain research, Robinson said. "Drones offer an interesting genetic model because they are haploid [having half the number of chromosomes of workers]. With such simplicity, it may be possible to develop molecular genetic tools for analyzing underlying brain mechanisms involved in behavioral changes that could be applied to more complex genetic systems."

For the drones themselves, early maturity brings mixed returns: They can begin looking for a mate earlier, but drones that mate earlier in life die earlier.

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