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.