By Cat Holmes
University of Georgia
Anyone who’s ever watched an ant farm or beehive knows that
some insects are social creatures.
In fact, “a lot of insects are social,” said University of
Georgia entomologist Michael Strand. “They’ve evolved societies
in which different individuals have different functions.
They’ve also evolved completely different body shapes and
behaviors.”
That means that, despite the fact that they begin with
essentially the same genetic material, some individuals develop
into queens that reproduce while others develop into soldiers
or workers that defend and maintain the colony.
This ability for something with the same genetic material to
look and behave differently is called phenotypic plasticity.
Examples of phenotypic plasticity are also known to occur in
many other animals, yet scientists do not understand very well
how this occurs at a cellular or molecular level.
However, recent UGA studies have shed new light on this
question by finding that caste formation in a unique type of
wasp is strongly influenced by whether individuals possess a
specialized type of cells called germ cells.
The study, published in the July 6 issue of the Proceedings of
the National Academy of Sciences, also reveals a previously
unknown role for germ cells in development according to Strand,
one of
the authors of the study.
Doubl[ing] agents
The wasp used in the study is “a particularly elegant model
[for this research] because its eggs develop clonally to
produce genetically identical offspring,” Strand said.
So, in much the same way human identical twins are formed from
one egg, each egg laid by this wasp produces roughly 2,000
identical sibling wasps.
Yet despite each wasp in a colony being genetically identical,
individuals develop into two distinctly different castes:
soldiers and queens.
The question addressed in the UGA study was what determines at
a cellular and molecular level whether a given offspring
develops into a queen or soldier. The answer is germ cells.
Germ cells
Germs cells are determined very early in the development of
mammals as well as insects.
“Germs cells are formed very early in the embryogenesis of
wasps, long before any individuals develop into a soldier or
queen,” Strand said.
In humans as well as insects, the main function of germ cells
is to give rise to reproductive cells (sperm and eggs) that
will produce offspring in the next generation. Germ cells
usually remain dormant in humans and other animals until they
reach maturity and are able to reproduce.
In the wasps used in this study, however, germ cells were
parceled out to some embryos and not others. The embryos that
inherited germ cells went on to develop into queens, while
embryos without germ cells developed into soldiers.
“These results indicate that germ cells are not only important
for gamete formation but also influence how individuals look
and behave,” Strand said.
The next step for the UGA research team will be to uncover how
germ cells modulate the activity of other cells and genes that
regulate growth, development and behavior.
The full text of this study can be found at the PNAS Web site:
www.pnas.org/cgi/content/abract/101/27/10095
(Cat Holmes is a news editor with the University of Georgia
College of Agricultural and Environmental Sciences.)
