For social insects — like bees, ants and termites — differences in looks and behavior are easy to see. Some become soldiers or workers while others turn into egg-laying queens, even though a colony is comprised of nearly genetically identical individuals.

What determines the fate of a given offspring? For at least one wasp species, it’s the germ cells — stem cells that give rise to eggs and sperm.

University of Georgia entomologist Michael Strand and his collaborators studied a parasitic wasp (Copidosoma floridanum) that produces roughly 2,000 identical sibling wasps from a single egg. Even though each wasp in a colony is genetically identical, individuals develop into two distinctly different castes: soldiers and queens.

The reason is that germ cells are parceled out to some embryos and not to others. The embryos that inherit the germ cells also inherit “the throne,” while those that missed out must serve to protect it.

This is a previously unknown role for germ cells in development, Strand said.

“These results indicate that germ cells not only are important for gamete egg and sperm formation but also influence how individuals look and behave,” he said.

Future studies of this wasp may help uncover the mechanism that controls whether a germ cell divides or not.

“Germ cells are formed very early in the embryogenesis of wasps, long before any individuals develop into a soldier or queen,” Strand said.

In humans and other animals, germ cells also form early in developing embryos but they then become dormant until the animal reaches reproductive maturity. Dormancy is believed to protect cells from genetic errors that can occur during cell division.

In contrast, this wasp’s germ cells avoid dormancy and proliferate.

Since “the molecular toolbox” regulating germ cell formation is likely similar for all animals, this wasp may help scientists understand the “cell division braking” mechanism in most germ cells, Strand said.

These finding were published in the July 6, 2004, issue of the Proceedings of the National Academy of Sciences and the August 5, 2004, issue of Nature.