--by Margaret Coulombe

Paper wasps are primitive social insects. But when a paper wasp larvae slips into the quiet pupal stage, she doesn’t know if she’ll arise a worker or gyne (a future queen). Unless, of course, she consults with Arizona State University’s social insect researcher Gro Amdam.

By studying this primitive social order of wasps, Amdam’s group is shedding new light on the development of colonial insects from solitary ancestors. Scientists know paper wasps as Polistes metricus. The scientists learned that paper wasp larvae that can become future queens show signs of developmental diapause. This period of overt inactivity is a life history trait found in many insect orders.

Can the larval environment really determine future royal stature? The concept of environmental cues, things like weather, shorter day length, or food availability, determining destiny seems distinctly foreign in humans.

Amdam is an associate professor in ASU’s School of Life Sciences. She has pioneered a new understanding of the developmental programs underlying diapause and reproduction. Amdam says they can be adopted in primitively social settings to result in the complex social behaviors and castes found in advanced insect societies.

The biology and physiology of the Polistes wasp is more "transparent," she says. It is not highly derived as is often the case of highly social insects, such as honeybees. As a result, scientists can more easily backtrack.

“We can follow the footprints of evolution and uncover the pathways that castes originally evolved from,” says Amdam.

Many species of highly social insects have two distinct female castes, workers and queens. The traits are set in larval life. However, Amdam points out that the primitive social Polistes wasp was originally believed to lack developmental castes entirely. It was thought to be more like its solitary ancestors.

Individual females were thought to simply “choose” to become workers or queens—as adults. Previous work by Amdam and colleagues suggested otherwise. They had the idea that a bias toward “queen-ness” might occur earlier in life than previously believed. And that bias might be tied to diapause, an old life history trait found in both solitary and social insects.

The scientists found hard evidence for their ideas in the form of a storage protein called hexamerin. Specifically, they found that the levels of hexamerin differed in paper wasp larvae and pupae destined to become workers or gynes.

Amdam says the group’s work challenges the view that workers and gynes represent behavior options equally available to every female offspring. “The findings exemplify how social insect castes can evolve from casteless lineages,” she says.

Read a longer version of this story at SOLS News: http://sols.asu.edu/sols_news/43_news_07.php

For more details about the research, see the groups’ paper published in the August 28, 2007 edition of the Proceedings of the National Academy of Sciences (PNAS).