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From the Cover
BIOLOGICAL SCIENCES / EVOLUTION
A diapause pathway underlies the gyne phenotype in Polistes wasps, revealing an evolutionary route to caste-containing insect societies

James H. Hunt^*,, Bart J. Kensinger^*, Jessica A. Kossuth^*, Michael T. Henshaw, Kari Norberg, Florian Wolschin^¶, and Gro V. Amdam^,,¶

*Department of Biology, University of Missouri, St. Louis, MO 63121; Division of Science and Math, McKendree College, Lebanon, IL 62254; Department of Animal and Aquacultural Sciences, University of Life Sciences, Aas N-1432, Norway; and ^¶School of Life Sciences, Arizona State University, Tempe, AZ 85287

Communicated by Edward O. Wilson, Harvard University, Cambridge, MA, July 16, 2007 (received for review February 5, 2007)

Colonies of social wasps, ants, and bees are characterized by the production of two phenotypes of female offspring, workers that remain at their natal nest and nonworkers that are potential colony reproductives of the next generation. The phenotype difference includes morphology and is fixed during larval development in ants, honey bees, and some social wasps, all of which represent an advanced state of sociality. Paper wasps (Polistes) lack morphological castes and are thought to more closely resemble an ancestral state of sociality wherein the phenotype difference between workers and nonworkers is established only during adult life. We address an alternative hypothesis: a bias toward the potential reproductive (gyne) phenotype among Polistes female offspring occurs during larval development and is based on a facultatively expressed ancestral life history trait: diapause. We show that two signatures of diapause (extended maturation time and enhanced synthesis and sequestration of a hexameric storage protein) characterize the development of gyne offspring in Polistes metricus. Hexameric storage proteins are implicated in silencing juvenile hormone signaling, which is a prerequisite for diapause. Diverging hexamerin protein dynamics driven by changes in larval provisioning levels thereby provide one possible mechanism that can cause an adaptive shift in phenotype bias during the Polistes colony cycle. This ontogenetic basis for alternative female phenotypes in Polistes challenges the view that workers and gynes represent behavior options equally available to every female offspring, and it exemplifies how social insect castes can evolve from casteless lineages.

caste development | hexameric storage proteins | juvenile hormone | life-history pleiotropy | social behavior

The authors declare no conflict of interest.

This article contains supporting information online at www.pnas.org/cgi/content/full/0705660104/DC1.

To whom correspondence should be addressed. E-mail: jimhunt{at}umsl.edu or gro.amdam{at}asu.edu

© 2007 by The National Academy of Sciences of the USA

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PNAS 2007 104: 13853-13854. [Full Text]