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J Insect Behav (2009) 22:217226
DOI 10.1007/s10905-008-9167-7
Jan Oettler & Robert A. Johnson
Revised: 22 April 2008 /Accepted: 12 October 2008 /
Published online: 31 October 2008# Springer Science + Business Media, LLC 2008
Abstract We examined temporal polyethism in Pogonomyrmex rugosus, predicting a pattern of decreasing age from foragers to nest maintenance workers to individuals that were recruited to harvest a temporary food source. Nest maintenance workers were younger than foragers, as indicated by their heavier mass and lower mandibular wear. In contrast, recruited foragers were similar in mass to foragers but they displayed higher mandibular wear, suggesting that they were at least as old as foragers. Longevity estimates for marked individuals of these two latter task groups showed mixed results. Higher mandibular wear of recruited foragers suggests that they did not follow the normal sequence for temporal polyethism, but rather that they functioned as seed-millers, which should more quickly abrade their dentition. This would be the first demonstration of specialist milling individuals in a monomorphic seed-harvester ant.
Keywords Age polyethism . forager . Pogonomyrmex rugosus . nest maintenance workers . recruited foragers
Introduction
Division of labor is considered to be one of the cornerstones for the phenomenal success of social insects (Traniello and Rosengaus 1997). Such division of labor
J. Oettler
Institut fr Zoologie und Anthropologie, Georg-August-Universitt Gttingen, 37073 Gttingen, Germany
R. A. Johnson
School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
Present address:J. Oettler (*)
Biologie 1, Universitt Regensburg, 93040 Regensburg, Germany e-mail: [email protected]
The Old Ladies of the Seed Harvester ant Pogonomyrmex Rugosus: Foraging Performed by Two Groups of Workers
218 J Insect Behav (2009) 22:217226
occurs via morphological differences among individuals within a colony (size polyphenism or castes) or via temporal polyethism, which involves age-related changes in tasks performed by workers independent of variation in size. Division of labor via morphological castes is uncommon given the low percentage of social insects that exhibit substantial size variation or physical castes (Wilson 1953; Hlldobler and Wilson 1990). Alternatively, temporal polyethism is common among social insects, and is best studied in honey bees (Seeley 1982; Seeley and Kolmes 1991; Robinson 1992).
In general, temporal polyethism follows the pattern of young workers performing inside the nest tasks while older workers perform...