Abstract
In the Florida harvester ant, Pogonomyrmex badius, foragers occur only in the top 15 cm of the nest, whereas brood and brood-care workers reside mostly in the deepest regions, yet the food and seeds foragers collect must be transported downward 30 to 80 cm to seed chambers and up to 2 m to brood chambers. Using mark-recapture techniques with fluorescent printer's ink, we identified a class of workers that ranges widely within the vertical structure of the nest, rapidly moving materials dropped by foragers in the upper regions downward, and excavated soil from deeper upward. Within the nest, only 5% of foragers were recovered below 20 cm depth, but about 30% of transfer workers and 82% of unmarked workers were found there. Below 70 cm depth, 90% of workers were unmarked, and were probably involved mostly in brood care. During the summer, the transfer workers comprise about a quarter of the nest population, while foragers make up about 40%. Workers marked as transfer workers later appear as foragers, while those marked as foragers die and disappear from the foraging population, suggesting that transfer workers are younger, and age into foraging. The importance of these findings for laboratory studies of division of labor are discussed. The efficient allocation of labor is a key component of superorganismal fitness.
Highlights
Division of labor is a hallmark of insect sociality, and is expressed along multiple axes
Young workers are associated with brood care, moving to more general nest tasks as they age, and becoming foragers outside the nest in old age
We present evidence that such a distinct class of transfer workers operates in the Florida harvester ant, P. badius, and that its operation is associated with worker age and location
Summary
Division of labor is a hallmark of insect sociality, and is expressed along multiple axes. The defining division is between reproductive (queen) and non-reproductive (worker) individuals, but specialization within each of these castes occurs. Division of labor is almost universally associated with worker age (age polyethism), and in those species with highly size-variable workers, with body size. Young workers are associated with brood care, moving to more general nest tasks as they age, and becoming foragers outside the nest in old age. These functional transitions have been described in dozens of species of ants (for more recent examples: [5,6]).
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