Task-Related Differences in the Cuticular Hydrocarbon Composition of Harvester Ants, Pogonomyrmex barbatus

Abstract

Colonies of the harvester ant, Pogonomyrmex barbatus, perform a variety of tasks. The behavior of an individual worker appears to depend on its recent history of brief contacts with ants of the same and other task groups. The purpose of this study was to determine whether task groups differ in cuticular hydrocarbon composition. We compared the cuticular hydrocarbon composition of ants collected under natural conditions as they performed one of three tasks: patrolling (locating food sources), foraging, or nest maintenance. Task groups differed significantly in the relative proportions of classes of hydrocarbon compounds, as well as in individual compounds. Relative to nest maintenance workers, foragers and patrollers had a higher proportion of straight-chain alkanes relative to monomethylalkanes, dimethylalkanes, and alkenes. There was no significant difference in the chain length of n-alkanes among the task groups. Foragers did not differ in hydrocarbon composition from patrollers. Colonies differed significantly from one another in hydrocarbon composition, but task groups differed in consistent ways from colony to colony, suggesting that the mechanism responsible for task-related hydrocarbon composition was the same in all colonies. P. barbatus workers switch tasks during their lifetimes, suggesting that cuticular hydrocarbon composition changes during adulthood as well. Nest maintenance workers are probably younger than foragers and patrollers and perform very little of their work outside of the nest. Task-related hydrocarbon differences detected here may be associated with worker age, and/or the abiotic characteristics (temperature, humidity, and ultraviolet light) of the interior and exterior work environments.