LEAF DENSITY AND A TRADE-OFF BETWEEN LOAD-SIZE SELECTION AND RECRUITMENT BEHAVIOR IN THE ANT ATTA-CEPHALOTES

This study considers the interplay between individual load-size select ion and recruitment behavior in the leaf-cutting ant Atta cephalotes. Foraging workers anchor themselves on the leaf edge by their hind legs and pivot around them while cutting arcs from leaves. Since workers n ot only cut leaves but also lay chemical trails to recruit nestmates, we investigated whether there is conflict of motivation affecting the workers' decision either to quickly inform nestmates about a newly dis covered food source, or instead to cut full-load leaf fragments, which could delay recruitment. Workers were presented with leaves of privet of three different grades of toughness (measured as leaf density = ma ss/area) as sources of different quality, and load-size selection and recruitment behavior by harvesting-satiated and harvesting-deprived wo rkers were measured. The following results were obtained. (1) Leaf den sity affected individual load-size selection: both harvesting-satiated and harvesting-deprived workers were found to cut smaller leaf fragme nts from the denser leaves. (2) Harvesting-deprived workers cut smalle r fragments than harvesting-satiated workers, and therefore saved cutt ing time. The fragments cut were smaller only during the initial phase s of the recruitment process, when information about the discovery nee ded to be transferred. (3) Harvesting-deprived workers showed higher r ecruitment rates than harvesting-satiated workers. A considerable numb er of ants were observed to return to the nest unladen. During the ini tial phases, the ratio of laden/unladen workers was lower than that fo r harvesting-satiated workers, and increased with the development of t he foraging process. (4) Scout workers confronted with familiar leaves ran back to the nest laying chemical trails without even contacting t he leaves. They relied on olfactory cues to start recruiting nestmates , and leaf density played no role in their decisions. (5) When confron ted with unfamiliar leaves, on the other hand, they assessed leaf qual ity by probing bites at the leaf edge, although no actual cuts occurre d. In this situation, the resulting recruitment rates depended on phys ical leaf traits, being higher for the tenderer leaves. (6) Workers fo raging on unfamiliar leaves cut smaller fragments than workers cutting familiar leaves, and most of them displayed trail-laying behavior whe n returning to the nest. The results support the hypothesis of a trade -off between time spent collecting and that invested to recruit nestma tes. During the initial phases of exploitation of a newly discovered f ood source, workers reduced their individual carrying performance in o rder to return earlier to the colony for further recruitment.