Sequential Load Transport in Grass-Cutting Ants (Atta vollenweideri): Maximization of Plant Delivery Rate or Improved Information Transfer?

Sequential transport of plant fragments was studied in the grass-cutting ant Atta vollenweideri. Two competing hypotheses concerning its occurrence were tested. Based on the “economic-transport hypothesis," sequential transport occurs because of a mismatch between load size and ant body size, and it is therefore considered a way to improve size-matching and so the plant delivery rate. Alternatively, the “information-transfer hypothesis" states that sequential transport improves the information flow during foraging. By transferring its load, a worker may return earlier to the foraging site so as to intensifychemical recruitment. To distinguish between these two competing hypotheses, standardized paper fragments that differed either insize or in quality were presented to workers of a field colony, and sequential transport was quantified. Neither an increase infragment mass nor in fragment length influenced the occurrence of transport chains. Sequential transport took longer than transportby a single carrier. However, the occurrence of sequential transport increased with increasing fragment quality. High-qualityfragments were transferred more frequently and after shorter distances than less-attractive fragments. Taken together, theseresults strongly support the hypothesis that sequential load transport has been favoured during evolution because of animprovement in the information flow during foraging