Trunk trail maintenance in leafcutter ants: caste involvement and effects of obstacle type and size on path clearing in Atta cephalotes

Abstract

Morphological castes occur throughout ant species, but their role in task partitioning and colony success remains controversial. Task partitioning based on size is thought to increase colony efficiency, but tests of this hypothesis are difficult. In this study, we delve into the role of different morphological castes of Atta cephalotes in the maintenance of trunk trails, a task considered very important to foraging efficiency in leafcutters. Using differently sized dead and live leaves as obstacles, we tested for evidence of size matching by performing sixty trials in which we recorded the involvement of different castes and the effect of removal of majors on obstacle removal in one A. cephalotes colony. Ants treated live and dead leaves in the path identically. Cutting and pulling of larger leaves involved more ants (of all size castes), and took longer. Removal of the majors (22% of all workers involved) did not negatively impact removal time of obstacles of any size. We hypothesized that there would be matching between ant size and the size of the obstacle removed, but we found no evidence for such matching. Mediae were more likely to pull than minors. When the majors were removed, the minors and mediae increased in cutting and pulling leaves to compensate, with the mediae particularly increasing in pulling. Overall, our results suggest that minors and mediae differ in task partitioning for obstacle removal, and that castes can respond flexibly to removal of other castes. However, we found no evidence that morphological castes improve capacities for trail clearing.