Use of Multiple Cues for Navigation by the Leaf-cutter Ant Atta cephalotes.
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In the first chapter, there is a brief introduction to ant navigation and a review of previous literature as well as a summary chapters 2-7. In chapter 2, I examine orientation of Atta cephalotes workers in the laboratory. Laden nest-bound foragers were moved from a "bridge" with or without trail pheromone present and placed on a parallel bridge with or without pheromone. In chapter 3, I continue to examine orientation of A. cephalotes foragers in the laboratory. Foragers walked on a single bridge and I altered various cues and contexts and recorded which manipulations caused the ants to reverse course. In chapter 4, I put orientation cues into direct conflict by letting the ants forage on a Y-maze. Foragers that were returning to a food source preferred visual cues to odor cues while recruited foragers consistently used odor cues. In chapter 5, I use a vertical T-maze to investigate the role that gravity plays in A. cephalotes navigation. The gravitational cue was put in direct conflict with odor cues and light cues. There was an asymmetry to the ants' response to the gravity cue in that ants returning to a food source had a tendency to go up regardless of the previous position of the food source or the position of the odor trail. Introducing a light cue changed the angle required to make the ants respond to the gravitational cue. In chapter 6, I investigate the anatomy of A. cephalotes eyes and brains. Based on tissue sections, I measured the angles between adjacent ommatidia in the eyes, and the volumes of sub-compartments of the brain. In chapter 7, I use the results from the other chapters to inform my speculations about the nature and neural basis of A. cephalotes navigation. I develop an hypothesis of navigation in the wild and a simple model of its neural underpinnings.