Task Allocation in Social Animal Colonies

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Gordon 9603639 Like a brain or an embryo, a social insect colony functions without central or hierarchical control. Simple decisions by individual units, the workers, lead to the complex behavior of the colony, though no individual directs the behavior of others. Colonies perform a variety of tasks outside the nest, including foraging, nest maintenance work, and patrolling. As conditions change, the numbers of ants required for each task also change. Task allocation is the process that results in the right numbers of ants performing the right tasks for the current situation. How do colonies accomplish this without central control? Individuals make decisions based on local information. These decisions determine whether an individual will switch tasks, an whether it will pursue a task actively or instead remain inactive inside the nest. The proposed work will investigate what cues ants use in making task decisions. The proposed research explores the possibility that the rate or number of interactions among nestmates is one of the cues involved in tasks allocation decisions. The work will use laboratory colonies of marked individuals, in which all behavior inside the nest is visible, and computer simulations based on a mathematical model of task allocation. Because the rate of encounter among ants depends on how they move around, an image analysis system will be employed to track the paths of ants as they move around the laboratory nest and arena. How ants respond to the rate of brief interactions with other ants, will be examined in undisturbed colonies and in experiments that manipulate worker density, and thus encounter rate. Chemical analysis of the hydrocarbons on the surface of an ant s body will test whether ants engaged in a particular task might carry an odour specific to that task, which other ants could use to distinguish the task of the ants they meet. This research should provide new insight into the ways that fairly simple individ ual behavior can generate the complex behavior of social systems.