USA Biology Olympiad (USABO) Practice Exam

In an ant colony, what does a chemical characteristic of dead ants signify?

1. Food source

2. Sign stimulus for a fixed action pattern

3. Communication of danger

4. Territory marking

The correct answer is: Sign stimulus for a fixed action pattern

The correct answer pertains to the role of chemical signals, known as pheromones, that are released by dead ants. When ants die, they often emit specific chemical compounds that serve as a sign stimulus, alerting other colony members to their presence. This prompts a fixed action pattern among the ants, which is a predictable behavior triggered by the stimulus. The other options, while relevant in different contexts, do not accurately describe the primary function of the chemicals released by deceased ants. For example, while ants may eventually consume dead bodies as a food source, this is not the primary signaling function of the chemicals. Similarly, communication of danger typically involves alarm pheromones that are distinct from those released by dead ants. Lastly, territory marking is accomplished through a different set of pheromones that indicate boundaries rather than signals related to dead colony members. Thus, the role of chemical characteristics in signaling the presence of dead ants is most accurately defined as a sign stimulus for a fixed action pattern among the living ants in the colony.