Pheromone deposition in L. niger
The ant Lasius niger deposits trail pheromone in order to bring nestmates to valuable resources, such as food. The better the food - specifically, the more valuable the ant perceives the food to be - the more likely she is to deposit pheromone.
Pheromone deposition is easily seen - the ant pauses briefly, and presses her abdomen onto the ground.
Value perception in invertebrates
Reference points affect perceived value:
Prospect Theory in ants
Traditional economic theory assumed that the value of something depends soley on what it is worth on the market. However, humans don't work that way. We assign value to a good depending on many things. Importantly, value is perceived in terms of gains and losses from an expected reference point. This insight is encapsulated by Prospect Theory. Our data shows that ants perceive value in the same way.
Methods - how do we do this?
We use a simple method to test value perception in ants - for a step-by-step guide, see this powerpoint presentation. In brief, we allow an ant to find some food of either high quality (very sweet), low quality (slightly sweet) or somewhere in between. The ant runs back to the nest, unloads, then comes back for more. This time, however, she always finds a medium-quality food. Once she drinks she runs back to the nest again, and we record the number of pheromone dots she lays.
Ants which expect high quality, due to their experience on the first visit, undervalue the food, while ants which expect poor food overvalue it. We see this both in terms of acceptance behaviour and in pheromone deposition behaviour. The figure to the right shows the pilot data which inspired the project. The final results were published in eLife, and can be found here.
Many things affect value perception
the perceived value of an option can be affected by many other things, such as value-neutral expectations and the amount of effort invested to get something. These findings echo classic work in consumer psychology, so see that page for more details!