ECOLOGY:

Animals make decisions all the time. Sometimes a fast impulsive reaction, and other times a slow thoughtful reaction, is more critical for survival.

Imagine a cheetah charging towards you. If you stop to think of the best hiding places and optimal direction to run, you've just become a cheetah-snack.

Now imagine a different scenario, in which your village is straight ahead at the other side of a clearning. You can choose to get there more quickly across the field, or more slowly along the high, defensible ridge above the field.

Here, a quick decision to choose the shorter path puts you at greater risk of attack (maybe by the hungry cheetah). Clearly, different situations require different reaction speeds and levels of thought.

Mammals' neural pathways are rigged such that information which needs to be processed quickly can bypass information of lesser importance. Given its presumed evolutionary advantages, one would expect such a capacity in other animals besides mammals.

However, there is little evidence of it in the scientific literature. Nathalie Stroeymeyt (University of Copenhagen, Denmark) and coworkers have demonstrated rapid and manipulatable decision-making with little neural processing in ants, for situations critical to their survival, based on chemical recognition.

This research is complimentary to the recent discovery that the caterpillar parasite Maculinea rebeli utilizes chemical and vocal trickery to bring themselves into Myrmika schencki ant society and establish a high societal status. It is also complimentary to the recent discovery that Acromyrmex ants secrete candicidin molecules to keep out unwanted fungi from their Leucoagaricus fungus gardens.

Ant nestmate recognition: Speed, manipulation, and neural processing.

The scientists' research is on Camponotus aethiops ants from Italy, collected in the spring of 2007. They were provided with plenty of water, fed mealworms and diluted honey, and kept at 24°C with 12 hours of light and 12 hours of darkness.

The scientists' first tests showed that, under restraint such that the ants stayed in place and could only move their heads, all of the ants (those which habituated to the restraint) exhibited rapid aggression (opened their mouths) in response to the odor of non-nestmates. Four responded within 160 milliseconds, and the other six responded within 120 milliseconds (the video recording was at a rate of 1 frame per 40 milliseconds).

The aggression response is fast. Can the response be manipulated?

The scientists either introduced the odor of non-nestmates into the colony via a slide for one day, or placed the appropriate chemicals in a capillary over the ants' antennae for 18 hours. In both cases, the ants were less aggressive to the odor, relative to ants instead pre-treated with nestmate odor.

The aggression response can be manipulated. Does the response require thorough neural processing?

Analogous decreased aggression results were observed when only one antennae was exposed, but only with the exposed antennae. In other words, the opposite side of the ants' brain was not responsive to conditioning.

Implications.

This research adds evidence to the hypothesis that other animals besides mammals can react quickly to potentially life-threatening situations without extensive neural processing. Ants clearly can use chemical cues to make rapid decisions, analogous to how mammals use sight and sound for similar purposes.

Further, the response can be manipulated to adjust for evolving conditions. The neurology, physiology, and chemistry of this dynamic recognition capability awaits further investigation.

NOTE: The scientists' research was funded by the European Union-Marie Curie Excellence Grant.

for more information:
Stroeymeyt, N., Guerrieri, F. J., van Zweden, J. S., & d'Ettorre, P. (2010). Rapid Decision-Making with Side-Specific Perceptual Discrimination in Ants PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0012377