What makes house-hunting ants choose the best pad

April 22nd, 2009 - 3:10 pm ICT by ANI  

Washington, Apr 22 (ANI): When it comes to house-hunting, rock ants tend to choose the best home possible, according to a new study.

In the study, led by Dr Elva Robinson in the University’s School of Biological Sciences, researchers fitted rock ants with tiny radio-frequency identification tags, each measuring 1 / 2,000 (one two-thousandth) the size of a postage stamp.

They then observed as they chose between a poor nest nearby and a good nest further away.

And they observed that the ant colonies showed sophisticated nest-site choice, selecting the superior site even though it was nine times further away than the alternative.

The ants chose the best nest, despite the fact that very few individual ants made direct comparisons between the nest-sites.

For shifting to a new nest, scouting ants first discover new nests and assess them.

Then, scouts recruit nest-mates to the new nest using tandem-running, where an informed ant leads a second ant to her destination.

When the number of ants in the new nest reaches a quorum, scouts begin rapid transport of the rest of the colony by carrying nest-mates and brood.

In the study, very few ants appeared to make direct comparisons between the two nests by making multiple visits to each before choosing one or the other.

But, approximately half (forty-one per cent) of the ants that first visited the near nest later switched to the far nest, whereas only a tiny minority (three per cent) of the ants that first visited the far nest switched to the near nest.

And the entire colony thus ended up in the better nest.

“Each ant appears to have its own ‘threshold of acceptability’ against which to judge a nest individually. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies ended up in the good nest. Individual ants did not need to comparatively evaluate both nests in order for the entire colony to make the correct decision,” said Robinson.

She added: “On the other hand, animals - including humans - who use comparative evaluation frequently make ‘irrational’ decisions, due to the context in which options are compared or by inconsistently ranking pairs of options, (for example option A preferred to B, B preferred to C but C preferred to A).

“The ants’ threshold rule makes an absolute assessment of nest quality that is not subject to these risks, and circumvents the necessity for memorization and comparison of every site visited. Thus, simple individual behaviour substitutes for direct comparison, facilitating effective choice between nest sites for the colony as a whole.”

The research has been published in Proceedings of the Royal Society B. (ANI)

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