Friday, July 30, 2010
You're a scientist, and you're thiiiis big. Right, ok, nevermind. How do you design an experiment to see how ants measure distance?
I'll give you a second to think on it...
You're gonna love this one. So, it is known that ants use the sun kinda like a compass so they know which direction they are going, and they have a component in their brains which acts as a body clock so they know how long they've been gone. Well, this paper published in the Journal of Experimental Biology shows how ants count their steps in order to judge distance.
In the study, researchers used Desert ants (Cataglyphis fortis) from a field site near Maharès, Tunisia. First, they trained the ants (Fun Job #1: Training ants) to walk a distance of 10 m in a linear alloy channel from their nest entrance to a feeder due south and back again. All the ants got marked with a color (Fun Job #2: Painting ants) and their leg lengths were manipulated to test their ant-odometers. And here's where we get creative. The researchers wanted to both shorten, lengthen, and keep the same various ants' legs, altering their stride length. To shorten, tarsal segments were removed or the legs were severed mid-tibia (snip, snip). To lengthen the legs, hairs from a pig were individually Superglued onto the end of each leg, extending it by about 2-3 mm (Fun Job #3: Supergluing itty-bitty hairs to itty-bitty ant legs). Oh yeah, ants on stilts!! They allowed the ants to go from their nest to the feeder, there they altered their leg length, allowed them to pick up some food, and then let them try to find their way home. Using a high-speed camera, the ants were filmed as they walked down the channel (Fun Job #4: Going through high speed video frame by frame counting ant steps). The results showed that ants that had their legs lengthened overshot their nests, and ants that had their legs shortened didn't walk far enough. If the ants-on-stilts or ants-with-stumps went to the feeder from the nest and then back again they judged the distance correctly, showing that they have the ability to quickly adjust to their new leggy situation. The paper itself goes over supporting/rejecting various hypotheses as to why, but as I'm just focusing on the fact that they put ants on stilts I'll leave the discussion section of the paper for you to read.
Here's your reference:
Wittlinger, Matthias, Rüdiger Wehner and Harald Wolf (2007) The desert ant odometer: a stride integrator that accounts for stride length and walking speed. Journal of Experimental Biology: 210, 198-207. (DOI: 10.1242/jeb.02657) (or this Link)
(image credit to the Max Planck Institute for Chemical Ecologists, Markus Knader)