Ant garden myrmecochory, the effect of chemical compounds?

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Ant garden myrmecochory, the effect of chemical compounds?

Post by Benoit Guenard on Tue Jan 29, 2008 7:02 pm

In the early version of PNAS (edition of the 22nd of January 2008) is available an article on the attractiveness and the importance of chemical compounds of the seeds of an ant-garden plant.
Here are the reference of the article:

Elsa Youngsteadt, Satoshi Nojima, Christopher Häberlein, Stefan Schulz, and Coby Schal
Seed odor mediates an obligate ant–plant mutualism in Amazonian rainforests

I think the article is interesting on two aspects.
First, it shows that plant have developed some kind of chemical cues to attract the ants and to be dispersed by the ants in specific location. An other aspect in this process which I think very cool is that the chemical compounds implied in the seed dispersal process are some that are usually found in animals or in fungi, but not in plant. It is in that case, a real chemical mimicry from the plant to "cheat" the ant. At the same time, this compound seems to be specific to Camponotus femoratus or at least to a small number of ants. However, some experiments to test the specificity of the attractiveness on C. femoratus could be interesting to be sure that the fact that 85% of the seeds are dispersed by this species not the result of a more efficient behavior from this ant.

Secondly, I think that the design of the olfactometer is really elegant to test different chemical compounds and their effect on ants. However at this point, I have a problem with the method they have used.
For each replicate (that they call trial), they gave the choice to the ants the choice between a right or left arm (one having the tested compound). The first ant arrive and choose one of the arm (left or right), if the ant is attracted by the volatile compounds, the ant should choose the good one.
At some point, I suppose the ant leaves the olfactometer. If the ant has found the good path, it seems to me that there is a good chance that the ant will let a pheromone trail (not in the case the ant has chosen the "wrong" arm). If it is right, in that case, the next ant is not "naive" anymore because has information from the previous ant. And this continue until they reach the end of the trial after 30 ants. I doubt that the ants which followed the first one is still neutral, and even less for the 30th one.
The authors have cleaned the system and alternate the emission (on the right or on the left) after each trial, but this is after the passage of 30 ants! To me they should clean and change the tubes after each ants.

I agree with the authors that some chemical cues are implied in the seed dispersion process, but I don't know if I can trust their results on the specific compounds they have tested.

What do you think about it?
Neil, do you have other examples of the use of chemical compounds in the seed dispersal processes in Australia or somewhere else?
Benoit Guenard

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Registration date : 2008-01-19

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