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Some Botanical Fun



Dear Friends of Botanical Curiosity,

There is an interesting article in the October 5, 2007 issue of Science magazine entitled "Odor-Mediated Push-Pull Pollination in Cycads". The reason I feel comfortable about sharing it to this list is that the "push-pull" mechanism involves the warming of the cycad inflorescence and the emission thereby of chemicals. Sounds like some aroids, no?

It seems they have a cycad in Australia called Macrozamia lucida and they (especially the male) self-heat daily. This involves a temperature rise of 12 degrees C above ambient. This cycad is pollinated by a thrips (and some of you thought thrips were solely placed on earth the vex horticulturists) of a primitive thrips species called Cycadothrips chadwicki. During the hours of 1100 and 1500 (11 in the morning to 3 in the afternoon) the male plant heat up, emitting "male volatile emissions", which are attractive to thrips in the absence of heat. Evidently, the warmed male odors are obnoxious and/or toxic and drive the thrips, laden with pollen, out of the male plant and toward the less-noxious female plant. The article states that thrips that remain tend to die within ten minutes.

Once the heating cycle ends, the chemical activity and toxicity dissipates and the odor reverts to being attractive to thrips again, whereupon the thrips migrate back to the male cycad for another load of pollen. They then discuss the specific chemicals and some experiments they did, which may be less interesting to the general reader.

Finally, the article wraps up by observing "Floral scent may have originally evolved to deter herbivores, and this system may represent a conserved early intermediary in the evolution of seed plant pollination." There are some interesting speculations there for the botanically- and paleontologically-inclined.

For reasons I do not understand, the whole article can be read without charge at the Science magazine site:

http://www.sciencemag.org/cgi/reprint/318/5847/70.pdf

They also claim to have a movie clip showing the mass exodus of thrips, but I could not get it to download to my computer.

We tend to think of odor production in aroids as strictly attractive. But I wonder if some repellency might also take place in order to force pollen to another plant. Otherwise, why would a bug ever leave?

Ted.
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