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