Comments on: The Semiotics of a Leaf

By: mathew

mathew — Sun, 08 Jan 2006 15:38:42 +0000

hi…
am a final year botany student. i wish to get some information regarding poilnators in birds. this is for my thesis work. kindly help me if possible.
thankyou

By: Rob Bate

Rob Bate — Mon, 07 Nov 2005 04:59:54 +0000

The summer color of trees is a combination of chlorophyll, which is a deep blueish green, carotene, a yellow orange as in carrots and anthocyanin. the red described above. The rich blue/green coupled with the yellow orange and red mix into the relatively neutral yellow green common to most midsummer leaves.

I assumed that when the chlorophyll was reabsorbed or broke down the yellows, oranges and reds were left as a beautiful, but essentially functionless, byproduct. Has any purposeful use of fall color been established?

By: Gene Norman

Gene Norman — Wed, 02 Nov 2005 23:24:58 +0000

Carl,
I’m don’t study these thing scientifically, but the aborists/foresters here in Wisconsin tell us that a tree which colors early, or much brighter than similar surrounding trees is under some kind of stress, including drought and insect attacks. Can you: a. dispute/corroborate this and/or
b. include it in your theory?

By: Patrick Foss

Patrick Foss — Wed, 02 Nov 2005 17:11:16 +0000

Does anyone know if the colorless toxins are also odorless? Saying that the color alone deterred the insects may lead to an erroneous assuption that the color was responsible when in fact it may indeed be incidental and that the odor or taste of the toxins are apparent to an insect when it first lands on the tree.

By: David Winter

David Winter — Tue, 01 Nov 2005 04:40:38 +0000

Carl,

I’ve enjoyed all your stories about the autumn colours, thanks for bringing such a cool topic to the attention of your readers.

If one of the co-evolutionary theories is actually going on it would be cool to find trees that cheat. That is, trees that don’t produce toxins or use colours for ‘honest signalling’ like Hamilton’s idea but freeload on the effort put in by other tress doing those things. Once aphids avoid red leaves you might get away with just producing red leaves to reduce your parasite load.

By: Perry

Perry — Mon, 31 Oct 2005 16:17:40 +0000

My understanding of colour change was given to me in 1960 by my Botany teachers. Put simply, abscission cells at the base of each leaf slowly grow if a leaf uses more sugar than it creates. As the green chlorophyll deteriotes the underlying colour become more evident until the leaves dry and drop. The rationale then, was that the leaves would be a liability as they would increase the “top hamper” effect during the winter gales.

“Perhaps a tree could send a message to insects looking for a place to lay their eggs: stay away from me or I’ll kill your kids in the spring.”

How would that work? The leaves would have died and be well on their way to become leaf mould.

This is an example of over complication. Dare I suggest that the simple explanation is probably the more correct, however, you chaps are very fortunate to have such beautiful colours at this time of the year. In NW London, our trees just seem to go yellow and drop. No maples!

By: Bruce Amiata

Bruce Amiata — Mon, 31 Oct 2005 12:40:55 +0000

Is it not also the case that most insects (the polinating ones, anyway) detect light shifted towards the blue, rather than the red? (Bird polinators, generally, are attracted to the red end of the spectrum). I wonder how much discrimination insects have from green through the yellow and red portion of the spectrum…

By: Peter Ellis

Peter Ellis — Mon, 31 Oct 2005 08:52:51 +0000

The obvious approach, it seems to me, would be to study the sequence of anthocyanin-producing genes and the toxin-producing genes in a range of different species.

That might tell you whether the colours came first or the toxins came first, which would in turn be a clue to their function. The scenario described above looks very like one where a biological pathway producing pigment molecules for defence against UV was later extended to generate toxins

Heck, you could even look at the evolution of insect eye pigment genes. Maybe insects see red because tree leaves are red, not vice versa.

By: Andrew Brown

Andrew Brown — Mon, 31 Oct 2005 08:38:45 +0000

Carl, we’re getting into very deep water here. Does a signal require an attempt to communicate, or is it something constructed in the behaviour of the beholder? Dennett, I think, would plump unequivocaly for the latter. In this, as in most things, he is merely making explicit assumptions that a lot of scientists hold. Signals, or informaiton more generally, are not properties of things in themselves, but of their interactions with the world.

I suppose the test, in evolutionary terms, would be to see whether the colouring of leaves was maintained only if it functioned as a signal: in other words, if it didn’t protect against UV light as well. But since protection against UV light also increases the amount of some toxins, I don’t see how the experiment could, even in theory, be done. There’s a double effect that can’t be disentangled.