From: swf@teradata.com (Stanley Friesen)
Newsgroups: talk.origins
Subject: Re: Origin of Carnivorous Plants
Date: 27 Sep 92 17:13:30 GMT
Reply-To: swf@tdat.teradata.com (Stanley Friesen)
Organization: NCR Teradata Database Business Unit

In article <7063@tekig7.PEN.TEK.COM> alanf@tekig6.PEN.TEK.COM (Alan M Feuerbacher) writes:
|   The research refutes the common assumption that carnivorous plants
|   are all closely related.  It shows that even plants with the same
|   method of trapping prey may be only distantly related and arrived at
|   their similar ways of life through convergent evolution.
|
|   For example, the various `pitcher plants,' whose scents lure insects
|   into a vat of digestive juices, arose independently at least three
|   times.  The `flypaper' way of life, with its sticky secretions on the
|   surfaces of leaves, was `invented' at least five times.

Goodness, its amazing what papers will use for filler.  The classification
of flowering plants 10 years ago already implied this for those who paid
attention.  This is hardly news.

|How can several plant varieties have evolved the complex mechanisms
|required to catch insects, then digest and utilize the nutrients,
|completely independently?  The evolutionary mechanisms alluded to by
|Dawkins in _The Blind Watchmaker_ seem inadequate to the task of
|having *all* the required mechanisms evolve simultaneously.  If
|they did not evolve simultaneously, what advantages can be proposed
|to allow the individual mechanisms to be selected for?

Sigh.  It is a general result of paleontology and comparative anatomy that
truly advantageous adaptations tend to occur repeatedly.  Eyes, wings,
sharp teeth, and many many more, are examples of such.  

The *individual* mechanisms are *not* selected for in *particular*, only
the *results*.  That is why there are *three* mechanisms (at least) for
'carnivory' in plants.  Which every one of these mechanisms happened to be
closest to where the ancestral plant *already* *was*, was the one that
got enhanced in any given lineage.  In a lineage of plants with resinous,
or otherwise sticky, leaves, carnivory by enhancing this stickiness would
be favored in those environments where carnivory is a significant advantage.
In a lineage of plants with large leaves that tend to catch water (such
as many groups of tropical epiphytes) the easiest course to carnivory
would be the 'pitcher-plant' style.  [And, oh by the way, resinous leaves
are quite common, even in non-carnivorous plants - we tend to call these
plants 'aromatic'].

A survey of the carnivorous plants will show that they are *all*, every
one, herbaceous denizens of very nutrient depleted environments - permanent
swamps and bogs in particular.  Thus it is clear that for a plant with a
limited root system in a nutrient poor swamp environment, an additional
mechanism for gaining nutrients would be a *major* advantage.  Indeed
even a slight tendency to absorb nutrients from insects accidentally trapped
in the water-filled leaf or on the slighhly sticky resinous leaf, would
be enough to signficantly enhance the reproductive efficiency of the plant
in question.  (That is even a very *minimal* version of carnivory, or rather
scavenging, is advantagsous in this situation, so the 'a partial wing is
useless' argument doesn't even apply).

|For example, if a plant mutation resulted in sticky leaves, what selective
|advantage might be proposed to carry that along until the plant evolved
|the appropriate digestive enzymes and the mechanism to secrete them?

Whatever it is, it must exist, since such plant do exist.  They are even
quite common.  For instance the common (here) species Mimulus longiflorus,
commonly known as the 'sticky monkeyflower', is *quite* sticky, and it
most definately is *not* carnivorous.  Quite a few species of composite
have sticky leaves or a sticky flower head, especially desert species.
[Hmm, the climate here is generally at least sub-desert, so this feature
seems to be correlated with dry climates - perhaps it is a way of avoiding
dessication].

Or, for instance, large leaves that retain water, which I have said are
common in tropical epiphytes, are useful in giving plants with no connection
to the soil a semi-permament source of water for photosynthesis.

-- 
sarima@teradata.com			(formerly tdatirv!sarima)
  or
Stanley.Friesen@ElSegundoCA.ncr.com
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