Marien,

first of all I repeat here that my practice in taxonomy is "to use
different name for different protoconchs". But the reason is not that I
consider this the only explanation of the facts (or even the best one for
all cases). I consider it the more probable in general, possible for most
cases, not necessarily for all. And I agree with most of your consideration
.... not with all.

At 11.05 15/10/2003 +0200, you wrote:
>....but nevertheless this is the onset of the
>drifting apart of the L daughter gene pool...

No: at least, not necessarily. Isolation means that there is no possibility
of gene flow. Do you have any evidence that a lecithotrophic egg cannot be
fertilized by a sperm from a planktotrophic male (or vice versa)?
Think for a moment that egg production be under environmental control: a
female produces eggs with more yolk when the environmental conditions would
conterselect planktotrophy (and vice versa). There is evidence that the
amount of yolk in the egg DOES REGULATE the length of the embryonic phase,
maybe in terms of speed of the embryogenetic events. In this case
poecilogony is not only the most parsimonious hypothesis but also the more
workable.
There is NO definitive EVIDENCE that having tow different developments
(lecith vs. plankt.) would mean always genetic isolation.


> my point is that if you accept the P/L switch as crucial,
>then there is no place for the concept op poecilogony.

Your reasoning is circular:
Different development is crucial in speciation => different development =
different species
you miss an important link:
different development "=" speciation (crucial is not enough)
There are lots of example where a feature is crucial and actually
accompanies speciation in a group (lets say changes in the radula, or in
the feeding way, or in the courtship, or in the colour pattern) and the
same feature is simply a polymorphism in another group.
In the first case you can use the feature as a diagnostic character. In the
other group ... simply you can't.

>We may not be right, but we're practical.
Taxonomy in fact is a tool in the hands of thos that use it. Monographs,
checklists, inventory of the biodiversity, ecological stusies, all require
a taxonomy usable. But we also know that the biological classification must
reflect the reality in the Nature.
All in all I keep considering our practice of giving different names to
different protoconchs as a good practice. It probably does reflect most of
the reality of Nature. BUT ... we must always keep in mind that Nature is
not rigid, likes to make exceptions, sometimes uses alternative, less
parsimonious ways.
That's what makes Evolution and Biology in general so different from
Physics and Chemistry.
And I love it.






=========================================================
Marco Oliverio - Evolutionary Biology PhD
Research Scientist

Dipartimento di Biologia Animale e dell'Uomo
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