Re: vital effect and genetics

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>        My topic is the vital effect and it's possible use in determining
>paleospecies.  The basic premise is that the vital effect is a biological
>influence on the isotopic composition of shells and tests.  Suppose you had a
>bunch of forams (or something) and you wanted to know how many species are
>represented.  They all look about the same, so physical characteristics won't
>help much.  So, you turn to isotopes.  Given that these forams were living in
>the same region at the same time, then any isotopic differences must be
>genetic.
>You can eliminate such other factors that can influence the isotopic
>composition
>as diet (they look the same, they probably lived that same), temperature,
>water,
>and climate.  That leaves the vital effect.  Since the vital effect is
>biological, it must have genetic roots.  Therefore, different but closely
>related species ought to have subtle differences in their vital effect.  The
>question is, is this difference detectable?

I can't see how you can rule out the various environmental/ecological
factors, including diet, autotrophic symbionts, and various physiological
niceties as causes of isotopic variation, just on the basis that the
organisms lived in the same region at the same time. A "bunch of forams"
from the same sample may occupy a whole suite of microenvironments, eat
different things, live at different sediment depths, grow at different
times, etc. Saying that "since the vital effect is biological, it must have
genetic roots" seems a very circular way of putting it. Isn't the "vital
effect" just shorthand for "effects we can't find an environmental cause
for"? That's a far way from proving that it is due to some genetically
determined fractionation mechanism. If different but closely related
species have subtle differences in their "vital effect", it may be due to
subtle differences in their mode of life. The isotopic signatures might
still be of some taxonomic use, but if the processes are not understood the
method seems rather hazardous.

Stefan Bengtson                      _/        _/ _/_/_/    _/        _/
Department of Palaeozoology         _/_/      _/ _/    _/  _/_/    _/_/
Swedish Museum of Natural History  _/  _/    _/ _/    _/  _/  _/ _/ _/
Box 50007                         _/    _/  _/ _/_/_/    _/    _/  _/
S-104 05 Stockholm               _/      _/_/ _/   _/   _/        _/
Sweden                          _/        _/ _/     _/ _/        _/

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