Dear friends:

The core concept of comparative biology is the species.  Every talk about
biodiversity and its conservation should be firmly based on this (otherwise
we get "rough genetic" biodiversity chats, or "satellite-view ecosystem"
approaches).  The important issue, thus, is finding out what are the
species boundaries.

Within a given species, it often happens that its geographic range is not
continuous, so that populations from different areas differ in some traits.
 Often these differences are just the outcome of environmental conditioning
(e.g., shell height vs. tide exposure within a limpet species), or due to
the interaction of a common genetic background with particular environments
(e.g., the frequency of color and banding patterns in Cepaea).

However, in other cases it is clear that there are genetic differences
underlying the observable diagnosable traits.  These differing populations
may evolve into different species or not, but as long as we have no evid
ence of speciation (the process of establishing reproductive barriers),
then it is wise to view them as belonging to the same species --i.e.,
subspecies.

In a nutshell: the formal recognition of molluscan subspecies seems no
simple job, because you first have to figure out both what are the species,
and what is the range of variation within and among undifferentiated
populations.  It is quite unclear whether this can be done by looking only
at the shell.

Best wishes,

Cristian

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