Christian,
 sorry to press you a bit. What is your practical definition of
species/subspecies?
Ed
----- Original Message -----
From: "Cristian Ruiz Altaba" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, July 08, 2004 9:36 AM
Subject: what is a mollusc species?


> Dear colleagues,
>
> Species, most contemporary biologists would argue, are real entities.
>  These are lineages formed by intertwinning ancestor-descendant
> relationships, so they all consitute a single evolutionay unit that
changes
> through time.  We can see a species as a rope made of numerous fibers,
> which at some points fuse and at others break apart, but making a firm
> wire.
>
> Such a rope can, of course, fray apart.  This happens, for example, when
> something like the isthmus of Panama appears in between.  The question,
> obviously, is when will the two resulting threads might become distinct
> enough as to prevent interbreeding when someone builds a transoceanic
> canal.  The answer, alas, is far from evident.
>
> Sometimes telling species apart is easy, because of characteristic color
or
> sculpture patterns.  Often, malacologists need much experience to confront
> a given family, because the traits are subtle, or variable, or even
> overlapping.  We all know how futile it can be to follow an identification
> key to shells, just because so much variation and traits ought to be taken
> into account.  However, nobody ever said that species should be easy to
> tell apart!
>
> In taxonomic practice, all available evidence must be taken into account.
>  And the more, the better --that is why we struggle with molecular
> genetics, statistics, and so on.  The bottomline, I believe, is pretty
much
> what Mayr said: two populations living together in the very same spot and
> habitat, but showing no intermediates or other signs of interbreeding.  A
> situation like this one is what provides a yardstick for evaluating (i.e.,
> making a scientific hypothesis) the rank (species vs. subspecies vs.
> nothing) of related populations that are not living in that same spot.
>
> For example, I had to wrestle with Moroccan melanopsids, a puzzle for
> everyone.  However, luck stroke me when I found two sympatric populations,
> differing in rather subtle shell features, but having small but clear-cut
> genetic differences.  And no single hybrid around.  This was the yardstick
> to disentangle the rather complex pattern of melanopsid evolution in the
> rivers of North-west Africa.
>
> In my own opinion, then, species are out there, and we keep trying to know
> and celebrate the diversity of life.  Scientific research must be open, so
> it is unavoidable, and desirable as well, that different experts will have
> contrasting hypotheses that need to be tested by reality.  There will
> always be difficult groups to look at, and that is what makes malacology
> most interesting: you are doing hard science from the very onset, you can
> always learn more, yet you are never enough of an expert.  Or so I feel.
>
> Very best wishes,
>
> Cristian R. Altaba
>
> -----Mensaje original-----
> De:     Eduard [SMTP:[log in to unmask]]
> Enviado el:     jueves 8 de julio de2004 07:08
> Para:   [log in to unmask]
> Asunto: Re: Ernst Mayr
>
> Dear Tom and all
>
> Perhaps one possible way to move forward with species problems is to go
> from
> simple to more complicated: first agree on species definition from a
> conchological point of view and after that to think about more complicated
> biological aspects of the problem. In such a way we can at least gather
> facts and understand better what we are talking about. I do not think that
> number of species and subspecies "depends on your personal approach to
> taxonomy and the purposes and methodologies of distinguishing between one
> species and another." We need definitions of taxa, which are more or less
> in
> consensus and understandable to most of us.
>
> Because many members of this forum are shell collectors, I suggest to this
> List to start a discussion in order to work out at least  primitive
> (conchological) species and subspecies definitions.
>
> Eduard Heiman
>
> ----- Original Message -----
> From: "Thomas E. Eichhorst" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, July 07, 2004 7:45 PM
> Subject: Re: Ernst Mayr
>
>
> > Thanks John, that was a great read!  Mayr's definition of species is one
> of
> > many useful concepts he originated.  "A species is a group of actually
or
> > potentially interbreeding natural populations reproductively isolated
> from
> > other such populations."   Of course, the kicker is that "reproductively
> > isolated" part.  Thus the small green nerite, Smaragdia viridis, found
in
> > the Caribbean and the Mediterranean could be separated into two species
> (of
> > course the literature is still fighting over subspecies status).  The
two
> > populations are sufficiently visibly different to enable almost anyone
to
> > separate them and the populations are reproductively isolated.  They may
> > have interbred at one time (maybe around the Miocene), but the veligers
> are
> > no longer able to make the transatlantic journey.  If one believes in
> > natural selection and speciation, then these two populations have been
on
> > that track for quite some time.  The question is where/when do we draw
> the
> > line and say, "Okay, you are now two different species."
> >
> > Perhaps Mayr's greatest contribution is that he sees this "grayness" to
> > biology and does not believe we can finitely quantify this science with
> > numbers.  Thus statistical analysis and cladograms are eminently useful
> > tools, but they are only tools, part of a larger equation that also
> relies
> > upon field and lab observation and research.  The numbers can "prove" a
> > close relationship between a clam and an echinoderm - but our eyes and
> > experience tell us this is patently ridiculous.  A cladogram does very
> well
> > at pointing out possible and probable ancestral relationships, but falls
> > short when used for classification of living species - even though it so
> > often looks like it does just that.  Similarly, a statistical analysis
of
> > dimension, tooth count, weight, etc. between shells is an useful tool as
> > long as one never believes this is the final answer.  It can demonstrate
> the
> > bell curve of variation within a population but I believe will always
> fall
> > short of differentiating species.
> >
> > All of the above is a layman's opinion and I am in way over my head, but
> > always enjoy a good argument.
> >
> > Tom Eichhorst in New Mexico, USA
> >
> > > -----Original Message-----
> > > From: Conchologists of America List
[mailto:[log in to unmask]]On
> > > Behalf Of John Wolff
> > > Sent: Wednesday, July 07, 2004 7:20 AM
> > > To: [log in to unmask]
> > > Subject: Ernst Mayr
> > >
> > >
> > > July 5 was the 100th birthday of eminent biologist Ernst Mayr.
> > > He made major contributions to the concept of species.
> > > A summary of his accomplishments and an interview of this remarkable
> > > scientist done 5 years ago is available at
> > > http://www.skeptic.com/eskeptic07-05-04.html
> > >
> > > John
> > >
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