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RE: [uk-ferns] Species

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  • Anthony Pigott
    Dear All I think Wim puts it very well. I would just add a few points: Nearly all taxonomists, in recent years at least, believe that biological
    Message 1 of 4 , Jan 1, 2010
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      Dear All

       

      I think Wim puts it very well.

       

      I would just add a few points:

       

      Nearly all taxonomists, in recent years at least, believe that biological classifications should be natural, that is follow the underlying evolutionary reasons for the variation we observe.  I agree with that.  Some (probably the majority today) take this too far,  in my opinion, insisting on all taxa being monophyletic, a single clade, all the descendants from a common ancestor. I think this is unnecessary as it fails to recognise all the ways that evolution works including speciation through hybridisation.

       

      It is notoriously difficult to find a definition of species that holds in all cases. This should not be surprising because speciation is often a messy affair, taking very long periods of time and with the outcome uncertain early on.  However, it seems that most of life does in fact divide itself into species (in the broad sense that members are much more like each other than they are like non-members) which most taxonomist agree on most of the time.  There are a lot of difficult special cases, as we should expect, mostly through speciation having only recently taken place or being still in progress.

       

      There are a number of these difficult cases in pteridophytes, mostly due to hybridisation, polyploidy and apogamy (or some combination of those). In these cases, some judgement has to be made. I believe that the best thing to do is to try to find taxa which are broadly equivalent to the ‘easier’ situations. A good approach, in my opinion, is to say that speciation has taken place (and therefore the resulting taxa warrant recognition at species level) when the two resulting populations are both reproductively isolated and phenotypically separated. 

       

      Differences in phenotype might be the more obvious gross morphology but also include microscopic morphology, cytology, chemical and molecular genetic characters.  Many biologists (probably most) these days seem rely almost entirely on molecular evidence to form their phylogenies and classifications.  I personally would not do that as, without an exact knowledge of how genetic material functions (which we are far from, despite many advances), molecular evidence is just more phenotypic characters, albeit very important ones.

       

      We should also remember that even if we focus on gross morphology, the ability of people to readily distinguish taxa is not fixed.  There was a time when most people found it difficult to separate the three Polypodium species,  the male-fern Dryopteris used to all be lumped together as D. f.-m., now many people are perfectly comfortable with several taxa within the D. aff. complex.  Peoples ability to identify is influenced by what they are asked to look for – taxa separated on cryptic characters are often subsequently found to have more obvious ones.

       

      Best wishes and a happy new year to you all!

       

      Anthony

       

      From: uk-ferns@yahoogroups.com [mailto:uk-ferns@yahoogroups.com] On Behalf Of Wim de Winter
      Sent: 23 December 2009 12:27
      To: uk-ferns@yahoogroups.com
      Subject: [uk-ferns] Re:Obscurantism!?

       



      Dear Chris and William,

      Without so much as disagreeing, or even trying to set up a coherent argumentation, I would like to add a few points that I think should not be missed in this discussion.

      Combining morphologically distinguishable and genetically distinguishable, one doesn't need much mathematicianity to see that there are four possible cases:

      1. taxa that are both morphologically distinguishable and genetically distinguishable: those are the classic species, no problems here.
      2. taxa that are neither morphologically nor genetically distinguishable: these are identical, a single taxon as we understand it now.
      3. "taxa" that are morphologically but not genetically distinguishable: this has traditionally been considered as "variation" and not as different taxa, or at best at a lower level.
      4. taxa that are not morphologically but only genetically distinguishable: is what has been called "cryptospecies".


      Evidently, it is the last category that prompted this discussion. But if morphology alone is given primacy here, wouldn't it then be only logical to separate the taxa of the third category? For why is morphology used one way, i.e. to combine, rather than to separate?

      Another thing that is troubling me, is: what exactly *is* morphologically distinguishable? In the early days of biology, anything swimming in the water in the happy possession of fins was a Fish, until some bright guy thought it an adventurous idea to study their insides too and guess! whales were quite different! Even looking closer a home, from the mid 18th Century until present, the amount of characters included in the distinction of species has gradually grown. Not only the concept of morphology is temporarily unstable, but also that of "distinguishable". Seeing his expert judgments here, I would say Chris can evaluate morphological differences that others can't. While some of his experience will permeate into the taxonomical community, other may remain his expert judgement. Extending this line of thought, one can imagine someone spending his entire life to an extremely limited group, finally being able to see differences that no-one else can see. Here I strongly agree that "practicality" should stand upon its dignity, but then I ask: practical to whom and when? The practicality of cytological research has improved a lot during the passed decades and is to be expected to continue improving rapidly in the years to come.

      Then wouldn't it be an artificial choice to exclude chromosome counts and genome compatibility? At least these are characters that can be observed by normal optical means as we have done for 250 years now. Why stop here? And what if the characters *were* entirely chemical? If I understood well, in mycology the chemistry is of utmost importance, likewise it is in bacterial taxonomy. Long ago, when I tried to distinguish lichens, I always caried a set of bottles with KOH, hypochlorid, and p-phenylenediamine.

      The meaning of a species as having "recognisability from morphology" seems rather incomplete. Species are the major unit of expression of biodiversity. Biodiversity thus expressed is just another mathematical number, but it stands for a certain experience of richness. Would that only be richness of forms (=morphology)? Or does richness in ecological roles also count? And what about future diversity, for cryptospecies are not expected to remain undistinguishable forever. While this is an entirely different discussion, the important point here is that if you see taxonomy as a serving discipline, you'd ought to take into consideration the needs of the disciplines served. Something similar could be said about pharmacy and chemically different "forms".

      cheers!

      Wim






    • chrisophilus
      Dear Anthony, I see that you do introduce the morphological element into a species concept a bit further down, but could I just add to your Nearly all
      Message 2 of 4 , Jan 1, 2010
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        Dear Anthony,
        I see that you do introduce the morphological element into a species concept a bit further down, but could I just add to your "Nearly all taxonomists, in recent years at least, believe that biological classifications should be natural, that is follow the underlying evolutionary reasons for the variation we observe." Yes, but please don't forget, right at the beginning, that nearly ALL taxonomists have always believed in having some acceptable degree of morphological distinction as well. This balance between the practical (sometimes "artificial") and biological has long been a basic principle re species-concepts. It is not ONLY the natural basis for species-concepts that counts - they should follow [i.e. more-or-less closely] the natural basis, but ALSO have practical considerations factored in!
        As you rightly say - only now for the first time do we get the majority (but not quite all of) the clado-moleculologists attempting to entirely ignore this. Or rather they don't try to ignore it, they simply don't have the ability to include it in their schemes.
        So the question is what is an acceptable degree of distinction? Nearly anyone would say that if it is purely a cytological difference and the taxon is almost entirely cryptic (except in resulting spore/stomatal size), that's simply not good enough for a species - as we can't then put a binomial name on it without a chromosome-count! I'd definitely say the same (in higher plants), as you do, about purely genetic differences, without the morphology.
        While I agree that the major taxa in, for example, the D. affinis agg. (surprise, surprise!) are now pretty widely accepted - it is not that they became more recognisable, more minutely, in time. They were always pretty recognisable on rather major morphological characteristics, often spottable from a passing bus etc. - only that people came to learn about them. Very minor microcharacters still remain something that we should consider very carefully if the thing is appropriate as a species or not. The rank of subspecies, often underused today, and not even known to molecular cladonomists, becomes a very important one in such circumstances, especially when there is a known biological connection.
        The difference of degree between a "biological-species conceptualist" and a "taxonomic-morphological conceptualist" is a very important one - and I rather feel that while the latter include the former considerations within their concept, the former often simply don't trouble to do so and tend to forget about it, leading to some most unfortunate situations of people struggling with the impossible in order to put a name on things that can hardly be recognised by human beings!
        Let's not forget or ignore the essential balance - the botanical middle way, if you like, right at the initial basis of any species-concept!
        Cheers,
        Chris.



        --- In uk-ferns@yahoogroups.com, "Anthony Pigott" <Anthony.Pigott@...> wrote:
        >
        > Dear All
        >
        >
        >
        > I think Wim puts it very well.
        >
        >
        >
        > I would just add a few points:
        >
        >
        >
        > Nearly all taxonomists, in recent years at least, believe that biological
        > classifications should be natural, that is follow the underlying
        > evolutionary reasons for the variation we observe. I agree with that. Some
        > (probably the majority today) take this too far, in my opinion, insisting
        > on all taxa being monophyletic, a single clade, all the descendants from a
        > common ancestor. I think this is unnecessary as it fails to recognise all
        > the ways that evolution works including speciation through hybridisation.
        >
        >
        >
        > It is notoriously difficult to find a definition of species that holds in
        > all cases. This should not be surprising because speciation is often a messy
        > affair, taking very long periods of time and with the outcome uncertain
        > early on. However, it seems that most of life does in fact divide itself
        > into species (in the broad sense that members are much more like each other
        > than they are like non-members) which most taxonomist agree on most of the
        > time. There are a lot of difficult special cases, as we should expect,
        > mostly through speciation having only recently taken place or being still in
        > progress.
        >
        >
        >
        > There are a number of these difficult cases in pteridophytes, mostly due to
        > hybridisation, polyploidy and apogamy (or some combination of those). In
        > these cases, some judgement has to be made. I believe that the best thing to
        > do is to try to find taxa which are broadly equivalent to the 'easier'
        > situations. A good approach, in my opinion, is to say that speciation has
        > taken place (and therefore the resulting taxa warrant recognition at species
        > level) when the two resulting populations are both reproductively isolated
        > and phenotypically separated.
        >
        >
        >
        > Differences in phenotype might be the more obvious gross morphology but also
        > include microscopic morphology, cytology, chemical and molecular genetic
        > characters. Many biologists (probably most) these days seem rely almost
        > entirely on molecular evidence to form their phylogenies and
        > classifications. I personally would not do that as, without an exact
        > knowledge of how genetic material functions (which we are far from, despite
        > many advances), molecular evidence is just more phenotypic characters,
        > albeit very important ones.
        >
        >
        >
        > We should also remember that even if we focus on gross morphology, the
        > ability of people to readily distinguish taxa is not fixed. There was a
        > time when most people found it difficult to separate the three Polypodium
        > species, the male-fern Dryopteris used to all be lumped together as D.
        > f.-m., now many people are perfectly comfortable with several taxa within
        > the D. aff. complex. Peoples ability to identify is influenced by what they
        > are asked to look for - taxa separated on cryptic characters are often
        > subsequently found to have more obvious ones.
        >
        >
        >
        > Best wishes and a happy new year to you all!
        >
        >
        >
        > Anthony
        >
        >
        >
        > From: uk-ferns@yahoogroups.com [mailto:uk-ferns@yahoogroups.com] On Behalf
        > Of Wim de Winter
        > Sent: 23 December 2009 12:27
        > To: uk-ferns@yahoogroups.com
        > Subject: [uk-ferns] Re:Obscurantism!?
        >
        >
        >
        >
        >
        > Dear Chris and William,
        >
        > Without so much as disagreeing, or even trying to set up a coherent
        > argumentation, I would like to add a few points that I think should not be
        > missed in this discussion.
        >
        > Combining morphologically distinguishable and genetically distinguishable,
        > one doesn't need much mathematicianity to see that there are four possible
        > cases:
        >
        > 1. taxa that are both morphologically distinguishable and genetically
        > distinguishable: those are the classic species, no problems here.
        > 2. taxa that are neither morphologically nor genetically
        > distinguishable: these are identical, a single taxon as we understand it
        > now.
        > 3. "taxa" that are morphologically but not genetically distinguishable:
        > this has traditionally been considered as "variation" and not as different
        > taxa, or at best at a lower level.
        > 4. taxa that are not morphologically but only genetically
        > distinguishable: is what has been called "cryptospecies".
        >
        >
        > Evidently, it is the last category that prompted this discussion. But if
        > morphology alone is given primacy here, wouldn't it then be only logical to
        > separate the taxa of the third category? For why is morphology used one way,
        > i.e. to combine, rather than to separate?
        >
        > Another thing that is troubling me, is: what exactly *is* morphologically
        > distinguishable? In the early days of biology, anything swimming in the
        > water in the happy possession of fins was a Fish, until some bright guy
        > thought it an adventurous idea to study their insides too and guess! whales
        > were quite different! Even looking closer a home, from the mid 18th Century
        > until present, the amount of characters included in the distinction of
        > species has gradually grown. Not only the concept of morphology is
        > temporarily unstable, but also that of "distinguishable". Seeing his expert
        > judgments here, I would say Chris can evaluate morphological differences
        > that others can't. While some of his experience will permeate into the
        > taxonomical community, other may remain his expert judgement. Extending this
        > line of thought, one can imagine someone spending his entire life to an
        > extremely limited group, finally being able to see differences that no-one
        > else can see. Here I strongly agree that "practicality" should stand upon
        > its dignity, but then I ask: practical to whom and when? The practicality of
        > cytological research has improved a lot during the passed decades and is to
        > be expected to continue improving rapidly in the years to come.
        >
        > Then wouldn't it be an artificial choice to exclude chromosome counts and
        > genome compatibility? At least these are characters that can be observed by
        > normal optical means as we have done for 250 years now. Why stop here? And
        > what if the characters *were* entirely chemical? If I understood well, in
        > mycology the chemistry is of utmost importance, likewise it is in bacterial
        > taxonomy. Long ago, when I tried to distinguish lichens, I always caried a
        > set of bottles with KOH, hypochlorid, and p-phenylenediamine.
        >
        > The meaning of a species as having "recognisability from morphology" seems
        > rather incomplete. Species are the major unit of expression of biodiversity.
        > Biodiversity thus expressed is just another mathematical number, but it
        > stands for a certain experience of richness. Would that only be richness of
        > forms (=morphology)? Or does richness in ecological roles also count? And
        > what about future diversity, for cryptospecies are not expected to remain
        > undistinguishable forever. While this is an entirely different discussion,
        > the important point here is that if you see taxonomy as a serving
        > discipline, you'd ought to take into consideration the needs of the
        > disciplines served. Something similar could be said about pharmacy and
        > chemically different "forms".
        >
        > cheers!
        >
        > Wim
        >
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