[Taxacom] FW: Why Australians are more real than Americans: implications for taxonomy!

Stephen Thorpe s.thorpe at auckland.ac.nz
Mon Sep 7 04:12:25 CDT 2009


Brian,
I think the question is this:
If you have two individual asexual lines of descent that consistently differ only very, very slightly from one another (so there is a gap), is there any objective meaning to them being the same or different species, or is it up to the taxonomist to decide?
Cheers,
Stephen

________________________________________
From: bti at dsmz.de [bti at dsmz.de]
Sent: Monday, 7 September 2009 9:08 p.m.
To: Stephen Thorpe
Cc: taxacom at mailman.nhm.ku.edu
Subject: RE: [Taxacom] FW: Why Australians are more real than Americans:        implications for taxonomy!

Stephan,
As for asexuals, there appear to be breaks and gaps because diversity
is removed during the course of evolution (yes I know this is vague).
If this were not the case at the genetic level one would see a
continuous spectrum with there being one base change at a time (again
a simplistic model). In the case of sexually reproducing organisms,
whether one can observe sexual reproduction this is one of the
criteria. In asexual organisms, then you have one less parameter to
define "species", which makes things more difficult.

Brian



Quoting Stephen Thorpe <s.thorpe at auckland.ac.nz>:

> Well done Brian! Important to be clear about this:
> Richard Pyle (and possibly others like Jim Croft) don't appear to
> have a biological understanding of what species are! Their concept
> of species appears to be the more general one that could apply just
> as easily to rocks and minerals. The example which I think shows
> this the best is the one about 2 (or more) allopatric populations
> which are consistently different, but the morphological gap is so
> narrow that most taxonomists would not give it any species-level
> significance. I (and also Mayr, if I understand him) would say that
> whether or not the two populations are distinct species depends on
> facts about reproductive isolation. Richard seems to think that it
> is a purely subjective choice to consider them distinct species or
> not...
>
> Still not sure about asexuals! Maybe their species boundaries really
> are subjective ...
>
> ________________________________________
> From: taxacom-bounces at mailman.nhm.ku.edu
> [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of bti at dsmz.de
> [bti at dsmz.de]
> Sent: Monday, 7 September 2009 7:54 p.m.
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] FW: Why Australians are more real than
> Americans:      implications for taxonomy!
>
>  From
> http://www.pnas.org/content/102/suppl.1/6600.full
> Ernst Mayr and the modern concept of species
> Kevin de Queiroz
>
> "However, an examination of Mayr's writings on species reveals he had
> good reason for selecting this adjective. According to Mayr (42, 43),
> ?This species concept is called biological not because it deals with
> biological taxa, but because the definition is biological. It utilizes
> criteria that are meaningless as far as the inanimate world is
> concerned.? The important idea for Mayr was that earlier concepts of
> species were based on properties, such as degree of difference, that
> could be applied just as easily to inanimate objects as to living
> things. Linnaeus (44), for example, recognized species not only of
> plants and animals but also of rocks and minerals. In contrast, a
> truly biological concept of species must be based on properties that
> are unique to biological systems, properties such as reproduction and
> interbreeding."
>
> The problem that arises is that if a definition is attached to
> something that is not a universal feature then the definition should
> be re-defined to fit the biology of the organisms concerned. The
> simple dictionary definition of species is "a sort or kind". In
> sexually reproducing organisms one uses that biological feature to
> define that "sort or kind". I think it is well known that Simpson and
> Mayr had to juggle with how much interbreeding does one allow between
> species without calling into question that one has two species and not
> one.
>
> Asexual "things" diverge and evolve as do sexual "things" the only
> major difference being that they don't need partners to do it.
>
> Brian
>
>
> Quoting Stephen Thorpe <s.thorpe at auckland.ac.nz>:
>
>> Just to preempt a rather obvious objection to what I said below, one
>> might object that if ANY consistent morphological gap defines a
>> species, then probably every INDIVIDUAL will end up being a
>> different species! Two possible replies:
>>
>> (1) We look for morphological gaps between POPULATIONS, not
>> individuals! Only if there is a consistent morphological gap between
>> every individual in one population compared with another are the two
>> populations to be considered distinct species, no matter how small
>> the gap. Problem: how do you define population? I think we end up at
>> (2) below, whichever way we try to go:
>>
>> (2) the biological species concept (i.e., reproductive isolation
>> under natural conditions) is the only way to go, and cannot be
>> avoided without ending up in contradiction! We can never be sure if
>> two populations would maintain reproductive integrity, but science
>> is all about making hypotheses based on evidence, and that is
>> exactly what we must do! If the genitalia are quite different
>> between populations, for example, then we hypothesise that this
>> difference is sufficient to ensure reproductive isolation. And in
>> fact a population itself is a "dispersively connected" bunch of
>> individuals for which we hypothesise no barriers to reproduction.
>>
>> So if one taxonomist says it is that species, and another says not,
>> there will be a right answer depending on the presence/absence of
>> reproductive barriers in the hypothetical event of the two
>> populations "coming together" under natural conditions. We can never
>> no FOR CERTAIN, but that is true of most things...
>>
>> Not sure where this leaves asexual things...
>>
>> Stephyen
>>
>> ________________________________
>> From: Stephen Thorpe
>> Sent: Monday, 7 September 2009 2:16 p.m.
>> To: Richard Pyle; TAXACOM at mailman.nhm.ku.edu
>> Subject: RE: Why Australians are more real than Americans:
>> implications for taxonomy!
>>
>> Richard,
>>
>> I think the list can benefit from new angles on old and tired
>> debates, so I am replying to the list, despite your advice that this
>> will just bore people to death! :)
>>
>>> There are gaps at all scales.  To say that species boundaries are
>>> "real" is to say that the gaps that cluster around at the species
>>> level are somehow special -- more real than the gaps at higher or
>>> lower levels
>>
>> I agree! I wasn't trying to imply that species level boundaries are
>> any more or less "real" than any other level can be, except that
>> lumping/splitting of genera, say, is more subjective than
>> lumping/splitting of species, at least if you follow a biological
>> species concept. The whole Hominidae could just as correctly be a
>> single genus, for example. Lumping/splitting species is a bigger can
>> of worms.
>>
>> I think I see where you are coming from: consider allopatric
>> populations which differ only slightly (=very small gaps). Are they
>> the same species? Well, there is a determinate answer (independent
>> of us)  if you follow a biological species concept, it is just that
>> the answer can perhaps only be guessed at, and never known for sure.
>> The nitty gritty now becomes clear: if you follow a morphological
>> species concept, then ought ANY consistent gaps be species
>> distinctions, or is there room for subjective choice regarding how
>> much of a gap is required?
>>
>> Thought experiment: imagine that all the species out there look the
>> same as they actually do, but they don't breed, they just exist! So,
>> no chance of a biological species concept. Could we still do
>> meaningful (descriptive) taxonomy? The same patterns of morphology
>> and "gaps" would still be there to describe...
>>
>> I'm now less certain of my views, but one thing strikes me: if we
>> follow a morphological species concept, for it to make any coherent
>> sense, we might have to consider ANY consistent morphological gap to
>> be a species boundary! The only reason why we often do ignore such
>> small differences between allopatric populations is that we consider
>> the gaps to be insufficient to produce reproductive isolation...
>>
>> The reason why all this is relevant at present, has to do with the
>> correct understanding of "identification" (at least at the species
>> level):
>> if you are right, then two identifiers can disagree PURELY
>> subjectively about the identity of a specimen - one of them can be
>> correct relative to his concept, and the other can also be correct
>> relative to the other's own concept. There would be no "fact of the
>> matter". In that case, an identification without specification of
>> the relevant taxon concept would be fairly meaningless.
>>
>> But, on my Australia analogy, to identify a specimen is to say that
>> a given land coordinate is part of Australia (forgetting all the
>> little inshore islands and Tasmania), and there is a fact of the
>> matter about this.
>>
>> So, it all seems to come down to which species concept is
>> used/best/true. The subjective view on species identification
>> presupposes a morphological species concept with subjective choice
>> on how wide the gaps need to be. On either a biological species
>> concept, or a "gap or no gap" morphological species concept, there
>> is only a single true species identity for any given specimen...
>>
>> Stephen
>> _______________________________________________
>>
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>
>
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Dr.B.J.Tindall
DSMZ-Deutsche Sammlung von Mikro-
organismen und Zellkulturen GmbH
Inhoffenstra├če 7B
38124 Braunschweig
Germany
Tel. ++49 531-2616-224
Fax  ++49 531-2616-418
http://www.dsmz.de
Director: Prof. Dr. Erko Stackebrandt
Local court: Braunschweig HRB 2570
Chairman of the management board: MR Dr. Axel Kollatschny

DSMZ - A member of the Leibniz Association (WGL)



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