[Taxacom] barcode of life

Richard Zander Richard.Zander at mobot.org
Sun Jul 4 11:27:12 CDT 2010


 


Well, Stephen, your note is particularly interesting. You are right
about the guiding (not fundamental but guiding) principle of order of
magnitude of differences of precedent is okay in absence of other info. 

 

On the other hand, you state: " It is an in principle refutable
hypothesis that they are distinct species. To call them subspecies would
be to postulate no such reproductive barriers, but rather just to name a
distinct population with its own "morphological flavour"
Well, answer me this: can you give me a percentage, any guess even, of
the percentage of species with KNOWN reproductive barriers compared to
those described on the basis of inferred reproductive barriers based on
morphological differences. I use morphological differences to infer
different evolutionary directions or just plain isolation that seems
ecologically significant, or that does not match the kind of variation
found within similar species. I don't use inferred reproductive
isolation myself. For birds and other well-known, well-studied
organisms, it's doubtless okay, but for a vast group of organisms
reproductive isolation is either unknowable, or doubtless only partial,
or not applicable. I think across-the-board defense of reproductive
isolation for all organisms, or even just for all sexual organisms
(Mayr), is overdetermination and downright metaphysical.

*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
*****************************

________________________________

From: Stephen Thorpe [mailto:stephen_thorpe at yahoo.co.nz] 
Sent: Saturday, July 03, 2010 9:04 PM
To: Richard Zander; Robin Leech; dipteryx at freeler.nl;
taxacom at mailman.nhm.ku.edu; Steve Manning
Subject: Re: [Taxacom] barcode of life

 

Richard,

As someone once said "science isn't an exact science", and it is very
true in the present context! I think that there are background
assumptions guiding taxonomists which cannot be rendered perfectly
precise, but which are nonetheless fundamental principles of taxonomy.
One such principle is that if the order of magnitude of some difference
between allopatric populations is on a par with accepted exemplars of
distinct species, then this is good evidence for the species distinction
in this case. In the case of Geodorcus sororum, the male morphology is
as different to that of G. capito as any two Geodorcus species are to
each other. It just happens to be the only difference between G. sororum
and G. capito. It is an in principle refutable hypothesis that they are
distinct species. To call them subspecies would be to postulate no such
reproductive barriers, but rather just to name a distinct population
with its own "morphological flavour" ...

Cheers,

Stephen

 

________________________________

From: Richard Zander <Richard.Zander at mobot.org>
To: Stephen Thorpe <stephen_thorpe at yahoo.co.nz>; Robin Leech
<releech at telusplanet.net>; dipteryx at freeler.nl;
taxacom at mailman.nhm.ku.edu; Steve Manning <sdmanning at asub.edu>
Sent: Sun, 4 July, 2010 4:10:05 AM
Subject: RE: [Taxacom] barcode of life




Cryptic species, Stephen, we are talking about those without "are
significant morphological (genitalic), behavioural, and/or genetic
differences of the order that is normally taken to be indicative of
reproductive isolation and therefore species delimitation"

 

I do not know how much or if at all differences in non-coding traits
affect reproductive isolation. How much difference in non-coding traits
interfer with reproduction?

R.

*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis , MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
*****************************

________________________________

From: Stephen Thorpe [mailto:stephen_thorpe at yahoo.co.nz] 
Sent: Friday, July 02, 2010 6:43 PM
To: Richard Zander ; Robin Leech; dipteryx at freeler.nl;
taxacom at mailman.nhm.ku.edu; Steve Manning
Subject: Re: [Taxacom] barcode of life

 

> Sounds arbitrary, axiomatic, and true-believerish
>Sympatric cryptic species are a special case for which each instance
must be examined

 

Sounds rather ad hoc-ish to me!

 

>Reproductive isolation of populations is common, yet the populations
are also still the same species
Reproductive isolation in the sense that the populations WOULDN'T
interbreed freely IF they were to come together under natural conditions
- the standard zoology 101 definition of biological species (at least
when I went to school)

 

Please give me an example of two populations which are the same species
even though there are significant morphological (genitalic),
behavioural, and/or genetic differences of the order that is normally
taken to be indicative of reproductive isolation and therefore species
delimitation? If I understand them correctly, even the molecular
taxonomists are looking for genetic differences of sufficient magnitude
to indicate reproductive isolation - they just think that morphological
differences are only one of several ways that can lead to such
reproductive isolation ...

 

Stephen

 

________________________________

From: Richard Zander <Richard.Zander at mobot.org>
To: Stephen Thorpe <stephen_thorpe at yahoo.co.nz>; Robin Leech
<releech at telusplanet.net>; dipteryx at freeler.nl;
taxacom at mailman.nhm.ku.edu; Steve Manning <sdmanning at asub.edu>
Sent: Sat, 3 July, 2010 4:00:13 AM
Subject: RE: [Taxacom] barcode of life

"Right" lines, Stephen? Sounds arbitrary, axiomatic, and
true-believerish. Reproductive isolation of populations is common, yet
the populations are also still the same species. Or is there a
distinguishing metaphysical dimension I cannot see? Boundaries for
higher taxa are sometimes arbitrary but more often refer to real
clusters of species. Even Aristotle, so I am told, distinguished species
and genera.

No, the boundaries must not delimit (strict) monophyletic groups.
Certainly not. Absolutely, irrefragibly not. Paraphyletic and
polyphyletic groups may signal shared ancestry deep in the tree, and
require discursive reasoning and evolutionary theory, and facts not in
the data set to figure out what the data signify. 

Sympatric cryptic species are a special case for which each instance
must be examined. 



*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis , MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
*****************************

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Stephen Thorpe
Sent: Thursday, July 01, 2010 5:32 PM
To: Robin Leech; dipteryx at freeler.nl; taxacom at mailman.nhm.ku.edu; Steve
Manning
Subject: Re: [Taxacom] barcode of life

what Robin says is more or less along the right lines, but to be a
trifle clearer:

species boundaries delimit reproductive isolation (which is not to say
that it is black and white, all or nothing) and to that extent are
"real"

boundaries for higher taxa are arbitrary/subjective/conventional, and
delimit nothing "real" in the world (which is not to say that the taxa
themselves are purely arbitrary/subjective/conventional, only that their
boundaries are - the boundaries must delimit monophyletic groups)

of course, the requirement of reproductive isolation is implicit in just
about every notion of species - what sense can be made of sympatric
cryptic species if they freely interbreed? Total nonsense!


 


 




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