Dear all,
I guess Wim Vader is making a very good point about the fact that people
shouldn't shoot the messenger, as is so often done with respect to
phylogeneticists constributing to our knowledge of bird taxonomy.
Just as it is wrong to lose all scepticism and blindly believe in anything
that bears the air of scientific authority, it is equally wrong to throw out
the baby with the bathwater by downplaying the immense relevance of
phylogenetics to the topic of avian taxonomy.
Our traditional classification of birds is the product of hundreds of years
of painstaking work on the morphology of (mostly) museum specimens, but even
that development had to come to a relative halt in the lull of the early
20th century, because there is just so many times you can re-examine the
same morphological characters. With the molecular revolution of the 90s, all
of a sudden evolutionists had new and (in many respects) more powerful tools
to look at the interrelationships between individuals, populations, races,
species and genera.
In response to Andrew's message, I think a 648 bp stretch of COI tells us a
great deal about the bird it came from, and it can probably nail it down to
species level in 95% of all cases. Whether that 648bp stretch is sufficient
on its own to split one population off as a different species is a matter of
dispute (my own opinion would mostly be No), but as Wim pointed out, the
authors of the Barcoding paper never made such bold claims explicitly, so
please don't shoot the messenger!
As a response to Dave's message, there are indeed many examples for the
careless misuse of genetic divergences as a tool for splitting, with
arbitrary cut-off figures and without any due consideration to the caveats
of this method. However, there are even more examples where genetic
divergences have been used properly and calibrated against appropriate
yardstick values to infer the potential species status of two allopatric
(=geographically non-overlapping) populations. So here again, it is
important not to make the impression as if you wanted to brand an entire
line of enquiry as nonsense (though I am sure you didn't want to suggest
that, Dave...)
Happy birding everyone
Frank
------------------------
Frank Rheindt
Genetics Department
University of Melbourne
From: Andrew Hobbs <>
To: Birding Aus <>
Subject: Re: [Birding-Aus] DNA based lumps, splits and IDs
Date: Fri, 23 Feb 2007 18:05:51 +0900
As a molecular genetecist, I would say that relying on 648 bp of
mitochondrial sequence is about as good at distinguishing species as
sending out a beginner birder and asking whether they think they represent
two species.
Cheers
Andrew
Dave Torr wrote:
Thanks Frank - that is very clear. So the publicity is about as justified
as
(say) a new fig parrot is?
Seriously I have always had doubts (as a non biologist) about some of this
DNA stuff - I attempted to read one paper and the author seemed to be
saying
that if the difference in the small part of the DNA he had studied was
more
than "x" % then he would declare the beasts to be separate species. The
choice of "x" seemed totally arbitrary.
Still - I guess as long as taxonomists can generate new ways of looking at
the world we will never be short of the need to buy new bird books and
update our "life lists"
On 23/02/07, Frank Rheindt <> wrote:
David (and others),
trying to keep it short:
1.) These DNA barcode people are just looking at one single gene (COI),
which happens to be one out of three dozen genes on the mitochondrion (a
tiny cell organelle). In the nucleus of each cell, there are millions and
millions more genes, many of which are responsible for the appearance of
an
organism. So it all depends on what you really want to do: If you were
looking at a gene that codes for the colour of a duck's wing speculum,
you
bet there would be huge differences between Blue-winged and Cinnamon
Teal.
However, phylogeneticists try to look at neutral genes that don't have
anything to do with what an organism looks like, to avoid circularity.
2.) Barcoding is a nice tool to detect "suspects" for splitting/lumping,
but
in most cases more phylogenetic work will be necessary to corroborate the
split/lump. For example, let's take the case of those "species with
identical DNA": First of all, never say they have identical DNA, but say
something along the lines of "...they have an identical sequence in their
COI gene..." (which is less than a millionth of their total DNA).
Secondly,
the reason for having an identical COI sequence could be manifold, and
could
involve things such as ancient hybridization events (during which one
species' COI gene "invaded" that of the other) - this is called
mitochondrial introgression and is fairly common in birds. So those
species
can still be viable and valid species despite that finding! (A similar
case
in Australian birds involves White-browed and Masked Woodswallows, which
have identical mitochondrial DNA).
Bottomline: DNA barcoding is a nice tool to whet our appetites, but in
each
case, a split or lump requires subsequent follow-up studies to
corroborate
the case.
Cheers
Frank
>From: "Dave Torr" <>
>To: "L&L Knight" <>
>CC: Birding Aus <>
>Subject: Re: [Birding-Aus] DNA based lumps, splits and IDs
>Date: Fri, 23 Feb 2007 15:30:04 +1100
>
>Maybe I'm missing something (and I'm no expert on DNA!). The reference
on
>"splits" shows a number of what I have always thought of as "good"
species
>anyway, with no indication of what they have been split from (or what
has
>been split from them).
>
>And the DNA lumps shows Blue-winged Teal and Cinnamon Teal to be 100%
>similar - yet visually at least they are very different...... Since as
a
>"layman" I assumed DNA controlled the appearance of an animal how can
this
>be the case?
>
>Please excuse the ignorance but I would love someone to explain in
simple
>terms.....
>
><>
>>
>>
>>< DNA splits >
>>
>>http://www.eurekalert.org/multimedia/pub/3183.php?from=90533
>>
>>Unique DNA barcodes for provisional new bird species were obtained
from
>>these look-alike specimens.
>>
>>
>>< DNA lumps>
>>
>>http://www.eurekalert.org/multimedia/pub/3185.php?from=90533
>>
>>These groups of bird species were shown to have virtually identical
DNA.
>>
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