Dear Birdingaussers,
Following is the recent debate on BirdChat on species, in which I
participated, and nearly got kicked off for flaming. Touchy egos some
Americans, and they take themselves so seriously!
Basically I think Andrew Taylor is correct in his recent posting to
Birding-Aus: the species of the RAOU checklist is what the authors
perceive as a species and has nothing to do with definitions or
empiricism. I do not disagree with this as long as it is acknowledged.
I have been an advocate for designer-taxonomies for birding clients for
over twenty years. However, all birders ever receive is
designer-taxonomies for the authors of a particular checklist then told
to "shut up" because the classifications have been produced by science.
As you can see, I have several buttons you can push in this type of
debate. But don't! I don't even know why I am posting this. Perhaps I am
under a glamour..........
In what follows, Futuyma's summary is excellent. He is one of the last
students of Ernest Mayr, the ornithologist and evolutionary theorist. It
begins with my subsequent attempt to bring Futuyama up to date with the
RCS. However, that is continuing in another medium.
Hope this all helps. If it doesn't, Robert Quinan don't ask the question
again or you will be burnt at the stake!
Best wishes
Glen Ingram
Brisbane, Australia
P.S. Would the lady that contacted Michelle Ryan to write a Regent
Honeyeater article please contact her again: 07 38407602,
Your address has been lost in a forced office
move.
---------------------------
> From: Glen Ingram <>
> To: Birdchat <>
> Subject: Last post
> Date: Wednesday, 28 May 1997 15:18
>
> Dear Chatters,
> Doug Futuyma's posting was worth the flaming trouble. I mean one has
to
> usually beg to get that quality information anytime, let alone have it
come
> into our living rooms (for me it is into my bed). Actually we should
thank
> Diane Porter, although one email to me said God was going to get her
for
> starting all this again.
>
> The only thing I would add to Futuyma's dissertation is more
information on
> the Recognition Concept of Species. They say Hugh Paterson, the
originator
> of the RCS, took huge chunks out of Futuyma's book with his teeth
when it
> first came out.
>
> Firstly, to the Phylogenetic Species Concept. I now believe the PSC is
not
> a definition: it is a wish list. What convinced me was an email from a
> certain taxonomist who said "I had got it wrong": the PSC is coming to
> birdwatching NOT because it is being scientifically-imposed, but
because
> amateurs are imposing it: they think they are going to get more
species out
> of it! Which is fine. As a consumers, we have every right to ask for
> designer-taxonomies, but those who take the high moral ground and
invoke
> "science" for their choices are laying it on a bit thick. You only
need to
> invoke "the right to chose". And I am on your side and I will design
it for
> you.
>
> Futuyma said in his email:
> >
> > The "recognition concept", to which some chatters
> > have referred, is not substantially different from the BSC,
> > except that some of its advocates accept only behavioral
> > isolation, not hybrid sterility, as a basis for species
> > distinction. It has not been widely accepted.
> >
>
> Yes, it is similar to the BSC and I feel it is the only competitor as
> useful definitions go. However, he is just off centre. The RCS defines
a
> species as "bisexual organisms that share the same specific-mate
> recognition system". The similarity, I think, is because the two
concepts
> are the two, different sides of the same coin. One side = "isolation
and
> apartness" - the BSC, and the other = "recognition and coming
togetherness"
> - the RSC.
>
> I go back to you and that cow I mentioned in an earlier email. The
BSCers
> are more interested in what will happen if you have sex with that cow
(will
> there be no progeny or will your progeny be sterile? If so, you belong
to
> different species). The RCSers are more interested in why you chose to
have
> it off with the cow in the first place (because if you did, and you
are
> typical, there is no difference between you and your ilk and the cow.
They
> don't give a damn what happens to your baby: you are the same
species).
>
> That's it in a nutshell. BCS people study what keeps groups of
individuals
> apart. RCS people study what brings groups of individuals together.
> Semantics you think? No way. The RCS lumps as a program and the BSC
splits.
> Which leads to, unfortunately, the biggest hole in the BSC: hybrid
> sterility.
>
> Darwin said it, Paterson said it, and trains of other evolutionists
have
> said it for nearly 1.5 centuries: hybrid sterility cannot be selected
for
> by natural selection. How can you select for having no offspring?
There
> are NO offspring to pass on the no-offspring trait. Thus if species
are
> results of evolution, hybrid-sterility is not one of their traits.
QED.
>
> That is why the RCS lumps compared to the BSC. If applied to present
> checklists, we would lose all birds that recognize each other as mates
and
> hybridize. Technically, the definition would have another far-reaching
> application: birds that recognize each other as mates but have sterile
> young would get lumped too: but I cannot think of an example.
>
.........................................
> Best wishes to you all and signing off
>
> Dr Glen Ingram,
> Senior Curator,
> Department of Vertebrates,
> Queensland Museum,
> BRISBANE AUSTRALIA
>
>
> "Evolution and the Recognition Concept of Species. Collected
Writings.
> Hugh E.H. Paterson." Edited by F. McEvey.
>
----------------------------------------------------------------
> From: Doug Futuyma <>
> To:
> Subject: [BIRDCHAT] what is a species?
> Date: Wednesday, 28 May 1997 5:35
>
> Chatters,
>
> I'm prompted by the extensive (and probably unending)
discussion
> of species to add a few words. I'm professionally involved with the
> subject, both in my research on insects and in covering it for the
> revised edition of my textbook on evolutionary biology, nearing
completion.
>
> A definition is a convention, so there are no scientifically
> "correct" definitions, only those that are more or less useful - which
> depends on the intended purpose. The purposes of a species concept
differ
> to some extent between biologists who study evolutionary processes and
> those who study evolutionary history and are concerned chiefly with
> classification and phylogenetic relationships among groups of
organisms.
>
> Mayr's biological species concept (BSC) continues to be
favored by
> most process-oriented evolutionary biologists (including me). It
defines
> a species as a population or group of populations that is actually or
> potentially reproductively isolated from other such groups.
> "Reproductively isolated" means that two groups do not substantially
> exchange genes in nature, because of **biological** differences that
> prevent gene exchange, such as behavioral isolation (they don't mate
even
> if they encounter each other) or sterility of hybrids. Mere
geographic
> isolation does not define groups as species. This raises the great
> problem of whether we suppose such groups are *potentially*
reproductively
> isolated, a problem I'll return to.
>
> The "recognition concept", to which some chatters have
referred,
> is not substantially different from the BSC, except that some of
> its advocates accept only behavioral isolation, not hybrid sterility,
as a
> basis for species distinction. It has not been widely accepted.
>
> The major current contenders with the BSC are several versions
of
> a "phylogenetic species concept" (PSC), which are gaining quite a few
> adherents among systematists. Some (e.g., ornithologist Joel
Cracraft)
> define a phylogenetic species as a *diagnosable* population or group
of
> populations "among which there is a pattern of ancestry and descent"
> (i.e., gene transmission across generations). Under this definition,
any
> population in which most members share a distinctive feature of any
kind
> that distinguishes it from other populations is a species. It could
be a
> single morphological feature, a single base-pair difference in DNA,
> or whatever. Advocates of the PSC argue that this definition
recognizes
> the **historical products** of evolution (i.e., genetically divergent
> populations), rather than the future evolutionary potential of
populations
> (i.e., whether or not they will some day interbreed), which is often
> unknowable. The emphasis here, then, is on what the history of
evolution
> has produced, rather than on the process of divergent evolution as
such.
>
> The difference between these concepts of species stems from a
> philosophical difference in what "work" a species concept is supposed
to
> do - and since the advocates want it to do different work, they want
> different definitions. For birders, the main consequence is that
> the number of named species (taxa with different binomial names) will
> increase substantially if taxonomists incline toward the PSC and if
> organizations such as the AOU follow their revisions. There are two
> major contexts in which the species recognized under the PSC will
differ
> from those recognized under the BSC.
>
> One situation, of which we know a few examples and will
> probably discover many more, is when a biological species, A, is found
> (usually by molecular data) to be phylogenetically more closely
related
> to certain populations of biological species B (say B1) than to
> other populations of B (say B2). That is, A and B1 stem from a more
> recent common ancestor than B1 and B2. For instance, mitochondrial
DNA
> analysis by John Avise et al. suggests that the American Black Duck is
> more closely related to American populations of the Mallard than the
> American and Eurasian populations of Mallard are to each other. This
can
> be determined only if there are diagnosable differences between
American
> and Eurasian Mallards, of course. Under the PSC, the American and
> Eurasian Mallards would be named as different species (even if they
> potentially interbreed - as we might find them to do freely in a zoo -
> and even if they actually interbreed somewhere, such as perhaps in
> western Alaska).
>
> The much more common situation is found with allopatric
> populations. For a process-oriented evolutionary biologist, potential
> interbreeding is interesting (after all, geographic ranges change, and
> geographically isolated forms may meet, with or without human
> assistance), but unfortunately the potential for interbreeding is
usually
> very hard to assess. There is no good way to *apply* the BSC in such
> cases, even though it *conceptually* embraces such situations. Thus,
> many allopatric forms are named as subspecies, many are named as
species
> if they show more pronounced differences, many have wandered between
> subspecific and specific status over the years, and there is no way to
> say which is right. (Charles Sibley, in the current Birding and
earlier,
> calls them "allospecies," which is fine; unfortunately, you can't
tell
> from a binomial whether a form is an allospecies or a "good"
biological
> species.)
>
> For advocates of the PSC, allopatric populations aren't a
problem:
> if you can find a difference between them, no matter how subtle, call
them
> species. Rigorous application of the PSC will *easily* double the
number
> of bird species; a very large fraction of current subspecies will
assume
> species status, and many populations that don't differ in morphology
but
> which do show molecular differences will be named as species. This
may be
> a logical consequence of a perfectly defensible species concept, but
it
> may well prove burdensome (especially for birders who already fret
about
> distinguishing Gray-cheeked from Bicknell's Thrushes, which at least
have
> some field characters). Even the concept of subspecies has long been
> criticized by some biologists, such as the paleontologist/evolutionary
> biologist George Gaylord Simpson, who wrote in Principles of Animal
> Taxonomy (1961), "The single species of pocket gophers Thomomys
umbrinus
> has 213 currently recognized and named 'subspecies' in southwestern
United
> States and northern Mexico, and those who enjoy that game may well go
on
> until every little colony of those gophers sports its own Linnaean
name."
> I hope "species" don't come to suffer such scorn.
>
> Molecular data play a big role in modern systematics, and
there
> seems to be some confusion among some birders on what such data tell
us
> about species status. First, we have to distinguish the use of such
data
> (or any data) in inferring phylogenetic relationships among organisms
> (i.e., which populations or species have more recent versus more
ancient
> common ancestors) from the role such data may play in diagnosing
> populations as being different species or not. DNA data are
exceedingly
> useful in phylogenetic analysis; they may or may not be useful in
> diagnosing species. Whether or not they are depends on whether the
> populations are allopatric or are in contact with each other.
>
> Before getting into that, I have to note that whether the DNA
used
> for study is an adaptively important gene or is silent, noncoding,
> so-called "junk" DNA is irrelevant. The DNA variations are used as
> **markers** (indicators) for the degree to which genes in general are
> being exchanged between populations (if the populations are in
contact),
> or are used as an index of the overall degree of genetic divergence, a
> rough index of how long it has been since the populations ceased
> exchanging genes (whether due to geographic isolation or to biological
> isolating barriers).
>
> A DNA difference that consistently distinguishes two
populations
> will be grounds for recognzing them as species under the PSC - but so
> would a morphological difference. The amount of difference in DNA
> sequence is likely *not* to be a good guide to whether or not the
> populations would potentially interbreed, so it doesn't much help in
> naming allopatric populations as species if one uses the BSC. In the
> Great Lakes of eastern Africa, for example, there are many sympatric,
> clearly different biological species of cichlid fishes that differ in
> morphology, behavior, and ecology, but can't be distinguished by the
DNA
> sequences that have been examined so far. Conversely, geographic
> populations that do freely interbreed where they abut each other
commonly
> show substantial differences in at least the proportions of different
DNA
> variants (human populations are a clear example). So the test cases
in
> which we do know about reproductive isolation tell us that we can't
judge
> potential reproductive isolation from DNA in the allopatric cases.
>
> The situation is different if two populations are sympatric or
> paraptric (have abutting ranges). Molecular markers can provide a
better
> indicator than morphological features to quantify the amount of
> interbreeding (gene exchange) between sympatric forms (e.g., work by
Gill
> and others on Blue-winged and Golden-winged Warblers). For parapatric
> forms, such as Baltimore and Bullock's Orioles, DNA markers can
provide an
> indication of whether there is no gene exchange, or a little, or a
lot.
> If the DNA variant characteristic of each such form penetrates at low
> frequency only a short way into the range of the other, it is likely
that
> something, such as low reproductive success of hybrids, is preventing
free
> genetic interchange. (At least for the genes examined; other genes
can
> well show different patterns. This is a very complex subject.) If
there
> is a very broad "hybrid zone," with each form's distinctive DNA
variants
> penetrating at low frequency far into the other's range, there are
> probably weak barriers to interbreeding, if any, and an advocate of
the
> BSC would be inclined to name subspecies rather than species (e.g.,
> "Yellow-shafted" and "Red-shafted" Northern Flickers). But the
*pattern*
> of the clines (frequency changes) in the molecular markers is what
makes
> the difference. The mere fact of an average difference means little.
> Thus, if Plain Titmouse populations west and east of the Sierras
differ in
> DNA (see DeBenedictis's Gleanings in most recent Birding), that only
means
> that those populations diverged while formerly isolated, and perhaps
don't
> disperse freely enough across the Sierras to rapidly homogenize their
gene
> pools - it doesn't necessarily mean that they are reproductively
isolated
> and will continue to diverge. (If differences in vocalizations,
behavior
> and ecology actually do reduce gene exchange, that's quite another
matter,
> which can be inferred either by studying those features themselves, or
by
> analyzing the pattern of geographic variation in molecular markers.)
>
>
> Well, that's probably more than enough. My main points are
that
> two species concepts that differ in philosophical foundation and in
> practice are now in use by researchers who have different research
goals;
> that allopatric forms usually can't be unambiguously defined as
species or
> not under the BSC; that the PSC, if widely applied, will also have
some
> awkward practical consequences; that DNA differences in themselves
will
> not generally help to decide the status of allopatric populations
under
> the BSC; and that the pattern of DNA differences, not the mere
existence
> of differences, is critical for establishing the status of parapatric
> hybridizing populations. I agree with most of what Sibley wrote in
his
> article on species in the current Birding, but wanted to expand on
some of
> his points.
>
>
> Doug Futuyma
> Dept. of Ecology and Evolution
> State University of New York
> Stony Brook, NY 11794-5245
>
>
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