Hi Wayne,
Thank you for the insightful, thoughtful and clear discussion regarding
alternatives to the Biological Species Concept (BCS) such as the
Phylogenetic Species Concept (PSC) that you describe. Well said. As you
are likely aware, there are other options such as Isolation species
Concept, Ecological Species Concept, Cohesion Species Concept, etc. It is
messy but as Lars stated ...."real progress is being made in taxonomy, and
at an accelerating rate". The world of genomics and DNA is shining the
light in many dark corners.
For sure, this is a debatable and mushy subject, defining what is a
species, and I respect the job and challenge the AOU Checklist committee
has in trying to sort this out. These are intelligent and experienced
people making judgement calls based on the best information available.
Depending on the species concept you prefer, there remains some room for
debate about the decisions made on splitting and lumping. This is by no
means a perfect and indisputable science.
Charles Darwin stated ...."Those who make many species are the splitters,
and those who make few are the lumpers". As you admitted, you tend to be a
splitter and I would admit I tend to be a lumper. There is remarkable
genetic variation within every species and selection pressures create
diversity. Assortative mating is a type of selection pressure and is
likely present in all species. Mating choices are often made related to
the most colorful, the strongest, the loudest, the biggest, etc. But why
would assortative mating be a reason to split the Northern Oriole again?
If a collection of female Baltimore and male Bullock's orioles were placed
in a large aviary, would they readily breed and hybridize? And
subsequently, would they have progeny that continued to successfully
hybridize and blend their respective gene pools. Or would the original
individuals just eventually die of old age, with a few if any infertile
offspring? BCS would provide a species answer here. Of course, it
becomes a debate again of one's preference of species concept.
I wish there was another taxonomic layer below species that wasn't
"sub-species", which sounds so ... ho-hum. Morphological or vocalization
differences just doesn't feel like enough evidence to split species, but
inability to successfully hybridize does. And believe me, I have no clue
whether California and Woodhouse's Scrub-Jays successfully hybridize out on
the open range. Probably they don't!
Anyway, good stuff! Please enjoy birding whether you are a splitter or
lumper.
Roger Freeman
On Fri, Jul 8, 2016 at 9:29 AM, <whoffman@xxxxxxxx> wrote:
Hi, Roger -
In the 1980s-1990s there was a major challenge to the use of the
Biological Species Concept (BSC) by the "Phylogenetic Species Concept"
(PSC). I won't give a detailed description of the PSC, but note that
under it there would be a lot more splitting, and hybridization would be
considered less of an issue.
In about 1998 Ned Johnson of the Museum of Comparative Zoology, UC
Berkeley, and co-authors published a paper describing an updated BSC. At
that time the AOU Checklist Committee endorsed the new and improved BSC,
and that has largely informed the committee's decision-making since then.
The BSC was first formulated by Ernst Mayr and colleagues in the 1930s, and
a lot has been learned about population biology and genetics since, so an
update made sense.
Under the new BSC, hybridization is considered less indicative that two
populations are the same species than previously. The important point to
understand here is that hybridization should not be treated as a True/False
question. A whole lot of grey exists between "never hybridizes" and
"hybridizes freely." Numerous examples are available of populations that
hybridize sporadically, but where most individuals mate with with "their
own kind."
So under the new and improved BSC, populations that are mostly allopatric
(non-overlapping ranges) but occasionally meet, with some hybridization can
still be considered species. Also populations that overlap with quite a
bit of hybridization, but with evidence that the hybrid offspring are less
viable or selected against, can be considered species.
In general, if hybridization is not so frequent that it forms a large and
expanding "hybrid swarm" species status may be maintained. Several "kinds"
of birds have eastern and western forms that meet on the Great Plains, with
at least some hybridization. One of these, Northern Flicker, was lumped
because hybrids are very widespread, and not much evidence exists that
birds in the contact zone are very choosy. Several others,
Rose-breasted/Black-headed grosbeaks, Indigo/Lazuli buntings, etc. have
been maintained as separate species because the hybridization is fairly
sporadic. Baltimore/Bullock's orioles were first lumped into "Northern
Orioles", then re-split, when more evidence of assortative mating
(discrimination, or "choosiness") was discovered.
In a few cases (e,g, Tufted/Black-crested titmice) two wide-spread "pure"
populations are connected by a narrow band with lots of hybrids but the
band remains narrow, and the hybrids do not seem to be dispersing out into
the "pure" main populations. These are now considered separate species.
Townsend's/Hermit warblers may have a similar dynamic.
So, 2 take-home messages:
First, those who make the rules (AOU Checklist Committee) are comfortable
with giving species status to populations that sometimes hybridize, but
mostly maintain separate identities.
Second, "Species" are in part human constructs that work well to describe
the diversity of life in a majority of cases, but examples are not rare
where nature is messier, i.e. less divisible into discrete units. In those
cases, a lot of judgement is required and the best we can hope for, is that
the decisions are made somewhat consistently. The AOU Checklist Committee
seems to be trying to be consistent.
Finally, I want to say that I tend toward being a "splitter" because the
more "kinds" there are to look for, the more of a challenge it is. To me,
it is an improvement that when I am in SE Oregon, I cannot just say "Scrub
Jay" and move on. "Scrub Jay" has become a category that deserves a closer
examination, and that is a good thing.
Wayne
------------------------------
*From: *"roger freeman" <carrotguy55@xxxxxxxxx>
*To: *"obol" <obol@xxxxxxxxxxxxx>
*Sent: *Thursday, July 7, 2016 9:02:46 PM
*Subject: *[obol] Western Scrub-Jay split and Speciation
Cool thread about the splitting of our beloved WESTERN SCRUB-JAY into two
different species.
I am fascinated by the discussions that relate to splitting or lumping
species of plants or animals. Or about hybrids that occur between
"different" recognized species I read a lot of the manuscript that Bob
Archer provided earlier .... here it is again.
http://www.aoucospubs.org/doi/pdf/10.1642/AUK-16-77.1
Several times the evidence for making the species split is given as ....
"Differences in morphology, ecology, vocalizations", etc .... But there
appears to be little/no evidence or mention of the inability to
hybridize/mate and generate normal and fertile offspring/progeny that can
successfully mate again.
Even though there is some debate about what constitutes speciation, "the
biological species concept" would state simply that .... If two organisms
(plant/animal/fungi) can mate and produce fertile offspring, then they are
the same species. Granted this can be harder to "check" in animals vs
plants. Physical isolation for centuries can cause changes in morphology,
but it doesn't necessarily change speciation. With genomic technology
available today, it is quite simple to show clear significant differences
in DNA sequences between very different individuals of the same species.
The use of sub-species classification is commonly used, and provides a
good option for where there are differences in morphology, vocalizations
or ecology, but mating status is unknown. Domestic dog used to
be considered a different species than wolves, but that has recently been
revised so that domestic dog is now a sub-species of wolf due to the fact
that they can successfully interbreed and dogs are selected descendants
from wolves.
Lumping or splitting is an ongoing debate in the taxonomic world.
Good birding!
Roger Freeman
