What's a subspecies was: Species Concept Question

[Richard Pyle]

Thanks, Ken.

> I agree that subspecies can be viewed as incipient species.
> In your Centropyge example, the two populations may well be very
> far along the road to becoming separate species.  But if they
> freely interbreed where they come together, then they haven't
> crossed that line yet (and may never do so).  Changing weather
> patterns or other circumstances could cause the zone of hybridization
> to widen in the future, even to the point of making hybrids
> the "norm" and the original morphs becoming the outlying exceptions.

I fully agree.  Our crystal ball on the evolutionary future of these two
apparent "lineages" (vrolikii and flavissima) is clouded.  Maybe the hybrid
populations will remain proportionally small, and eventually either
"evaporate", or perhaps even form a third lineage of its own (don't get me
started).  Or, maybe the zone of intra-morphotype gene flow will expand
geographically (or, conversely, the populations not subject to
inter-morphotype gene flow may "evaporate"), and we'll be left with only a
single lineage derrived from both divergent morphotypes.  Or, maybe one of
the morphotypes will "evaporate", and the zone of hybridization will
eventually blend into the broader population of the extant morphotype (I'd
like to see *THAT* one represented on a cladogram....).

But the point is, we have good reason to believe that either scenario is
plausible; and therefore this fits my preferred definition of what the
subspecific epithet should be used for.

> To show that these two populations have not crossed the species line,
> I would call them Centropyge vrolikii vrolikii and Centropyge vrolikii
> flavissima.

Actually, C. flavissima (Cuvier in Cuvier & Valenciennes, 1831) has
nomenclatural priority over C. vrolikii (Bleeker, 1853); so the species
epithet for both would be "flavissima".

> Such a change may be "rocking the boat", but I don't consider it confusing
> or particularly disruptive.  It's just the least disruptive way to convey
> new information (they readily hybridize when they come together).

That's another part of my contorted question:  to what extent do we allow
nomenclatural history and stability to bias our decisions about current and
future nomenclature, in cases where "reasonable people might disagree"?  As
I said before, in the 150-year history of the species epithet "vrolikii", it
has never been treated as a junior synonym of "flavissima".  As popular
aquarium species, both have appeared in dozens (hundreds?) of popular books,
field guides, articles, etc.  Based on external appearances (within species
complexes of Centropyge, color is usually the only distinguishing
character), these two morphotypes are more dramatically different from each
other than many other sister-species pairs in the genus, such as the C.
acanthops / fisheri example I gave; or another species complex:

http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=-906582009
http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=831753142
http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=-1075464259
http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=1955815717
http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=1271064689

...in which hybridization is extremely rare or non-existant in areas of
sympatry.

So -- what sort of "consistency" are we trying to preserve in our
nomenclatural decisions?  Consistency based on evidence of propensity to
inter-breed in nature?  Consistency in how we as humans perceive the
organisms (by virtue of their distinguishing characteristics)? Consistency
in the way they have been nomenclaturally treated through history?

I know this is slipping into yet another flavor of the species concept
debate; but I really wanted to keep it focused more on patterns of
distribution of morphotypes, apparent hybrid zones, and general feelings
among the taxonomic community in how to use nomenclature to reflect the
apparent biological reality.

Getting back to my question above about historical nomenclature biasing
current nomenclatural decisions, my own feeling is that it should be very
low (compared to other influences on nomenclatureal decisions), but
non-zero.  There *is* value in preserving nomenclatural stability -- it's
just not clear how much this value measure up to other priorities in
nomenclature (reflecting inferred phylogenies; consistency of
implementation; as a means to catalog and quantify biodiversity; for issues
pertaining to conservation and endagered species; etc....)

> I'm speaking from a zoological perspective, and botanists may well
> take a different approach (plants are a whole different ball game
> when it comes to speciation, and asexual organisms are even more so).

Agreed -- and I would tend to lump Corals in with plants.

> P.S.  Keeping the two Centropyge populations as separate species is also
in line with
> the phylogenetic species concept.  Unfortunately this probably increases
the "bias"
> to keep them two full species, but I don't agree with that philosophy at
all.
> The subspecies concept gives us a means to add information into the
taxonomic name
> itself, and in the Centropyge example, no new names are needed (just a
change in rank).
> I would be hesitant to do this ONLY if Centropyge vrolikii flavissima is a
threatened
> or endangered population (a practical, political "bias"), but that doesn't
seem to
> be the case.

Yup, that's a good characterization of one aspect of my convoluted question:
how to balance the biases....

Aloha,
Rich