What's a subspecies was: Species Concept Question

[Richard Pyle]

> And although the vrolikii population is less numerous than the flavissima
> population, I assume that it is only uncommon (not threatened or
endangered),
> so I still think the 2 subspecies solution would be best.

If I indicated that vrolikii is less numerous, then I apologize for
miscommunicating.  They are actually both about equally abundant in areas
where they each live, and their range of distribution is roughly the same as
well (if measured as a function of appropriate habitat).

See:
http://www2.bishopmuseum.org/PBS/images/flavissima.gif

(Fig. 4 of 3. Pyle, R.L. and J.E. Randall. 1994. A review of hybridization
in marine angelfishes (Perciformes: Pomacanthidae). Envirnmental Biology of
Fishes 41: 127-145.)

> I would be interested to know why you chose to continue recognizing them
> as two separate species.

First and foremost:  nomenclatural stability.  As I say, these names have
been extraordinarily stable in their century-and-a-half of existence, and
show up in numerous popular field guides, aquarium books, magazine articles,
etc., etc.  To regard them as subspecies now would just cause a lot of folks
to scratch their heads.  The hybridization zone is also well-documented, and
most of the world (taxonomists, other scientists, layfolk) think of this
zone as a hybrid swarm.  So...there really is no new information here upon
which to base a change in nomenclature.  All I would be doing is imposing my
own pet philosophy about the function of trinomials on the rest of the
world.  My hunch is that the rest of the world wouldn't be very happy if I
did this.  More fundamentally, I'm not sure that communication would be
enhanced (if anything, it would be somewhat disrupted).

Maybe some day, with a massive review of all similar cases in reef fishes
(which Jack Randall and I are semi-contemplating as part of a general paper
describing our own perspective of the value & utility of trinomials in reef
fishes), they could all be re-defined with trinomial nomenclature at once.
But to do it only for this and a few other isolated cases would not, in my
opinion, enhance the process of communication among biologists.

Furthermore, as you might gather from the map image linked above, the story
is a bit more complex.  There is another species involved:

C. eibli
http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=1207236279

that forms hybrids with a truely bizarre (but not altogether unprecedented)
"remnant" population of flavissima in the eastern Indian Ocean. That
population has a few distinct color differences from the Pacific flavissima;
primarly that it lacks the blue ring arounf the eye, and has a distinct
black bare at the posterior edge of the operculum.  I do have a photo of the
hybrid:

http://www2.bishopmuseum.org/PBS/images/JER/detail.asp?ID=376948780

Ignore the locality of "Hawaii" -- this fish was collected at
Cocos-Keeling -- which is sort of interesting, in that I don't believe that
C. eibli has ever been recorded there.

Moreover, there is another population in this complex at Rowley Shoals,
which is as yet un-named, which is every bit as distinct from the others as
the others are from each other (and, indeed, may prove to be the other
parent of the above hybrid, rather than "true" eibli).

And it gets even more complex, in that we can't rule out the possibility
that Indian Ocean "flavissima" are non-monophyletic with the Pacific forms,
with respect to the other two species.  In other words, we can't discount
the hypothesis that the Indian "flavissima" arose as a xanthic morph
population entirely independantly of the Pacific "flavissima" (if, indeed,
this is how they arose), and thus may represent convergence in color.

As you can see, the entire picture is a bit of a mess (a PhD thesis in the
making, really).  So all I wanted to focus on (for now) was the two
morphotypes vrolikii and Pacific flavissima, with their hybrid zones.

Perhaps more than you wanted to know....  :-)

But the point is, absent any real new information about the evolutionary
relationships of these two morphotypes, I decided that my bias in favor of
nomenclatural stability superceded my bias towards how trinomials should be
implemented in reef fishes.

> Although the change would have raised some eyebrows or even some protests,
> I still don't think it would have been that destabilizing.

Maybe not -- but I also have to ask, "what's wrong with the status quo?".
If the only problem is that we must depart from a strict biological species
concept (i.e., allowing for fertile hybrids between two forms tagged as
"species"); well, I don't see that as being as big a problem as we would
have to deal with if ALL cases of fertile hybrids forced us to treat the
parents as conspeciefics (with or without trinomial distinction).

> Although I do understand the temptation to follow historical
"inertia"/"bias"
> in the interests of stability, new information does require some level of
> instability

I guess my point here is that there really is no "new" information.  We've
known about the hybrid swarm since the 70's yet nobody has been tempted to
use this information to synonymize the two species.  What, really, would I
(or the taxonomic community at large, or the lay community at larger still)
gain if I were to nomenclaturally "rock the boat"?

> (but I believe the subspecies designation would minimize instability
> and/or confusion in this case).

I agree -- and more significantly, I think this case exemplifies my own
preferred definition for when trinomials should be invoked.  But I would
like to gain some real new information (e.g., molecular data from the study
that we are ramping up for) upon which to base the nomenclatural change.

> Also, I would be very interested to know what species (or species group)
> is thought be most closely related to the flavissima-vrolikii group
> (whether or not the latter is regarded as two species or one).

There are five distinct morphotypes in the complex, and no obvious
sister-complex outside of this complex.  They include:

FP=Pacific flavissima
FI=Indian Ocean flavissima
VR=vrolikii
EB=eibli
RS=Rowley Shoals population (don't have a web photo of that, but it appears
in Debelius et al. 2003).

As far as I can tell, the only measurable morphological differences among
these forms is color (remove the color, and they'd be essentially
indistinguishable morphologically).

Based only on color, one might speculate something like:

((FP,FI) ((RS,EB) VR))

If you consider also biogeographic distribution, you might prefer something
like:

((RS,EB) (VR (FP,FI)))

But we can't discount the possibilities of:

(((RS, FI) EB) (VR, FP))

or

(((EB, FI) RS) (VR, FP))

or

(((RS, EB) FI) (VR, FP))

So...maybe when someone sorts all of this out with molecular data -- as
we're gearing up to do -- then we might have a solid basis for disrupting
traditional nomenclature.

Aloha,
Rich

=======================================================
Richard L. Pyle, PhD
Ichthyology, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at bishopmuseum.org
http://www.bishopmuseum.org/bishop/HBS/pylerichard.html