Last month [1] we belabored the definition of the word “subspecies,” using as our illustration Pleurocera catenaria dislocata, populations of which inhabit scattered small streams of the lower piedmont and coastal plain from Virginia to Georgia. And we warned, somewhat cryptically, about the “mischief” that might be precipitated should the concept of the subspecies be misunderstood, promising to develop that theme more fully this month. So this month let us return to our example of P. catenaria from the lower piedmont and plumb the taxonomic history of the nomen “dislocata” to substantially greater depth.
Edmond
Ravenel and L. A. Reeve probably ought to share joint credit for describing “Melania
dislocata,” but Ravenel (1834) is usually accorded the honor, by virtue of his
earlier publication date [2]. In either
case, the nomen “dislocata” was uniformly transmitted at the specific level by Tryon
and other 19th century authorities.
Based upon his keen appreciation for the plasticity of pleurocerid shell
morphology [3], however, Calvin Goodrich lowered the nomen to subspecific rank
under Goniobasis catenaria in 1942 [4].
Burch followed Goodrich, listing “Elimia catenaria dislocata” on page
132 of his 1989 “North American Freshwater Snails.”
I have
never cared for the American Fisheries Society’s “Common and Scientific Names
of Mollusks” book [5], the second edition of which was published in 1998. But the policy of Donna Turgeon and her
committee of 14 regarding the rank of subspecies was reasonable, and clearly
stated on page 15:
“Most subspecies are not suitable subjects for common names, but those forms that are so different in appearance as to be distinguished readily by lay people or for which a common name constitutes a significant aid in communication may merit separate names. There is a wide divergence of opinion concerning the criteria for recognition of subspecies. We have usually not named subspecies.”
So
for example, Burch (following Goodrich) recognized 50 distinct subspecific
nomina in the North American Pleuroceridae.
The great majority of these (44, to be exact) were not transferred by the
Turgeon/AFS committee to their 1998 book, and I am not complaining. Subspecies distinctions are subjective, and
often (as we have seen) without evolutionary basis, and if a committee of secondary
authorities simply resolves to lump all subspecific nomina under their parent
species as a matter of policy, fine. Turgeon and colleagues did, however, save one subspecific nomen in the
Pleuroceridae, Leptoxis crassa anthonyi, together with its cognate L. crassa crassa,
presumably because in the judgment of the committee, anthonyi is
“distinguishable readily by lay people.”
Okay, I won’t second-guess [6].
My problem
lies with the other five subspecific pleurocerid nomina, all in Burch’s concept
of the genus “Elimia.” In these five
cases, the Turgeon/AFS committee surreptitiously raised the subspecific nomina
of Goodrich/Burch to the species level: albanyensis, inclinans, vanhyningiana,
viennaensis, and (you guessed it) dislocata.
Subspecies are not species! Here in the modern era, specific nomina are
not somebody’s subjective opinion – they are testable hypothesis about the
reproductive relationships among sets of populations. What misanthrope thought he could
arbitrarily, high-handedly, without any explanation or indeed any notice,
promote five subspecific nomina [7], carrying with them no assumption of
heritability much less reproductive relationship, to the level of species [8]?
I
would confess that some personal irritation with the treatment given the
southeastern Pleuroceridae by the Turgeon/AFS committee at least partly motivated
several population genetic surveys I undertook subsequent to 1998. Last month we reviewed the 2002 paper I
published with A. J. Reed, reporting evidence for multiple independent origins
of the dislocata phenotype, strongly refuting the Turgeon/AFS surreptitious
elevation of dislocata to the species level [9]. And in 2011 I published a paper in AMB with
J.D. Robinson, synonymizing viennaensis and albanyensis back under Pleurocera
catenaria, again, and inclinans under Pleurocera floridensis, again [10]. One might hope that hard data published in
the peer-reviewed literature should trump the subterfuge of colleagues mired in
nineteenth-century typology. But no.
The
2013 AFS publication by Paul Johnson and committee [11] is 36 pages long, but
all one ever need examine is the single mysterious paragraph in which the
authors purport to describe their methodology, not saying more than they
say. In our post of 9Sept13 [12] we trained
the scientific equivalent of exegesis on the single sentence by which the
authors described their biogeographic methods, discovering something most foul
hidden underneath. Here we turn our attention
to the two sentences by which they described their taxonomic methods, as
follows:
“This list was derived from Turgeon et al. (1998) and updated with subsequently described species and systematic revisions. Subspecies are not recognized.”
I
initially interpreted the four-word rubric, “Subspecies are not recognized” to
mean that the Johnson/AFS Committee collapsed subspecific nomina under their
specific cognates. But upon closer study,
it would appear that Johnson and colleagues actually meant “Subspecies are raised
to the full species level.”
The
Johnson/AFS Committee also preserved the five subspecific nomina raised
surreptitiously to the species level by the Turgeon/AFS committee as species,
directly counter to research published between 1998 and 2013 in most cases. It is difficult to see how all fourteen of my
esteemed colleagues could have missed the 2002 paper I published in Malacologia
on the catenaria/dislocata pair or the 2011 paper that John Robinson and I
published in AMB on albanyensis, viennaensis and inclinans. So the implication must be that the Johnson/AFS
committee was aware that these nomina are only subspecifically distinct (at
best!) but elected to re-raise them back to the species level (again), under
the four-word rubric, “Subspecies are not recognized.” This is the down-up-down-up pattern I
illustrated at the top of this essay: subspecies prior to 1998, raised to
species level, demoted between 1998 and 2013, then raised a second time.
There
is one other pattern in the interplay of the two AFS Committees: up-down-up. The Turgeon/AFS committee followed
Goodrich/Burch in recognizing several species that research since 1998 has
shown do not warrant recognition at the species level. The 2011 population genetic study of Dillon & Robinson [10], for example, suggested that the “timida” phenotype is
independently derived in populations of Pleurocera floridensis, and in that
same year Dillon (solo) demonstrated an identical phenomenon for the “unciale”
phenotype of P. clavaeformis [13]. These
taxa were recognized at the specific level prior to 1998, lowered to the
subspecies level between 1998-2013, then raised to the species level again by the
Johnson/AFS committee.
The
bottom line is that at least 12-15 pleurocerid nomina listed at the specific level
by the Johnson/AFS committee are (at best) subspecies. But why does this matter? Isn’t everything I
have written in my essays over the last couple months just one big prima donna
sniping at a little clique of other prima donnas over angels on the head of a
pin? Well actually, it matters a
lot. And I will tell you why.
Subspecies are not valid units of
management! I cannot claim any more than a layman’s
understanding of the politics that motivated federal endangered species
legislation in 1973, or the state-level laws and policies that have followed it
in the last 40 years. But it seems to me
that advocates of such policies have, at least in recent years, primarily
rationalized their efforts as desirable for the protection of “biodiversity.”
And (again, I think!) the implication is that such “biodiversity” is supposed
to be heritable. Which means if (as
research suggests) the traits that distinguish pleurocerid populations bearing
nomina valid only at the subspecific level, such as dislocata, viennaensis,
timida and unciale are ecophenotypic responses to the environment, with no demonstrably
heritable basis, efforts directed toward their conservation are unwarranted.
So
at last we arrive at our summary paragraph.
As I mentioned in my February essay, the FWGNA currently recognizes four
sets of subspecies, all in the family Pleuroceridae. We have preserved these subspecific
distinctions primarily for their indexing function – all the nomina involved are
associated with significant (often historic) literature. But we have combined subspecific nomina for
analysis of relative abundance, and for the assignment of FWGNA Incidence ranks
[14]. We make no assumptions regarding
the evolutionary significance of the morphological distinctions upon which
subspecific nomina are based, nor are any (at present) warranted.
Notes
[1]
What is a Subspecies? [4Feb14]
[2]
The situation is complicated. Ravenel
listed Terebra dislocata Say (a marine gastropod) on page 11 of his (1834)
“Catalogue of Recent and Fossil Shells,” with no figure or description. Reeve provided a formal description of Melania
dislocata in his (1861) “Monograph of the Genus Melania,” stating as he did
“The shell here figured is Ravenel’s original type of this species, from the
collection of Mr. Anthony.” So all the
older references, including Tryon and Goodrich, attribute dislocata to Ravenel
(1834). But Burch, Turgeon/AFS and
Johnson/AFS prefer Reeve (1861).
[3]
Goodrich’s appreciation for phenotypic plasticity in the Pleuroceridae has been
a long-running theme on this blog. I’ve
published a series of essays touching on it, notably:
[4]
Goodrich, C. (1942) The Pleuroceridae of the Atlantic Coastal Plain. Occas. Pprs. Mus. Zool. Univ. Mich. 456: 1-6.
[5]
Turgeon, D.D., J.F. Quinn, A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons,
P.M. Mikkelson, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema,
F.G. Thompson, M. Vecchione, and G.D. Williams (1998) Common and scientific
names of aquatic invertebrates from the United States and Canada: Mollusks
(second edition), American Fisheries Society Special Publication 26, Bethesda,
Maryland, 526 pp.
[6]
That’s absurd, of course. The spectacle
of 15 Ph.D. Malacologists convening around a long table to determine which
crappy little brown creek-snails “lay people” can or cannot distinguish, and
inventing “common names” for the former, sounds like a scene from Alice in
Wonderland.
[7]
Chambers (1990) synonymized inclinans and vanhyngiana under Pleurocera
(“Elimia”) floridensis, viennaensis under Pleurocera (“Elimia”) curvicostata,
and albanyensis under Pleurocera (“Elimia”) boykiniana. The sequence data of Mihalcik & Thompson
(2002) and the population genetic survey of Dillon & Robinson (2011) both generally
confirmed the hypotheses of Chambers, although demonstrating that boykiniana is
a junior synonym of Pleurocera catenaria, and suggesting that viennaensis might
go under catenaria as well. In any case,
there is no evidence that any of those five pleurocerid taxa is specifically
distinct: albanyensis, inclinans, vanhyningiana, viennaensis, or dislocata. And there are at least three recent papers
with good, hard data pointing in the opposite direction. See Dillon & Robinson from footnote [10]
below.
[8] On page 13, the “expert in the field of
molluscan systematics who updated the checklist for this volume” for freshwater
gastropods is given as Fred G. Thompson.
[9]
Dillon, R.T. & A.J. Reed (2002) A
survey of genetic variation at allozyme loci among Goniobasis populations
inhabiting Atlantic drainages of the Carolinas.
Malacologia 44: 23-31. [pdf]
[10]
Dillon, R.T., Jr & J.D. Robinson (2011) The opposite of speciation: Genetic
relationships among the populations of Pleurocera in central Georgia. Amer. Malac. Bull. 29: 159-168. [pdf]
[11]
Johnson, P. D., A. E. Bogan, K. M. Brown, N. M. Burkhead, J. R. Cordeiro, J. T.
Garner, P. D. Hartfield, D. A. W. Lepitzki, G. L. Mackie, E. Pip, T. A.
Tarpley, J. S. Tiemann, N. V. Whelan & E. E. Strong (2013) Conservation status of freshwater gastropods
of Canada and the United States.
Fisheries 38: 247 – 282.
[12]
Plagiarism, Paul Johnson, and the American Fisheries Society [9Sept13]
[13]
Dillon, R. T., Jr. (2011) Robust shell
phenotype is a local response to stream size in the genus Pleurocera. Malacologia 53: 265-277. [pdf]
I am quite sure that the Johnson/AFS committee saw this paper, since it
appeared in their cited references.
[14]
What is Rarity? [9Dec13]
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