Pleurocera canaliculata and the Process of Scientific Discovery

Editor's Note - This essay was subsequently published as: Dillon, R.T., Jr. (2019c) Pleurocera canaliculata and the process of scientific discovery.  Pp 71 - 76 in The Freshwater Gastropods of North America Volume 3, Essays on the Prosobranchs.  FWGNA Press, Charleston.

Looking back on my post of two weeks ago [1], I fear I may have left the impression that Rob Dillon is smarter than Calvin Goodrich, and indeed smarter than any other malacologist who has ever waded knee-deep into the rivers of the greater Midwest before or since.  That's probably not an uncommon failing of mine, but nothing could be farther from the truth.  In fact, the revelation that the gastropod populations we have been calling Pleurocera acuta for 189 years are actually the same as what we've been calling Pleurocera canaliculata for 192 only dawned on me after several years of being dope-slapped by the glaringly obvious.  And even then, I was only able to figure out the "Goodrichian" relationship between P. acuta and P. canaliculata backwards, through P. pyrenellum.

So to set the situation aright, I hereby offer an amendment to my essay of 3June13.  And in this retelling I propose to lay bare for my readership the agonizingly slow process by which this particular snail-guy's mind actually works.

The initial revelation that Goodrichian taxon shift might be even more dramatic than Calvin Goodrich himself realized first dope-slapped me in the back of my head eight years ago, as I scored a set of allozyme gels comparing pleurocerid populations from the upper Powell drainage on the Virginia/Tennessee border.  I wrote this the bottom of my data sheet late in the afternoon of October 4, 2005: "Good grief!  Pleurocera unciale and Goniobasis clavaeformis at the mouth of Indian Creek are a single random-breeding population!"  John Robinson [2] and I wrote this initial evidence of Goodrichian taxon shift into a gray literature report in 2007 [3].  I then sampled additional populations of nominal clavaeformis, unciale, acutocarinata, curta, carinifera and vestita across East Tennessee and North Georgia in 2008-09, ran a big mess of additional gels, and published the formal paper subsuming the genera Goniobasis and Elimia under Pleurocera in 2011 [4].

Meanwhile, my general survey of the freshwater gastropod fauna of East Tennessee was moving forward.  I spent at least a week or two working in the rivers and streams between Knoxville and Chattanooga each field season between 2007 and 2010, collecting (what I recorded as) P. clavaeformis (in its various phenotypic forms) in essentially every stream I visited for four years.  And incidentally, I also observed that the big river populations (historically referred to P. unciale or curta) sort-of petered out around Knoxville, to be replaced in the main Tennessee River by Pleurocera canaliculata.

I took a second dope-slap to the back of my noggin at approximately 4:30 PM on August 14, 2010.  Standing knee-deep in Savannah Creek (maybe 20 km N of Chattanooga) on that memorable day, it suddenly struck me that the snails crawling around my feet might be Pleurocera acuta.  At that point in my career, I had collected Pleurocera acuta up in Kentucky, Ohio and Michigan, but would not have expected a P. acuta population anywhere within 500 km of the stream where I was standing.  When I got back to my truck, I wrote this in my field notes: "(star)Wow(star)  Is this Pleurocera acuta??? My eyes are opened!"

So back in Charleston, I pulled four years of old samples off the shelves, dug the old literature out of the file cabinets, and (over the course of several weeks) pieced together the following line of reasoning.

Inference.  The snails I collected in Savannah Creek on 14Aug10 must be what Goodrich would have called "Pleurocera pyrenellum," not Pleurocera acuta.  Goodrich (1940) gave the range of P. pyrenellum as "tributaries of the Tennessee River in Morgan and Lancaster Counties, Alabama, and Walker County, Georgia" [5].  Walker County wasn’t much more than 20-30 km downstream from Savannah Creek.  So "pyrenellum" my snails would seem to be.

Therefore Pleurocera pyrenellum populations inhabit Tennessee tributaries further upstream than Goodrich realized.  Going back through my old collections, I recognized P. pyrenellum at 10-12 additional sites, extending up the Tennessee Valley all the way to the environs of Knoxville [6].  They were usually mixed with populations of P. clavaeformis, and (dazzled as I had been by the phenotypic variety of clavaeformis) I had simply missed them.

Revelation.  Travelling down the main Tennessee valley from Knoxville to Chattanooga, Pleurocera canaliculata begins to appear in the main river (red above) as P. pyrenellum begins to appear in the tributaries (pink).  This was the third major dope-slap I took during my long bewilderment with the East Tennessee Pleuroceridae, although I didn't record the date and time of the whacking.  The relationship between pyrenellum and canaliculata looks exactly like the Goodrichian relationship between unciale/curta and clavaeformis (blue above).

Hypothesis.  But the range of P. canaliculata extends throughout the greater Midwest, up the Ohio River all the way to Pittsburgh, while nominal pyrenellum populations are restricted to drainages of the Tennessee.  So might the small-stream form upstream from all those populations of canaliculata in Ohio, Kentucky, Indiana and Illinois be what everybody calls P. acuta in Yankeeland?

The point of this confession is that my colleagues and I were no more able to see the Goodrichian relationship between acuta and canaliculata standing on the shores of the Wabash River than Calvin Goodrich [7].  I flipped the whole story around when I told it two weeks ago, so that it "made sense," following the conventional practices of science.  I made the process of discovery look logical, even inevitable, when it most certainly was not.  I'm really a bonehead.  Ask my wife.

Allow me to close with another of my philosophical peregrinations.  My regular day-job is teaching majors-level genetics at a very ordinary liberal arts college of regional reputation.  It’s a big chore – there are three or four other members of my department doing the same thing.  All younger than I, of course.

So I organize the subject matter of genetics historically, the way I myself learned it, starting with Mendel, then Morgan, then Beadle then Avery and McLeod and McCarty and Watson and Crick and so forth.  And just when it begins to look like we might get anywhere near the present day, I go back to Hardy and Weinberg and finish with the "Modern Synthesis" of the 1930s and 40s.

Some of my colleagues tell me that undergraduate students "don’t get this."  They prefer to start their majors-level genetics sections with our modern understanding of the molecular basis of inheritance, because given the underlying mechanism, Mendel's 1866 results become a lot easier to explain.  And the kids prefer to focus on today's science, in any case.  They don't care about peas.

That line of argument is so self-evidently horrific to me that in my first draft of this essay, I left it dangling in the wind, without comment.  Like Stede Bonnet on the Charleston battery.

But I shall close with the simple observation that the K-12 teaching of science and the profession of science in higher education are two entirely different things.  In the former we are building palaces, and in the latter we are laying roads.  I trust that my readership has enjoyed this month’s brief foray into road building.  Next month, it’s back to the masonry.

Notes

[1] Pleurocera acuta is Pleurocera canaliculata [3June13]

[2] John D. Robinson was working on his MS in Marine Biology with me at the time.  He went on to earn his PhD at the University of Georgia and has recently moved to the Cornell area.

[3] Goodrichian Taxon Shift [20Feb07]

[4] Dillon, R. T., Jr. (2011)  Robust shell phenotype is a local response to stream size in the genus Pleurocera.  Malacologia 53: 265-277.  [pdf]

• Goodbye Goniobasis, Farewell Elimia [23Mar11]

[5] Goodrich, C. (1940)  The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich. 417: 1 -21.

[6] By the 8/2011 debut of the FWGTN website, I had documented 8 populations of P. canaliculata in the big rivers below Knoxville and 24 populations of nominal "P. pyrenellum" in the tributaries.  Since I've decided to save the nomen "pyrenellum" as a subspecies (more about that in a future post) the distribution of both shell forms is still apparent on the pdf  map available from the P. canaliculata page on the FWGNA site.

[7] In fact, the Indiana survey of Pyron et al. (2008) retained both P. canaliculata and P. acuta as quite distinct species.  For a pdf of Pyron’s survey, see:

• The Freshwater Gastropods of Indiana [23Jan09]

Pleurocera acuta is Pleurocera canaliculata

Editor's Note - This essay was subsequently published as: Dillon, R.T., Jr. (2019c) Pleurocera acuta is Pleurocera canaliculata.  Pp 65 - 70 in The Freshwater Gastropods of North America Volume 3, Essays on the Prosobranchs.  FWGNA Press, Charleston.

I am pleased to report that the second paper in what I expect will be a continuing series on Goodrichian taxon shift in the North American Pleuroceridae has recently reached formal publication [1].  In this most recent installment, the team of Dillon, Jacquemin and Pyron uses a combination of genetic and shell morphometric techniques to demonstrate that the specific nomina acuta (Rafinesque 1824) and pyrenellum (Conrad 1839) are junior synonyms of Pleurocera canaliculata (Say 1821).  As “Pleurocerus acutus” was designated the type of the genus in ICZN Opinion #1195 of 1981 [2], this finding will be of more than the usual taxonomic interest.

Our analytical approach was patterned after that used by Dillon (2011) on the Pleurocera clavaeformis populations of East Tennessee [3].  We used allele frequencies at nine polymorphic allozyme loci to show that two populations of nominal P. acuta (from Indiana and Kentucky) and one population of nominal P. pyrenellum (from north Alabama) were each more genetically similar to the P. canaliculata population immediately downstream than any of the six populations was to any nominal conspecific.  We then used landmark-based morphometics to explore one of these “Goodrichian” shifts in greater detail, the historically important acuta-to-canaliculata transition found in the Wabash River of Indiana.

On at least two occasions Calvin Goodrich himself expressed doubts about the distinction between P. acuta and P. canaliculata, specifically mentioning the Wabash populations in 1937 [4].  So we borrowed 18 lots of historically-collected Wabash Pleurocera from the University of Michigan Museum of Zoology [5] and documented a significant correlation between shell robustness (as measured using relative warp analysis) and river size at point of collection, as estimated by catchment area.  The seven museum lots bearing more slender, high-spired shells (collected above Wabash River kilometer RK500) were identified by Goodrich as acuta, and the six lots bearing broader, heavier shells collected downstream from RK400 were identified as canaliculata.  Goodrich recognized a mixture of the two nominal species in the five lots collected in the 100 km immediately downstream from RK518, where the Tippecanoe River joins the Wabash, essentially doubling the catchment area (sites 8 - 12 in the map below).

Situations such as we document in the RK400-500 region probably explain why Calvin Goodrich, the man for whom Goodrichian taxon shift was named, did not synonymize acuta under canaliculata himself back in 1939.  The two nominal “species” sometimes seem to mix and retain a degree of distinctiveness.  The phenomenon appears even more dramatically in places where very small streams communicate directly with large mainstem rivers, such as that marked “12” in the map below.  It is not unusual to find snails bearing very slender, high-spired shells washed down into much broader, more robustly-shelled populations inhabiting the main river at spots such as this, looking for all the world like a pair of bona fide, reproductively-isolated species.

Way back in 2007 I defined "Goodrichian Taxon Shift," as “intraspecific variation in freshwater gastropod shell morphology along an environmental cline of such magnitude as to prompt the erroneous recognition of multiple nominal taxa” [6].  The phenomenon was conceived as narrowly applicable to freshwater snails, as Calvin Goodrich himself focused his own research.

But after some soul-searching, my colleagues and I have decided to broaden the concept and coin a new term for it.  So in our paper just published, we propose the term “cryptic phenotypic plasticity,” which we define as “intrapopulation morphological variation so extreme as to prompt an (erroneous) hypothesis of speciation.”  We think that the sort of insight Calvin Goodrich brought to the study of pleurocerid snails in the 1930s and 1940s has the potential to make a contribution to the understanding of evolutionary processes beyond our small community of freshwater gastropod cognoscenti, even in the present day.

Goodrich himself was strongly influenced by the research of A. E. Ortmann on unionid mussels.  Ortmann described a correlation between river size and shell robustness way back in 1920, on the basis of which he sank quite a few unionid taxa into synonymy [7].  And Ortmann credited the idea to Wilson & Clark (1914) [8].  So in some sense it might not be fair to continue to call the phenomenon “Goodrichian” anything, as we forward cryptic phenotypic plasticity onward to evolutionary science as a whole.

The extent to which cryptic phenotypic plasticity may occur in the biotas of land and sea remains to be seen, however.  It seems unlikely to me that marine and terrestrial environments manifest themselves as variably to the populations that inhabit them as fresh waters, at least for the molluscan fauna with which I have any professional familiarity.  Were the Nucella (“dog whelk”) populations of the Pacific intertidal an (historic) example of cryptic phenotypic plasticity?  What component of the baroque taxonomy of Cerion populations in the Bahamas might be attributable to ecophenotypic plasticity in their shells [9]?  Our colleagues with expertise in environments such as these are hereby invited to take notice.

Notes

[1] Dillon, R. T., Jr., S. J. Jacquemin & M. Pyron (2013)  Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117-127.  [html] [pdf]

[2] Joe Morrison and the Great Pleurocera Controversy [10Nov10]

[3] Dillon, R. T., Jr. (2011)  Robust shell phenotype is a local response to stream size in the genus Pleurocera.  Malacologia 53: 265-277.  [pdf]

• Mobile Basin III: Pleurocera Puzzles [12Oct09]
• Goodbye Goniobasis, Farewell Elimia [23Mar11]

[4] Goodrich, C. (1937)  Studies of the gastropod family Pleuroceridae – VI.  Occas. Pprs. Mus. Zool. Univ. Mich. 347: 1 – 12.

Goodrich, C. (1939)  Pleuroceridae of the St. Lawrence River basin.  Occas. Pprs. Mus. Zool. Univ. Mich. 404: 1 – 4.

[5] The UMMZ was Goodrich’s home institution from 1924 to 1944.  All the pleurocerid lots curated during this period would have been identified by him, if not collected by him personally.  See “The Legacy of Calvin Goodrich.” [23June07]

[6]  Goodrichian Taxon Shift [20Feb07]

[7] Ortmann actually did this backwards.  In his (1918) “The Nayades of the Upper Tennessee Drainage, with Notes on Synonymy and Distribution” (Proc Am Phil Soc 57: 522) he wrote, “A large number of the ‘species’ described by Lea… and of those listed by Lewis… and subsequently described by various authors…are mostly synonyms.”  And as evidence he cited, “a rule…that one and the same shell assumes different shapes in the large rivers and in small streams and headwaters, a rule the existence of which will be shown elsewhere.”  Then in 1920 Ortmann published his “Correlation of shape and station in freshwater mussels (naiades)” (Proc Am Phil Soc 59: 269-312).

[8]  Wilson, C. B. & H. W. Clark (1914)  The mussels of the Cumberland River and its tributaries.  Bur. of Fisheries 781: 1 – 63.

[9]  I thought Woodruff & Gould pretty much answered this question back in the 1980s (eg, Biol. J. Linn. Soc 14: 389-416).  But Harasewych (Nautilus 126: 119-126) seems not to have been paying attention.

The Mystery of the SRALP: "No Physa acuta were found."

Editor's Notes - If you’re just joining us.  This is the fourth and final installment in my 2013 series on the Snake River Physa controversy.  It won’t make any sense unless you back up and read February, March and April first.  I’m serious, I mean it, and I’m in no mood to be trifled with, this month in particular.

This essay was subsequently published as: Dillon, R.T., Jr. (2019d) The Mystery of the SRALP: No Physa acuta were found.  Pp 187 - 192 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

Over two years have passed since the Dixie-cup showdown in Boise, and I will admit that I have been anticipating the formal publication of the Gates & Kerans report with mixed emotions.  On the one hand, I was pleased to see that the replacement of the Minidoka Dam spillway was approved shortly after our meeting in September of 2010 [1] and that actual construction got underway in November of 2011.  On the other hand, the “Record of Decision” published by the USBR after our September meeting contained language strongly implying that its water management options had been significantly narrowed by the presence of putatively endangered physids in the Minidoka tailwaters.  And a regular program to monitor physid populations has been continued through the duration of the spillway replacement project, to the present day.

So the Gates & Kerans paper was published online in late December, with old-fashioned paper publication following in February of 2013 [2].  And I was initially encouraged to see that a substantial volume of fresh sequence data has been added since 2010, and that the authorship has been expanded to include John Keebaugh, Steven Kalinowski, and Ninh Vu [3]. But my heart sank when I read these five words: “No Physa acuta were found.”

As I flipped through the pages of the PDF reprint I recognized much that was familiar: the heroic 2006-08 survey of the Minidoka Dam tailwaters yielding 274 small, oddly-shaped physids, the anatomical observations “courtesy of John B. Burch,” and the mtDNA gene trees with outgroups fished from GenBank, none sampled closer than Wyoming.

In addition, the authors reported an expansion of their mtDNA survey to include a very peculiar sample of physids collected hundreds of miles downstream from the Minidoka Dam (RM 675), all the way across southern Idaho.  Here is the single line from their methods section relevant to this enlarged sampling effort, quoted verbatim: “Museum dredge samples collected from the Snake River between RK 322 (RM 200) and RK 948 (RM 589) from 1995 to 2003 were re-examined to determine species distribution.”  The authors did not offer any explanation regarding the gear or methodology used for “dredging,” but one might infer that samples thus obtained came from deeper water, not from the shallows.

The (N=19,427!) individual physids in this “museum dredge sample” were screened for their match to Taylor’s [4] original description of the P. natricina shell: “small size (maximum of 4.8 – 6.9 mm shell length, plotted above), ovoid shape, inflated body whorl, well-impressed suture, broadly rounded anterior end with a wide aperture making the greatest width anterior to the midlength of the shell, microsculpture of oblique growth lines, and a series of parallel spiral lines consisting of curved arcs with their concavity toward the shell aperture.”  Through this elaborate winnowing process passed 52 individuals (collected from RM 559 to RM 368), 15 of which yielded mtDNA sequence data.  All 15 of the new, downstream mtDNA sequences matched the sequences previously recorded from the Minidoka tailwaters and referred to Physa natricina in 2010.

Gates and colleagues concluded, “Our results confirm the original description of P. natricina as an endangered species and expand the extant distribution” some 200 river miles downstream from the range suggested by Taylor, all the way across Idaho into Hells Canyon on the Oregon border.

And you found no Physa acuta?  Did you even consider getting off I-84 anywhere between Twin Falls and Boise, driving five miles south, wading ankle-deep, bending over and simply picking up any of the plain, ordinary, crappy, acuta-like Physa that you have been repeatedly told for five years [5] are as common as cockroaches in that river?  Or did you gin up a meticulous sampling scheme cynically designed to exclude the 99.7% of the snails in your sample that might possibly be identified as a Physa acuta?

No Physa acuta were found?  Did you even look on Sunday morning, 19Sept10, when we visited the Minidoka tailwaters together [6]?  Or did three of you literally turn your backs on me and spend hours sampling a habitat where you knew no Physa acuta (of any standard morphology) could possibly be found, in an overt and calculated effort not to find them?

No Physa acuta were found?  What did you do with the 30 snails I handed you [7] on Monday morning, 20Sept10, before God, the Bureau of Reclamation, the US Fish & Wildlife Service, and the choir of malacologists invisible?  Flush them down the toilet?

No Physa acuta were found?  Carve it on the tombstone of the misbegotten excuse for a science that calls itself “Conservation Biology.” 

Science and politics do not mix.  When they have bastard children, science is recessive.  Gates, Kerans and their colleagues may have positioned themselves well to write new proposals, win new grants, train more students and perpetuate their wretched enterprise in the waters of the Snake River for years to come.  But I am done with it.

Notes

[1] A nice selection of documents having to do with the Minidoka Dam Spillway Replacement project, including the Environmental Impact Statement and the Record of Decision, are available from the USBR website here: [USBR Minidoka page]

[2] Gates, K. K., B. L. Kerans, J. L. Keebaugh, S. K. Kalinowski & N. Vu (2013) Taxonomic identity of the endangered Snake River physa, Physa natricina (Pulmonata: Physidae) combining traditional and molecular techniques.  Conserv. Genet. 14: 159-169.  [html]

[3] I was surprised not to find the name of John B. Burch among the authors.  On 21July09 I was in the audience for a seminar given by Prof. Burch at the AMS meeting in Ithaca, where he presented a great deal of background information on P. natricina as the senior author of a paper with John Keebaugh and Taehwan Lee.  And at the Boise meeting of 20Sept10 he defended the morphological observations as though they were his own.

[4] Taylor, D. W. (1988) New species of Physa (Gastropoda: Hygrophila) from the western United States. Malac. Rev. 21: 43-79.

[5] Rogers, D. C. & A. R. Wethington (2007) Physa natricina Taylor 1988, junior synonym of Physa acuta Draparnaud, 1805 (Pulmonata: Physidae). Zootaxa 1662: 45-51.

[6] The Mystery of the SRALP: A twofold quest!  [1Mar13]

[7] The Mystery of the SRALP: Dixie-cup showdown!  [2Apr13]

SFS Meeting Jacksonville, May 19 - 23

To the FWGNA Group:

This is a cordial invitation to any of our friends who might be packing for next month's meeting of the society formerly known as NABS.  Please stop by to see me at the "Taxonomy Fair" Wednesday afternoon!  And feel free to bring any problematic samples of freshwater gastropods you may have accumulated in your cabinet drawers.

Looking forward to it,
Rob

The Mystery of the SRALP: Dixie-Cup Showdown!

Editor's Notes - If you’re just joining us.  This is the third installment in my 2013 series on the Snake River Physa controversy.  It won’t make any sense unless you back up and read my February and March posts first.  I’m serious, I mean it.

This essay was subsequently published as: Dillon, R.T., Jr. (2019d) The Mystery of the SRALP: Dixie Cup Showdown!  Pp 181 - 185 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

So the highly-improbable team of Newman, Keebaugh, Burch and Dillon reunited at the Bureau of Reclamation’s Boise field office on Monday morning, September 20, 2010, for the purpose of reviewing the Gates & Kerans Report.  In addition to the four of us fresh from our adventures in the tailwaters of the Minidoka Dam, and authors Gates & Kerans themselves, also present for the meeting were four additional Bureau of Reclamation personnel and five representatives of the US Fish & Wildlife Service, for a total of 15 participants. 

And Ms. Gates, for her part, did a fine job with the presentation.  My general impression of her (and of her advisor, Dr. Billie Kerans) was that they are two earnest and hardworking researchers trying to do their jobs as best they can with the tools God gave them, bless their hearts.

Their survey of the Minidoka tailwaters, which was (after all) the job they were paid to do, was marvelously well-executed.  But with the publication of the Rogers and Wethington paper in late 2007 [1], their study was “overtaken by events” [2].  At that point the only appropriate control for any datum they might have collected became the population Physa indistinguishable from P. acuta inhabiting the Snake River shallows (the “SRALP”), and none of their observations can have any meaning without that appropriate control.

So throughout Ms. Gates’ presentation, the 25-30 acuta-like Physa that I had collected at Snake River Mile 600 the previous afternoon were blissfully crawling about in the drinking cup on the conference table in front of us.  And when my turn came to comment on her report, I transferred my cup of SRALP-snails to Prof. Keebaugh, who had been serving as curator for the project.  Here, I announced to the 15 biologists and managers assembled, is the appropriate control for the research we have just heard presented.

Might the sample of 274 little physids heroically recovered from the Minidoka tailwaters by Gates & Kerans match my sample of SRALP from RM 600, genetically and morphologically?  I stressed that this question is not merely academic; that it has management implications.  If no, then more water should be released from Minidoka Dam to better match the habitat of an endangered “Physa natricina” narrowly adapted to deep rapids, and less should go to the potato fields fed by the irrigation canals leading north and south.  But if yes, and if indeed one wanted more trash snails like those crawling about on the conference table in front of us, as much water as possible should be sent to the potatoes, and as little as possible through the gates of the dam.  Then the tailwaters of the dam would pond up, warm, and more closely approximate the acuta-friendly habitats downstream.  I concluded that since the Gates & Kerans report did not address this question, no recommendations were possible at that time.

Rising to the defense of the Gates & Kerans report was Prof. John B. Burch.  It was Prof. Burch’s opinion that Physa acuta do not inhabit the Snake River, nor indeed is P. acuta even native to North America.  He asserted that Physa acuta is a European species, rarely introduced to the New World, if at all.  With regard to the breeding data from my lab suggesting otherwise [3], he was dismissive, failing to see the relevance of experiments “done in Dixie cups.”  Our culture vessels are 12-ounce drinking cups of clear plastic, I corrected him.  That our experiments have been conducted in Charleston is the only Dixie thing about them.

What, I asked Prof. Burch, is the anatomical difference between the 274 little physids recovered by Gates & Kerans and invasive pest populations of Physa acuta from any of six continents he’d like to name, other than size?  I challenged him to put his finger on the anatomical drawings to show me one, single distinction.  Gates & Kerans screened their sample by restricting shell heights to no greater than 6.9 mm, the maximum specified by Taylor [4].  Did Prof. Burch have any comparable observations on 6.9 mm Physa acuta?

The exchange between Prof. Burch and myself was rather heated at times.  In retrospect it must have been quite a show for the roomful of natural resource managers assembled to see such passion exercised over such arcane subject matter.

We, the outside experts were excused at 10:00 AM, leaving the managers to reconvene after a break for decision-making.  Burch, Keebaugh, Newman and Dillon shook hands in the parking lot, although the pleasantries may have been a bit strained.  John Keebaugh departed with the container of acuta-like Physa I had collected at RM 600, which I felt certain he would convey to Gates & Kerans and whoever their collaborators might be for sequencing.  And setting aside all the controversy of the morning, the mystery of the SRALP should at last be solved.

Or will it?  Join us again next time for the final installment in the Mystery of the SRALP… “No Physa acuta were found.”

Notes

[1] Rogers, D. C. & A. R. Wethington (2007) Physa natricina Taylor 1988, junior synonym of Physa acuta Draparnaud, 1805 (Pulmonata: Physidae). Zootaxa 1662: 45-51

[2] This is a term I learned during my AAAS fellowship year on Capitol Hill.  It means “obsolete” without the harsh connotation.

[3] Dillon, R. T., A. R. Wethington, J. M. Rhett and T. P. Smith.  (2002)  Populations of the European freshwater pulmonate Physa acuta are not reproductively isolated from American Physa heterostropha or Physa integra.  Invertebrate Biology 121: 226-234. [PDF]

Dillon, R. T., A. R. Wethington and C. Lydeard (2011) The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa.  BMC Evolutionary Biology 11: 114. [PDF]

See also my post of [12July11] "What is a Species Tree?"

[4] Taylor, D. W. (1988) New species of Physa (Gastropoda: Hygrophila) from the western United States. Malac. Rev. 21: 43-79.

The Mystery of the SRALP: A Twofold Quest!

Editor’s Notes – If you're just joining us.  This is the second installment in my 2013 series on the Snake River Physa controversy.  It won’t make any sense unless you back up and read my February installment first.  It might also help to read my essays of March 2008 and September 2010, but the most important thing is to read last month’s post, before trying to read this one.  I’m serious, I mean it.

This essay was subsequently published as: Dillon, R.T., Jr. (2019d) The Mystery of the SRALP: A Twofold Quest.  Pp 173 - 180 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

The rendezvous was set for 9:00 Sunday morning, September 19, 2010, at a gas station by the interstate near Burley, Idaho.  We were four biologists of strikingly different agendas, drawn together on a twofold quest.  And I suppose I should not have been surprised, but I was.

When I first suggested a field trip to the Minidoka Dam to Mr. Ryan Newman, my Bureau of Reclamation host, I had imagined that I would go alone.  I thought perhaps he’d call the staff on duty for me, maybe get somebody to open a gate on a Sunday morning, and I’d be fine.  I was pleased (of course) to discover that he was willing to accompany me as my native guide, and pleased again to see our good friend John Keebaugh’s email address on the CC line.  John works out of the Orma J Smith Museum at the College of Idaho in Caldwell, about 150-200 miles west, back near Boise.  But the fourth member of our party, chauffeured in by Mr. Newman as John Keebaugh and I stood chatting in the parking lot that morning, was a surprise.  Dr. John B. Burch, all the way from Ann Arbor.

Dillon, Burch & Keebaugh

My agenda on the Snake River that morning was simple – to test the hypothesis I first advanced in my essay of March 2008 [1].  Based on the observations of Rogers & Wethington [2], it seemed likely to me that Physa acuta, or some snail not immediately distinguishable from Physa acuta (which we are calling the Snake River acuta-like Physa, or “SRALP”) should inhabit the shallow backwaters downstream from Minidoka Dam.  This would be consistent with the greater hypothesis, that outliers on the margins of acuta-like populations may have colonized more rapid midstream environments of the Snake River, inducing the phenotype we identify as Physa natricina.

It materialized that my three colleagues, on the other hand, were bent on sampling the deeper waters for additional specimens bearing the natricina phenotype.  The rationale for this behavior escaped me, as the existence of small-bodied physid populations bearing wide apertures in the deeper Minidoka tailwaters had already been well-established by the heroic survey of Gates & Kerans, which prompted this field trip in the first place. One would think, if the little things were indeed elements of an endangered species, we would leave them alone.  But no.

John Keebaugh had brought a long-handled dipper with which, wading into the river waist deep and extending to full length, he was able to retrieve cobbles from some rather great depth.  Ryan Newman and Jack Burch sorted through trays of these dredgings, looking for physids.

Meanwhile, I enjoyed a fresh, sunny morning wading around in the Snake River shallows all by myself, looking for the sorts of ponds and protected backwater areas that one might think of as typical Physa acuta habitat.  And finding slick-rock nothing.

It turns out that the Snake River below Minidoka Dam is a really crappy habitat, for snails or indeed for macroinvertebrate benthos of any sort.  Our team visited three sites, from River Mile 675 just below the spillway to River Mile 670 at the Jackson Bridge.  And throughout that five mile stretch, it was my impression that river levels are terribly impacted by the generation schedule at the dam.  On the September day of our visit we found a couple vertical feet of cobble beach exposed, and I would estimate that the water levels regularly fall another 3-4 vertical feet below that.  So even wading knee deep and squinting as far as I could into the dark, roiling river, I probably couldn’t see to any bottom that hadn’t been dewatered last May, and wouldn’t be dewatered again come December.

I did find a few Physa gyrina in the shallows – mostly on sticks and organic debris – probably washed in from little side tributaries [3].  In fact, the only really nice snail population I saw all morning was the Physa gyrina in a seep near the base of the spillway [4].  But I found no acuta-like Physa in the Minidoka tailwaters [5].  That turned out to be a really, really crappy habitat.

So we ate lunch and I bid my colleagues adieu.  And I hopped back into my rental car and turned my attention toward a (rather poor) roadmap I found in the glove compartment.  And began planning a blitzkrieg survey of the Snake River further downstream, on my return trip west, back toward Boise.

Snake R from the US93 Bridge

At this point a brief orientation might be helpful.  The Snake River runs east to west like a giant smiley-face across the bottom of Idaho, then north along the Oregon border through Hells Canyon to join the Columbia River at Kennewick, Washington, there designated “Snake River Mile 0.”  So Minidoka Dam is in eastern Idaho, at river mile RM 675.

Rogers & Wethington [2] never promised us any Physa acuta as high as RM 675.  They reported that their sample of 211 physids collected between RM 573 and 340 contained 94% of the “Physa acuta group.”  Nor did Dwight Taylor list any localities upstream as high as Minidoka County in his original description of Physa natricina [6].  His natricina localities were in Gooding, Elmore, and Owyhee counties, roughly RM 571 – 525.

It looked to me as though the Milner Dam (located at RM 639) backed the Snake River up almost to the Jackson Bridge, where I sat parked early that Sunday afternoon.  So I rather arbitrarily set my course for the US 93 bridge near Twin Falls, further downstream at RM 611.  The river turned out to be inaccessible from the US 93 bridge, but I was able to follow signs down to a public access at the Magic Valley Hatchery, RM 600.

The Snake River at RM 600 had taken an entirely different character from the flashy, sterile thing I’d waded around in all morning.  It was broad and warm and shallow and rich [7].  And the rocks on the quiet margins were covered with SRALP-snails, indistinguishable to my eye from Physa acuta.  It didn’t take me ten minutes to squat down and collect at least 25 – 30 individuals in a drinking cup, which I resolved to carry with me to the meeting in Boise Monday morning.

Thousand Springs area

Then I got back into my rental car and continued driving east, enjoying the lovely weather and the countryside all quite exotic to my eastern eyes.   I made three additional stops, all brief: at the Owsley Riverfront Park (RM 582), at Bliss (RM 565) and at Glenns Ferry (RM 538), just as the sun was setting.  The river looked rich at all these spots, with a nice, diverse pulmonate fauna.  The population of Potamopyrgus (“New Zealand Mud Snails”) at Owsley was strikingly dimorphic, which was interesting [8].  And I enjoyed the big Fluminicola population at Bliss, the first I’d ever seen on the hoof.  And at all three spots I found SRALP-snails at least moderately common.  I picked up a few at each site and kept going.  I saw no Physa gyrina anywhere in my quick tour of the Snake River between RM 600 and RM 538 at all.

Back in Boise that night I slept soundly, my sample of SRALP crawling peacefully around the drinking cup at my bedside.  Surely, I thought, everybody at the big Bureau of Reclamation meeting on the morrow would see the importance of these snails to the answer of our ultimate question.  Does the strange little physid population in the Minidoka tailwaters that Gates & Kerans refer to “Physa natricina” indeed represent an endangered species?  Or might they be ecophenotypic variants of an otherwise common species, nevertheless endemic to the Snake/Columbia system?  Or might the Gates & Kerans sample simply constitute 274 ecophenotypic variants of the invasive pest Physa acuta, found everywhere on six continents?

How naïve could I be?  Join us again next time, for … Dixie-Cup Showdown!

  

Notes

[1] Red Flags, Water Resources, and Physa natricina [12Mar08]

[2] Rogers, D. C. & A. R. Wethington (2007).  Physa natricina Taylor 1988, junior synonym of Physa acuta Draparnaud, 1805 (Pulmonata: Physidae)  Zootaxa 1662: 45-51.

[3] To be as complete as possible.  I did collect approximately 15 - 20 juvenile and subadult Physa from the Minidoka tailwaters that I thought, on the morning of 19Sept10, might be Physa acuta.  I brought them home with me to Charleston, reared them to adulthood, and then dissected them.  Nope, they were all Physa gyrina.

[4] One of the strongest memories I have from my very brief introduction to the Minidoka tailwaters on a bitterly cold morning in December of 2005 was the high density of Potamopyrgus.  But on my return visit in September of 2010 I found exactly N=0 in several hours of effort.  The river levels were significantly higher in 2010, so it’s possible that I simply missed them.  Or has there been a flush/crash?

[5] So my hypothesis of 3/2008 was incorrect.  Physa gyrina seems to be washing into the shallows below Minidoka Dam, not Physa acuta.  My new hypothesis is that the little population of snails that Gates & Kerans are calling “Physa natricina” is the relict of a much larger acuta-like population comparable to those inhabiting the Snake River further downstream, but now extinguished from the shallows by operations at the dam.

[6] Taylor, D. W. (1988)  New species of Physa (Gastropoda: Hygrophila) from the western United States.  Malacological Review 221: 43-79.

[7] Although similar in outward appearances, P. acuta and P. gyrina have diverged strikingly in their life history adaptation.  Populations of P. acuta are weedy or “ruderal” – their rapid growth, quick maturity and high reproductive output (relative to body mass) adapted to exploit rich, although often unpredictable habitats.  Physa gyrina are more stress-tolerant (like a cactus), adapted to nutrient poor but nevertheless predictable habitats.  See my book (Dillon 2000) pp 131-136 and Fig 8.10 for more.  In southern Idaho, these life history differences seem to be reflected in the distributions of the two species – acuta in the main river (further downstream) and gyrina in the tributaries.

[8] The presence of two strikingly different shell forms in a single Potamopyrgus population would seem to suggest sexual reproduction.  The Snake River gastropod fauna really does offer a wealth of opportunity for important scientific research, if serious scientists could get beyond all the politics and confusion.  Such a shame.

The Mystery of the SRALP: A Bidding...

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019d) The Mystery of the SRALP: A Bidding...  Pp 165 - 171 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

The invitation arrived by email on 19Aug2010.  Mr Ryan Newman of the US Bureau of Reclamation (USBR) was curious to know whether I might be available to join a working group convening in Boise to review a report by K. Gates & B. Kerans entitled, “Snake River Physa, Physa (Haitia) natricina, survey and study.”  And so began one of the greater malacological adventures of my life, professional or otherwise.

Faithful readers may remember my post of March 2008 regarding the federally-endangered Physa natricina [1].  Described by Dwight Taylor (1988) in one move of an (ultimately successful) effort to thwart the impoundment of the last free-flowing section of the Snake River in southern Idaho, the species was for many years a phantom – no precise localities known, even the type specimens lost.  Its habitat seemed to be unique among physids, “on boulders in the deepest accessible portion of the Snake River near rapid margins” [2].  The adults were unusually small-bodied (shell length “5.4 – 6.9” mm), bearing an unusually wide aperture.  See note [3] for more about the photo below.

Taylor went to some length to distinguish his Physa natricina from Physa gyrina – the former having a one-part penial sheath (“type-c”) and the latter a two-part sheath (“type-b”).  But in late 2007 Rogers and Wethington [4] pointed out that Taylor’s anatomical description was not sufficient to distinguish P. natricina from the worldwide invasive P. acuta*, another type-c physid apparently common in the shallows throughout most of the Snake.  Since stunted size and an odd aperture might simply reflect ecophenotypic responses to life in a habitat to which physids are marginally suited at best, Rogers and Wethington synonymized Taylor’s nomen natricina under P. acuta.  One might think this would end the matter.

But a controversy every bit as political as that which prompted the 1992 listing of Physa natricina had been simmering for some years in the Snake River tailwaters below Minidoka Dam, 20 miles upstream (NE) of Burley.  There macrobenthic surveys conducted in the mid-1990s by biologists working for the Bureau of Reclamation had returned small, oddly-shaped physids identified by consultants in 2004 as Physa natricina.  This prompted the US Fish & Wildlife Service to issue a “Biological Opinion” in March of 2005 [5] affecting the USBR’s management [6] of Minidoka Dam.  So in August of 2005 the USBR commissioned a study [7], which by August of 2010 had yielded fruit.  And I was being invited to review the result.

The 87-page Gates & Kerans report attached to Mr. Newman’s bidding comprised three sections – a survey, a morphological study, and a DNA sequence study.  The survey section spun a ripping-good yarn of suction dredges and tethered scuba divers, ultimately triumphing in the recovery of a remarkable 274 small, oddly-shaped type-c physids from the roiling waters of the Snake River below Minidoka Dam.  The second section reported a conventional study of the shell and anatomy of six of these small snails, featuring a photo of a couple living individuals (“courtesy of John B. Burch”).  And the third section, contributed by collaborators at both Montana State and the University of Michigan, reported an average 19.7% mtDNA sequence divergence between approximately 30 of these little snails (combined over both labs) and a sample of Physa gyrina.

And here’s the headline.  Gates &  Kerans reported an eye-popping 17.1% average sequence divergence between their sample of small, oddly-shaped type-c physids and Physa acuta sequences retrieved from Genbank.

But alas.  Gates & Kerans seemed entirely ignorant of (or worse, dismissive of?) the Rogers and Wethington report of Physa acuta* in the Snake River.  And the nearest P. acuta sequence available for comparison in GenBank had been sampled 500 km NE of the Minidoka Dam, on the other side of the Rocky Mountains in Wyoming.  And Gates & Kerans had not (apparently) felt called to sample their own.

Granted, the Rogers and Wethington study was not published until after the 2007 field season, by which time two years of data were already in the can.  But it seemed to me that, as soon as the existence of P. acuta* in the Snake River became known, those populations became the only appropriate control for the study of P. natricina, not P. acuta sampled across the continental divide 500 km northeast, and certainly not P. gyrina. The relevant morphological comparison would be between the population of small, oddly-shaped type-c Physa at mid-river in the Snake and equally small P. acuta* sampled from its shallows.  Gates and Kerans needed DNA samples from Snake River acuta*; neither Snake River gyrina nor Wyoming P. acuta were germane.

At this point in our malacological adventure I find it convenient to introduce a new term, “Snake River acuta-like Physa,” or SRALP for short.  And request that my readership mentally replace all five instances of the binomen "Physa acuta” marked with asterisks above with “SRALP.”  And find it necessary to reverse the flow of my narrative once again, back to an essay I wrote in September, 2010 [8].

That particular essay was prompted by the de-listing of Valvata utahensis and Pyrgulopsis robusta, two of the other four freshwater gastropod species politically listed in 1992 to block the Snake River impoundment.  In that 2010 essay I made reference to what seemed like a logical progression of three hypotheses – narrow endemic, regional endemic, and nonendemic – and lamented how natural resource politics had for 20 years short-circuited the (otherwise orderly) examination of all three.  And toward the end of that essay I pointed out that, in the case of Physa natricina, nobody seems to have given any study to “Hypothesis #2 (of 3)” at all.

The Gates & Kerans report was on my desk at the time I wrote my 2010 essay, and the timing was not a coincidence.  Does the Gates & Kerans sample of 274 small type-c Physa come from a narrowly endemic species, restricted to “boulders in the deepest accessible portion of the Snake River,” best identified as Physa natricina?  Or perhaps those 274 snails are simply ecophenotypic variants of the nonendemic P. acuta, otherwise common in the Snake River backwaters and elsewhere throughout the world?  Or might the Snake River be home to a regional endemic – locally common and practically indistinguishable from acuta in the calm backwaters, but rare, stunted and misshapen in the rapids?  The names concolor (Haldeman 1843) and columbiana (Hemphill 1890) are already in the literature for this second (of the three) possibilities. 

The answer to these questions and more would rest in the SRALP.  What exactly is that population of type-c physids reported common in the Snake River by Rogers and Wethington?  And what might their relationship be to the 274 odd little physids heroically retrieved by Gates & Kerans?  Tune in next time, as we journey to southern Idaho, on a quest!

Notes

[1] Red flags, Water Resources, and Physa natricina [12Mar08]

[2]  The “deepest accessible portion” quote comes from Taylor’s (1982) “Status Report on Snake River Physa Snail” (USFWS, Portland).  Taylor’s formal description of 1988 did not include habitat notes of any sort, oddly.

[3] The shell labelled "natricina" was dead-collected in the "drift" on one of the rocky beaches below the Minidoka Dam on 19Sept10.  Its collector was John Keebaugh, who identified it and made a gift of it to me.  I myself had collected the P. gyrina from a seep near the Minidoka Dam spillway earlier that morning.  And I also collected the individual labelled "SRALP" (Snake River acuta-like Physa) later that same day from the Snake River at Owsley (RM 582).  More in our next installment.

[4] Rogers, D. C. & A. R. Wethington (2007)  Physa natricina Taylor 1988, junior synonym of Physa acuta Draparnaud, 1805 (Pulmonata: Physidae).  Zootaxa 1662: 45 – 51.

[5] USFWS (2005)  Biological Opinion for Bureau of Reclamation Operations and Maintenance in the Snake River Basin Above Brownlee Reservoir.  This and all the other documents regarding the 2004-05 Minidoka controversy (including the implementation plan for a Physa study) are available from the Bureau of Reclamation here: [USBR 2004 Biological Assessment].

[6]  All the 2005 fussing (that came to my ears, anyway) focused on the annual schedule of water release from the Minidoka Dam, the FWS pressing for something closer to natural flow.  It also turns out that the USBR had been studying the complete replacement of the Minidoka Dam spillway since at least 2000, although I didn’t hear about that element of the controversy until 2010.  Here is the USBR page with all the documents relating to the spillway replacement: [USBR Spillway Replacement].

[7] To be as complete and fair as possible.  My first visit to Minidoka Dam came in December of 2005 as a member of a “Snake River Physa Technical Team” convened by the Bureau of Reclamation to provide recommendations for their study (documents at Note 5 above).  At the time, there was real concern that even if any small, misshapen type-c physids might be recovered from the Minidoka tailwaters, nobody could positively confirm their identity as P. natricina.  And I had not heard another word about the project as of 12Mar08, hence the reference to “a day which never arrived” in my 2008 blog post. 

But (in fact) the Gates & Kerens study was already into its third year by the spring of 2008.  I was invited to a second meeting of the Snake River Physa Technical Team on 1May2008, although not offered any funding to get me there.  So I told Mr. Newman that “if I happen to be in Boise on May 1, I’ll drop by.”  I would nevertheless have been happy to read a written progress report, had Mr. Newman offered one in 2008, which he did not.  Thus the desirability of standards and controls in scientific investigation was not called to the attention of Gates & Kerans until the fall of 2010, by which time there seems to have been little opportunity for a remedy.

[8] Valvata utahensis and Hypothesis #2 (of 3)  [14Sept10]