Delaware, and what we think we know, that we do not

Editor’s Note. This essay was subsequently published as: Dillon, R.T., Jr. (2019d) Delaware, And What We Think We Know, That We Do Not.  Pp 235 - 241 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

Delaware, our first state, is surprisingly diverse.  Its Piedmont north is primarily industrial and urban, but there are some lovely (and surprisingly rich) rocky streams tumbling across the low fall line.  Large, prosperous farms dominate the sandy coastal plain of the south, where I was personally startled to find blackwater swamps, dominated by bald cypress.  And with the Delaware Museum of Natural History in Wilmington, the Academy of Natural Sciences 20 miles north in Philadelphia and the National Museum of Natural History 70 miles east in Washington, the state of Delaware is cradled in the greatest concentration of malacological talent in the USA, if not the world.

Should we be surprised to learn that Delaware has never seen a survey of its freshwater gastropod fauna?  Or that the systematic collections of the DMNH, the ANSP and the USNM hold but 151 lots of freshwater gastropods collected in The First State combined, under 31 nomina, 11 of which are misidentifications or junior synonyms?  It seems likely to me that this situation arises from some sort of “neglected backyard effect,” our North American imaginations so transfixed by the Brazilian Amazon and the Black Smokers of the Abyss that we tend to overlook the little creeks running through our own city parks back home.

I am now pleased to report that a remedy is at hand.  In coming months the FWGNA project will roll out a new website entitled, “The Freshwater Gastropods of the Mid-Atlantic States” which will include surveys of Delaware, Maryland, New Jersey, eastern Pennsylvania, and the West Virginia panhandle.  Our extensive original collections, sampled from approximately 144 sites spread down the 100 mile length and across the 30 mile breadth of The First State, will confirm that a fairly reliable estimate for the number of gastropod species inhabiting the freshwaters of Delaware is indeed 20, as might have been predicted from the meager museum records available.

We will be sharing much more detail about the freshwater gastropods of all the Mid-Atlantic states in the coming months.  My focus for the remainder of this essay is not on what we now know, but on what we thought we knew, that we did not.

I am not a fan of the nonprofit environmental group called, “NatureServe,” or its online database “Explorer.”  But if you were to open a new window in your web browser today (19Aug13), go to www.natureserve.org, hit that “Explorer” button on the right panel, and execute a query for freshwater snails AND Delaware, the search engine will return a list of just eight species.

This is a peculiar list.  Missing from it are the four most common gastropod species actually inhabiting the freshwaters of Delaware: Physa acuta (aka P. heterostropha), Menetus dilatatus, Ferrissia fragilis, and Lymnaea (Pseudosuccinea)columella.  All four of these species are very nearly cosmopolitan in their distribution throughout eastern North America, and simple reference to the collections of either the DMNH or the ANSP would have returned numerous Delaware records for most of them.

The NatureServe report will also include one species that our extensive field surveys of Delaware and attendant reviews of systematic collections have failed to uncover, Physa gyrina.  Populations of Physa gyrina do inhabit Ridley Creek in Delaware County, southeastern Pennsylvania, so on first reading it certainly seems possible that the NatureServe record might be bona fide.  Or might this record represent a misidentification of Physa acuta?  The DMNH collection does hold a single undated lot of P. acuta (locality just “Wilmington”) misidentified as P. gyrina.

On 28July13 I sent an email inquiry to Dr. Bruce Young, Director of “Species Science” for NatureServe, asking if he could provide a reference supporting his report of P. gyrina in Delaware.  Dr. Young replied the next day, apologizing that “for common species we do not tie specific records to individual references or museum collections.”  Ms. Margaret Ormes of NatureServe followed up with “I just looked at our database and my best guess is that it was added (as Physella gyrina) based on Burch (1989).” [1]

I do appreciate the courtesy of the NatureServe staff, but the facts are very plain and very ugly.  The mission of NatureServe is advocacy, not science, and Physa gyrina is a trash snail, and they do not care whether arbitrarily-chosen trash snails actually inhabit arbitrarily-chosen states.  The NatureServe Explorer database is a smokescreen and a ruse, designed to lend false scientific credibility to a political agenda.

Science is the construction of testable models about the natural world.  Such models need not necessarily be accurate, nor even based on reliable data.  I am not fussing here about the discrepancy between the NatureServe estimate of 8 freshwater gastropod species in Delaware, and the FWGNA estimate of 20.  Nor am I fussing about the basis of the NatureServe estimate, which is spurious.

Science will fix these things, eventually.  There are scientists who will drive 16,139 miles in a 1992 Nissan pickup, camp in the rain, and eat Dinty Moore beef stew for a week to not find Physa gyrina in Delaware.  There are scientists who will dump three years of unsorted DNREC-DWR macrobenthic samples into little Petrie dishes and squint through microscopes for hours to not find Physa gyrina in Delaware.  There are scientists who will sleep five nights on an air mattress in Alexandria to ride the orange line downtown to pull every drawer of physids out of the US National Museum to not find Physa gyrina in Delaware.  Science ultimately fixes carelessness, sloppiness, and neglect.

No, the worst thing about the Explorer database is not that it is wrong, but that it reinforces conventional ignorance, and in so doing works against the cause we all seek to advance.  Fresh young students, casting about for research ideas, will tend to assume that the freshwater gastropod fauna of North America is in some sense “known,” and divert their energies elsewhere.  A proposal to the NSF Biotic Surveys and Inventories Program will be reviewed more favorably if it is directed toward the Ubangi River than to the Nanticoke, even though the freshwater gastropod fauna of the Ubangi is better documented [2].  Reinforcement of conventional ignorance is not the main problem I have with the NatureServe organization [3], but it is certainly in the top ten.

How big is your budget, Dr. Young, and how large is your staff?  The FWGNA project has now surveyed all or part of ten states.  This we have done with no more than $5K in grant support total, over 15 years.  Those 16,139 miles we drove in 2012-13 were unreimbursed.  We have paid $49/night out of our own pockets to sleep on air mattresses in Alexandria.  We bought our own Dinty Moore.

I will end this essay, however, on a note of hope.  Despite the layers of pseudoscientific hoo-hah in which NatureServe cloaks its Explorer website, it remains just a website, run by a political advocacy group.  And (how many times must we warn our students?) the internet is a wild and woolly marketplace of information, both the good and the bad, and the buyer must beware.  Each report returned by the NatureServe Explorer comes with the following disclaimer: “All documents provided by this server are provided “as is” without warranty as to the currentness, completeness, or accuracy of any specific data.”  In the final analysis, the Explorer database is not peer-reviewed science, and it does not pretend to be.

Thank heaven no legitimate researcher would ever confuse spurious data made available from the website of an advocacy group with reliable science.  Thank heaven.

Notes

[1] Yes, it does seem plausible to me that the initial state-by-state freshwater gastropod distributions uploaded to the NatureServe Explorer may have been the work of some intern hired to extrapolate the broad ranges found in J. B. Burch’s North American Freshwater Snails.  Burch lists 15 subspecies of P. gyrina, the ranges of at least two of which certainly include Delaware.  The range of Physella gyrina aurea is given as “New Jersey to Kansas, south to Arkansas and Florida,” and that of Physella gyrina cylindrica is given as “Ontario and New York south to Virginia.”  Then did our young intern simply miss Delaware when extrapolating “New England to Ohio, Tennessee and the Virginias” for P. heterostropha?  And did that intern miss Delaware when extrapolating “Eastern United States, from Maine west to Iowa, south to Texas and Florida” for Menetus (Micromenetus) dilatatus?  And so forth?  The entire enterprise is a house of cards.

[2] Brown, D. S. (1994)  Freshwater Snails of Africa and their Medical Importance (Second Edition).  Taylor & Francis, London.  608 pp.

[3] My main problem with NatureServe is the pseudoscientific method by which they gin up “conservation status ranks.”  See:

• Toward the Scientific Ranking of Conservation Status [12Dec11]

Pomacea News

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019d)  Seven dispatches from the Pomacea front.  Pp 19 - 28 in The Freshwater Gastropods of North America Volume 4, essays on Ecology and Biogeography.  FWGNA Press, Charleston.

The rate of scientific advance on the invasive species front always seems to far outstrip the (rather languid) research progress we seem to log on any of our native freshwater gastropod fauna.  Thus it has become our occasional custom to publish batches of news to catch us up on particular invasive species, bundled for convenience.  So here, for the general edification of the readership, are four news items featuring Pomacea.

Clarifying the Identities

A laurel, and hearty thank-you are due to our friend Ken Hayes and his colleagues at the University of Hawaii (and elsewhere) for their contribution published late last year in the Zoological Journal of the Linnean Society, “clarifying the identities of two highly invasive Neotropical Ampullariidae” [1].  This is research from the old school, emphasizing comparative anatomy, histology, biogeography, and traditional taxonomic scholarship to resolve a problem that has bedeviled the Pomacea community for 200 years, both North American and South.  I am persuaded that the most common invasive species here in the southeastern United States is best identified as Pomacea maculata (Perry 1810), rather than P. insularum (d’Orbigny 1835) as most workers have previously supposed, and have updated the FWGNA page accordingly [2].

Ken’s primary focus is the distinction between P. maculata (previously insularum) sampled from Florida and the other common invasive species of global import, Pomacea canaliculata, sampled from Hawaii.  If I have any quibble with his study [3], it would be that no mention is made of P. canaliculata in Florida, which leaves me wondering about the reliability of reports by Florida natural resource agencies [4] that both species co-occur widely in The Sunshine State.

And do P. maculata and P. canaliculata hybridize?  In the final paragraph of their discussion Hayes and colleagues mention “possible hybridization events,” although we are offered no details.  Then what is the basis of the reproductive isolation between them?  There have been several nice descriptions of mating behavior and sex pheromones in Pomacea [5] – mate choice tests would appear to be low-hanging fruit.  Any students out there looking for a good thesis research topic?

Modeling the Invasion

Kudos are also due to Jeb Byers and his colleagues at the University of Georgia for their paper published in PloS ONE this past February, “Climate and pH predict the potential range of the invasive apple snail (P. insularum) in the southeastern USA” [6]. 

Jeb based his model on Pomacea records from the USGS Nonindiginous Aquatic Species Database (accessed in late 2009) cast onto a presence/absence grid of 1x1 km plots.  The (N=68) such plots where invasive Pomacea was present were primarily Floridian, but extended into six other states: TX, LA, MS, AL, GA and SC.  Jeb and colleagues also pre-screened 19 climate variables from BioClim to pick two of temperature and three of rainfall, and downloaded pH data from the USEPA Storet database.

The weakness of inferences based on any such model are fairly obvious – if the vast majority of the 1x1 km plots are suitable, but still have no invasive Pomacea, how strong can be the inference on absence?  But I do think the author’s prediction that the pH may prove too low for Pomacea in the Okefenokee Swamp should be robust, which is good news.

Dispatches from the Front

And indeed, our good friend Maj. Alan Covich has just returned from a scouting expedition to the Okefenokee Swamp at the head of a large detachment from the Society for Freshwater Science.  No enemy activity is reported in the area.

Meanwhile, reports from the Department of South Carolina are mixed.  On the positive side, the northernmost population of Pomacea does not seem to have advanced beyond its beachhead at Socastee [7].  A colleague and I canoed the Intracoastal Waterway downstream from the site of introduction last summer, finding no evidence of Pomacea at any point in our trip.  It was our impression that the habitat may prove unsuitable. 

The tidal fluctuation in the Intracoastal Waterway at Socastee is at least two feet (as witnessed from the photo below) to which one must add over a foot of slosh for the wake of passing motorboats.  The water is quite darkly stained and the cypress canopy generally dense throughout the shallows, both of which tend to keep aquatic macrophytes at negligible densities.  We simply did not see much food or habitat for Pomacea in that particular part of the world.

On the negative side, however, the Socastee population itself still appears quite healthy in the weedy ponds and ditches where it was first reported in 2008.  This despite the fact that the winter of 2009-10 was one of the coldest recently experienced in South Carolina [8], with a low of 18 degrees F recorded on January 11 at Conway, 10 miles to the north.  From the standpoint of climate, I am afraid that Jeb Byers’ map may prove a robust predictor, as well.

 

And also on the negative side, in August of 2010 word reached us of a second introduction in South Carolina, this at Lake Marion just south of the I-95 bridge.  Our friend Larry McCord of Santee Cooper (the utility that administers the lake) reported that “the population has been treated with a low level of copper in hopes to avoid spread to other areas.” 

With large populations of invasive Viviparus georgianus, V. subpurpureus [9], and Bellamya japonica jostling each other for grazing room on its dense beds of Corbicula, Lake Marion was already wearing the yellow jersey in this year’s “Tour de Malacological Infestation.”  Now Pomacea is threatening to eat all the invasive waterweed as well.  Bummer.

Poisonous eggs

I long ago ceased trying to understand why particular odd little snippets of scientific trivia find their way into the popular press.  But in early June a PLoS ONE paper by M. S. Dreon and an international team on toxic Pomacea eggs [10] was selected for feature by the AAAS online organ “Science Now" [11] and then propagated around the world by e!Science News, Reddit, Facebook, and what have you.

The “hook” used by Science Now was that the composition of Pomacea egg neurotoxin is “unusual for animals” and that “the apple snail creates it in an unprecedented way.”  But were I the editor of some popular science outlet, or indeed one of the authors trolling for popular attention and looking for bait, I would have emphasized the weirdness that any toxin should be found in any egg at all.

Embryos are edible.  Somewhat counter to the statement of Dreon and colleagues that “many invertebrates defend their eggs by endowing them with deterrent chemicals,” across all of evolutionary biology, plants and animals alike, the phenomenon is stunningly rare [12].  It is easy to observe that a mother-ampullariid must value her (relatively large) eggs much more highly than a mother-physid or a mother-pleurocerid, but when we expand the comparison to a mother-hen, a simple adaptationist explanation becomes more difficult to sustain.  Although Orians & Janzen punted their original 1974 article with “it is possible to be toxic if one is an embryo, but under most circumstances it isn’t worth the price,” they ultimately concluded, “We think that refining this answer is worth the price.”  Are we any closer to refining this answer if, now 40 years later, we have forgotten the question?

Notes 

[1] Hayes, K. A., R. H. Cowie, S. C. Thiengo, and E. E. Strong (2012)  Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda).  Zool. J. Linn. Soc. 166: 723-753.

[2] The (revised) Pomacea maculata page on the FWGNA site [html]

[3] Actually, it would appear that I have listed more than one quibble above.  And add this nasty clinker from page 744, “Molecular data confirm that P. maculata and P. canaliculata are two distinct species.”  Hayes and colleagues are referring to mtDNA sequence divergence here!  Good grief.

[4] Florida Fish & Wildlife Commission.  “Non-native Apple Snails in Florida.” [pdf]

[5] Takeichi, M., Y. Hirai & Y. Yusa (2007)  A water-borne sex pheromone and trail following in the apple snail, Pomacea canaliculata.  J. Moll. Stud. 73: 275-278.

Burela, S. & P. R. Martin (2011)  Evolutionary and functional significance of lengthy copulations in a promiscuous apple snail, Pomacea canaliculata (Caenogastropoda: Ampullariidae).  J. Moll. Stud. 77: 54-64.

[6] Byers, J., W. McDowell, S. Dodd, R. Haynie, L. Pintor, and S. Wilde. 2013. Climate and pH predict the potential range of the invasive apple snail (Pomacea insularum) in the southeastern United States. PLoS ONE 8: e56812. [html]

[7] Previous posts:

• Pomacea spreads to South Carolina [15May08]
• Two dispatches from the Pomacea front [14Aug08]

[8] See Figure 1 in this (weirdly related!) paper:

Dorcas, M. E., J. D. Willson & J. W. Gibbons (2011) Can Burmese pythons inhabit temperate regions of the southeastern United States?  Biol. Invasions 13: 793-802.

[9] Invasive viviparids in South Carolina [29Oct03]

[10] Dreon, M., M. Frassa, M. Ceolin, S. Ituarte, J-W. Qiu, J. Sun, P. Fernandez, and H. Heras. 2013. Novel animal defenses against predation: a snail egg neurotoxin combining lectin and pore-forming chains that resembles plant defense and bacteria attack toxins. PLoS ONE 8: e63782.  [html]

[11] ScienceShot: Invasive snails protect their young with odd poison. [html]

[12] Orians, G. H. & D. Janzen (1974)  Why are embryos so tasty?  American Naturalist 108: 581-592.

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.