Dr. Rob Dillon, Coordinator

Wednesday, August 8, 2018

Pleurocera alveare: Another case of CPP?

As of 2018 three cases of cryptic phenotypic plasticity (CPP) have been documented in the pleurocerid fauna of eastern interior drainages: the Pleurocera acutocarinata/clavaeformis/unciale group [1], the Pleurocera pyrenellum/acuta/canaliculata group [2], and the Pleurocera semicarinata/livescens/obovata group [3].  We have also speculated on this blog [4] regarding a similar situation in the Pleurocera carinifera/vestitum/prasinatum/foremani populations of the Coosa River.  A correlation between shell robustness and stream size seems quite general in pleurocerid populations throughout North America, does it not?

One of the main lines of evidence by which all these cases were recognized has been a concordance between the distributions of upstream and downstream taxon sets.  So, for example, in the Tennessee drainage the distribution of (nominal) P. pyrenellum in small creeks corresponds closely with the distribution of P. canaliculata in the main river.  The easternmost edge of the pyrenellum range is approximately the same as the easternmost edge of canaliculata, both right around Knoxville.  Given the continent-scale distributions of all three taxa in the group, canaliculata, acuta, and pyrenellum, such concordance hardly seems like a coincidence.

Pleurocerid populations bearing shells with the robust, triangular, gnarly phenotype identified as “Pleurocera alveare (Conrad 1834)” are, or at least were, widespread throughout many of the largest rivers of the US interior.  A quick search of the online Global Biodiversity Information Facility [5] returns 408 occurrences, of which 156 are georeferenced, primarily in the Cumberland, the middle Tennessee, the Green, and the main Ohio Rivers, plus the White River of Arkansas.  GBIF records any younger than 1955 total just 11, however, almost entirely in the Cumberland.  And I have exactly two modern records in my FWGO database.  Pleurocera alveare is nowhere near as common today as the world thinks that it is [6].

Historically, big-river populations of Pleurocera alveare bore shells like figure A above, from an undated lot in the US National Museum, locality given simply as “Kentucky.”  The shells look a bit like the ornately robust populations of Pleurocera canaliculata still widespread in big rivers of the Ohio drainage today, but the costae around the apex are distinctive.  The specimen depicted in Figure B above was collected by our good friend Martin Kohl from the Cumberland impoundment known as Dale Hollow Lake in 2006.

Pleurocera laqueata (Say 1829) is a common inhabitant of creeks and small rivers of the lower Ohio river system through the Green, Cumberland, and Tennessee drainages of Kentucky, north Alabama, and Tennessee west of Chattanooga.  The shells born by P. laqueata populations in small streams are slender and characterized by costae on the upper whorls (Figure D above), becoming broader and more robust in medium-sized rivers, such as the Duck (Fig C).

Sampling east across Tennessee, the observation that P. laqueata populations disappear from small streams at Chattanooga, exactly where P. alveare historically disappeared from the main Tennessee River, is striking.  And the gradients in shell morphology demonstrated by P. laqueata populations inhabiting long, gradually-growing reaches such as that in the Duck River, and the Obey River of the Cumberland, remind me very much of the P. canaliculata gradient we documented from the Wabash in 2013 [2].

It seems quite likely to me that populations long identified as “Pleurocera alveare” constitute another demonstration of cryptic phenotypic plasticity, Say’s (1829) nomen laqueata taking priority over Conrad’s (1834).  But following FWGNA conventions [7], let’s save Conrad’s (1834) alveare as a subspecies, shall we? 

And no, let’s not send up any flares regarding the apparent rarity of P. laqueata alveare in the big rivers of the central and southern United States today.  I simply do not think that robust, gnarly shell phenotype, no matter how striking, is heritable.


[1] Dillon, R. T. (2011) Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque 1818). Malacologia 53: 265-277. [PDF]  For more, see:
  • Goodrichian Taxon Shift [20Feb07]
  • Goodbye Goniobasis, Farewell Elimia [23Mar11]
[2] Dillon, R. T., S. J. Jacquemin & M. Pyron (2013) Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117-127.  [PDF]  For more, see:
  • Pleurocera acuta is Pleurocera canaliculata [3June13]
  • Pleurocera canaliculata and the process of scientific discovery [18June13]
[3] Dillon, R. T. (2014) Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata.  Zoological Studies 53:31. [PDF]  For more, see:
  • Elimia livescens and Lithasia obovata are Pleurocera semicarinata [11July14]
[4] For more about cryptic phenotypic plasticity in the Mobile Basin, see:
  • Mobile Basin III: Pleurocera puzzles [12Oct09
[5] For more on the GBIF, see:
  • Freshwater Gastropod Databases Go Global! [26May09]
[6] The IUCN lists Pleurocera alveare as “vulnerable,” the middle level in their ridiculous five-rank redlist system (least concern, near-threatened, vulnerable, endangered, critically endangered).  It was situations like this, where museum records dramatically overestimate modern abundance, that initially drove the FWGNA project back in 1998.

[7] For more on the subspecies concept:
  • What is a subspecies? [4Feb14]
  • What subspecies are not [5Mar14]

Wednesday, July 11, 2018

Twenty Years of FWGNA

The environmental movement has ever been riven with fad and fashion, wailing and rending our garments over the crisis of today, yesterday’s forgotten and gone.  Who among us remembers the Spotted Owl?  Who remembers the National Biological Survey?  I thought not.

Bill Clinton took office in January of 1993.  And high on the radar of his new Interior Secretary, Bruce Babbitt, was the Spotted Owl controversy, pitting the big lumber interests of the Pacific Northwest against advocates for an endangered bird.  Secretary Babbitt embraced the idea of a “National Biological Survey” as a way to prevent, or at least manage, such problems in the future [1].  Presumably, if we could identify, count, and map every plant, animal, protozoan and algal cell in The Land of the Free and The Home of the Brave, we could see this sort of problem coming.

First FWGNA flier, 1998
In retrospect, Sec. Babbitt’s idea was dead aborning [2].  Congress allocated no new funds for the agency, and the political climate turned hostile almost immediately, with the Republican landslide of November 1994.  Secretary Babbitt staffed his new National Biological Survey with existing personnel, robbed primarily from the Fish & Wildlife Service.  The agency was subsumed under the USGS as the “Biological Resources Division” in 1996 and ultimately disappeared [4].

But it was against this backdrop that the Freshwater Gastropods of North America Project was born.  To us, the time seemed ripe for a “long-term, collaborative effort to inventory and monograph all freshwater snails inhabiting the continent north of Mexico.”  And where better to inaugurate such an effort than in Washington, DC?  The first “interest group” meeting of the FWGNA Project was held July 29, 1998, on the campus of George Washington University, as the American Malacological Society hosted the first World Congress of Malacology.

The FWGNA Project was initially coordinated by a board of eight “Regional Editors”: Steve Ahlstedt, Ken Brown, Rob Dillon, Paul Johnson, Eileen Jokinen, Bob McMahon, Dave Strayer, and Shi-Kuei Wu, jointly submitting a proposal to the NSF Biotic Surveys and Inventories program in November of 1999.  That proposal was revised and resubmitted in the fall of 2000, minus Shi-Kuei Wu (who had retired), but adding Bob Hershler, Rudiger Bieler, Jean-Marc Gagnon, Rob Guralnick, and Tom Watters.  Phase 1 of our proposed FWGNA Project was designed as a survey of museum holdings, with field surveys to follow in Phase 2 and taxonomic revisions in Phase 3.  Alas, the project was not funded.

Meanwhile, completely separate and independent of all the FWGNA excitement, the Freshwater Mollusk Conservation Society was born.  I was invited to a board meeting in Chattanooga in November of 1998 to draft bylaws for the new organization and asked to serve as chairman pro tempore of the FMCS Committee on the Status & Distribution of Gastropods.  My formal election to that post occurred in March.

So that first meeting of the FMCS Gastropod Committee, held on March 19, 1999, was synonymous with the second meeting of the FWGNA Project.  And our third meeting was also synonymous with the FMCS Gastropod committee meeting of March 14, 2001, at Pittsburgh.  Discussion at both of those meetings was about evenly split between a continental survey of freshwater gastropods and a “national conservation strategy,” being spearheaded by Paul Johnson.  Dr. Johnson succeeded me as chair of the FMCS Gastropod Committee in 2003.

Meanwhile, I had been elected to the presidency of the American Malacological Society.  And the featured symposium at the 2002 AMS meeting in Charleston was “The Biology and Conservation of Freshwater Gastropods” [5], with a fourth meeting of the FWGNA Project following on the evening of August 4.

At our 2002 meeting the idea of a “new model” for the FWGNA Project was born.  The project was to be decentralized as much as possible, with regional or local surveys conducted, and local sources of funding sought.  The effort would be united by a single database, in a common format, held centrally.  But otherwise, efforts would proceed independently.

FWGNA Logo 1999 - 2004
I don’t remember when the idea of an FWGNA website first came up.  I began posting resources and archiving old email messages at cofc.edu/~dillonr in early 1999.  But our first regional website, with a photo gallery, dichotomous key, and 24 species pages featuring distribution maps and biological information, was the Freshwater Gastropods of South Carolina, which went online in February of 2004, coauthored by RTD and T. W. Stewart.

We migrated over to cofc.edu/~fwgna in September of 2006, adding an FWGNC site for the Atlantic drainages of North Carolina, with Stewart and B. T. Watson.  An FWGGA for the Atlantic drainages of Georgia (with Stewart and W. K. Reeves) followed in March of 2007.  Our FWGVA site for the Atlantic drainages of Virginia (with Stewart and Watson) was under construction as early as December of 2006 but did not formally open until June of 2008.  The format for all four of these regional sites was designed by Ms. Jasmine Wu, a college friend of my daughter’s with good technical skills and a fine eye.

In late 2009 we purchased the domain name fwgna.org and embarked on a significant design upgrade, spearheaded by my good buddy and long-suffering Web Wizard, Mr. Steve Bleezarde.  Steve also suggested that I migrate from emailing an ever-growing address book [6] monthly news bulletins to posting essays in a blog format.  The “Grand Opening” of the FWGNA Blog was on February 28, 2010.

Our FWGTN East Tennessee site (with Martin Kohl) went online in November of 2011, and our FWGMA Mid-Atlantic site (with M. J. Ashton and T. P. Smith) went up in October of 2013.

Through our first 18 years, as we were hosted by the College of Charleston, I suppose the best descriptor for the FWGNA would have been, “Lightly-funded Extramural Research Project.”  We did receive a few small grants, most notably from the U.S. National Park Service, the Virginia Department of Game and Inland Fisheries, and Normandeau Associates.  But our income was always far, far below our expenditures.  I’d estimate that 95% of the work has been done for love, not money.

I was banned from the campus of the College of Charleston in 2016, forced into retirement, and sued [7].  That lawsuit was settled late last year [8].  And I have now used the proceeds therefrom to establish the FWGNA Project as a sole-proprietor consultancy.

So, what does the future hold?  When field conditions are good, we have been working in the Ohio River drainages of western Pennsylvania, West Virginia, Ohio, Kentucky, Indiana, and eastern Illinois.  The big team of RTD, Kevin Cummings, Ryan Evans, Mark Pyron, Tom Watters, Will Reeves, Richard Kugblenu, Jeffrey Bailey and Michael Whitman have developed a database of 5,256 freshwater gastropod records at last count, comprising 68 species and subspecies.  A 2017 PowerPoint presentation describing last spring’s 4,746-record “interim report” is downloadable from the link below.  And a draft “Freshwater Gastropods of The Ohio” website should appear online before the year is out [9].

FWGO ppt from SFS 2017
When field conditions are inclement, as they have been all over The East for months now, we have been working on the first hardcopy publications of the FWGNA Project.  A four-volume set should hit the market in the next couple months, Good Lord willing, and the creeks do rise.  Volume I, by Dillon, Ashton, Reeves, Smith, Stewart & Watson will report the scientific results of our 12,211-record freshwater gastropod survey of the Atlantic drainages, from Georgia to the New York line.  Volumes II, III, and IV will collect, reorganize, edit and update a diverse assortment of approximately 100 essays that yours truly has emailed or posted on the FWGNA blog since 2006.  You won’t want to miss any of that.

I should conclude by re-emphasizing the collaborative foundation of the FWGNA Project.  I realize that our recent evolution into a sole-proprietorship makes it look as though I, your Coordinator, am somehow angling to become Your Boss.  I have fought that perception as hard as I can for 20 years, and will continue to resist it until we all, together, cover this great wide continent of ours, Sea to Shining Sea.

Science is The Boss of the FWGNA Project.  I do, however, have a series of polite suggestions for everybody, independently, today.  Please walk out your back door, stoop down into that first little puddle, and note the remarkable freshwater gastropod fauna crawling lazily on the grass blades.  Take good data, collect if you hear the call, walk 50 yards, stoop over again, and repeat.  If you work for an agency, start a program.  If you’re a research scientist, write a proposal.  You do not now, nor have you ever been called to, clear anything with anybody, most especially me.  But again, please,

Keep in touch!


[1] Regional biological surveys have been around since natural history became a science.  And ideas for National Biological Surveys in the U.S. and Canada were being discussed in academic circles as early as the 1970s, continuing to gain momentum in the 1980s.  For more, see:
Wagner, F. H. (1999) Whatever happened to the National Biological Survey?  Bioscience 49: 219 – 222.

[2] But you’ve got to love it.  Here’s a quote from Krahe [3]:
“The NBS would parallel the U.S. Geological Survey (USGS) in its mission of collecting, analyzing, and disseminating scientific data without any entanglement in the regulatory and managerial responsibilities of its sister agencies. ‘What we are doing is strengthening the credibility of science, Babbitt said, by putting some distance between federal scientists and those in government who make policy and execute it.”
[3] Krahe, D. (2012) The Ill-fated NBS: A historical analysis of Bruce Babbitt’s vision to overhaul Interior Science.  Pp 160 – 165  In: Weber, Samantha (ed.) Rethinking Protected Areas in a Changing World: Proceedings of the 2011 George Wright Society Biennial Conference on Parks, Protected Areas, and Cultural Sites. Hancock, Michigan: The George Wright Society.

[4] Quoting the USGS website verbatim: “2010 – A USGS realignment established the Ecosystems Mission Area, which comprised the Fisheries, Wildlife, Status and Trends, Environments and Invasive Species Programs and the Cooperative Research Units, all former programs of the BRD.”

[5] The proceedings of the AMS2002 freshwater gastropod symposium were published in the American Malacological Bulletin, Vol 19(1/2).

[6] I did not, however, abandon my email address book, which has 264 entries at present.  Any of my readership who might wish to be added are cordially invited to email DillonR@fwgna.org.

[7] For a good review, see the August 8, 2016 issue of Inside Higher Ed: “Who Decides What Must Be on a Syllabus?” [html]

[8] Here’s a rather sweet-natured update published in the Charleston Post & Courier 26Feb18.  With video!  See “Scientist who had falling-out with College works from home.”  [html]

[9] The FWGNA Project is looking for a colleague with GIS mapping skills.  Any volunteers?

Monday, July 9, 2018

Potamopyrgus in New Jersey

Last Wednesday I received an email from Mike Cole of Cole Ecological, forwarded by our good buddy Tim Pearce.  Attached to Mike’s message was the JPEG below, from samples taken in the Musconetcong River of northwestern New Jersey, a tributary of the Delaware.  This is the third introduction of the New Zealand Mud Snail, Potamopyrgus antipodarum, confirmed for US Atlantic drainages.
From Mike Cole 4July18

We reported Potamopyrgus in Spring Creek, a tributary of the Susquehanna in central Pennsylvania, back in 2013, and the 2017 discovery in Maryland’s Gunpowder River just last month [1].  The Musconetcong, much like the Gunpowder and Spring Creek, is a lovely body of water, tumbling cold, clear and rich about 73 km through a surprisingly unspoiled valley.  Mike reports Potamopyrgus at five sites scattered along the lower 10 km of the river.

So NZMS were completely unknown in US Atlantic drainages until one day they popped up in the middle of Pennsylvania, and the next day they popped up in Maryland 50 km south, and the next day they popped up in New Jersey 200 km east.  What is going on here?

What the Musconetcong shares with Spring Creek and the Gunpowder River, in addition to NZMS introductions, is trout.  New Jersey Monthly counted the “mighty Musky” as “among the state’s most revered waterways, thanks to its ever-changing landscape and world-class fly-fishing [2].”  The river is stocked by NJ Fish & Wildlife biologists weekly in April and May, pretty much down its entire length.

My father and I used to enjoy a fair amount of trout fishing ourselves, when I was young.  Early in the spring… doggone that water was cold… we always wore hip boots.  And in fact, I’ve got at least two or three pair of boots hanging upside down in my storage room this morning.
My right boot toe

Almost all the hip boots and waders I’ve ever worn in my life had deep, heavy tread on the soles, into which mud was always caked.  But I never cleaned the soles of my boots… not in 50 years… never really thought about it.

We fishermen (and biologists) need to start thinking about it.  That mud in the soles of our boots has the potential to track a lot of hitch-hikers from one stream to the next.  And remember – Potamopyrgus are parthenogenic brooders.  There’s no such thing as “one.”  And there’s nothing to stop those critters from washing down into the Delaware River.  Darn it.


[1] Previous posts on Potamopyrgus:
  • Invaders Great and Small [19Sept08]
  • Potamopyrgus in US Atlantic drainages [19Nov13]
  • Invasive Species Updates [13June18]
[2] NJ Monthly, 19Mar14:
Gone Fishing: Musconetcong River [html]

Wednesday, June 13, 2018

Invasive Species Updates

Editor’s Note – Although it seems like we touch the subject almost every month, it has actually been almost five years since we rounded up the Pomacea news [1], and even longer for the other invasive gastropod species.  Six recent items of special interest are collected below.

Potamopyrgus in Maryland.  Early last September our good buddy Matt Ashton of the Maryland DNR sent me an email with a couple jpegs attached, including the photo below.  Matt was forwarding the report of a concerned citizen with very good reason to think he had discovered New Zealand Mud Snails in the Gunpowder River at the Prettyboy Dam tailwaters, about 30 km north of Baltimore.  See the 21Sept17 article in The Baltimore Sun from note [2] below for more details.

From Matt Ashton, MD-DNR
The Gunpowder is a lovely little river through most of its course, passing through four state parks on its 90 km journey from headwaters in southern Pennsylvania to mouth at the Chesapeake Bay.  In the late 1980s the Prettyboy Dam tailwaters were stocked with brown and rainbow trout, eggs and fingerlings as well as adults, and both populations have now become self-sustaining [3].  Attention from an avid community of fishermen has quite predictably followed.

This is the second population of Potamopyrgus antipodarium reported from a US Atlantic drainage.  My readership will probably remember the first report I posted back in November of 2013, from a small tributary of the Susquehanna River in central Pennsylvania, also heavily fished by trout anglers [4].  Spring Creek is perhaps 50 km north of the Gunpowder headwaters.  The implication would be that the little snails were transported from Pennsylvania to Maryland via muddy waders or bait buckets.

From the mouth of the Gunpowder to the heart of our nation’s capital is but another 80 km.  I understand that legislation has been introduced in Congress to build a big, beautiful six-inch wall from the Delaware River to the West Virginia line, with a three-inch guardhouse on the Baltimore/Washington parkway.

And (less surprisingly) in Syracuse.  The Great Lakes populations of Potamopyrgus are much older than the Atlantic populations; New Zealand mud snails were first reported from Lake Ontario as early as 1991 and Lake Erie in 2005.  So, surfing around in the USGS-NAS Nonindigenous Aquatic Species Database [5], I picked up a couple 2016 reports of Potamopyrgus in tributaries of Onondaga Lake, near Syracuse.

The Erie Canal runs from the eastern end of Lake Erie across the width of New York, intersecting Oneida Lake and the tailwaters of several of the Finger Lakes, as well as Onondaga Lake, to meet the Hudson River just north of Albany.  How long will it be until tired, poor Potamopyrgus are tempest-tossed down the Hudson into New York Harbor, to enter Ellis Island through the back door?  Is that one golden, too?

Pomacea progress.  As threatening as an invasion of 5 mm snails down from the north most certainly must be to homeland security, the threat posed by an army of 5 cm snails advancing up from the south is two orders of magnitude worse.  On the plus side, however, we are getting some very good science out of it.

In late 2015 our colleague Ken Hayes and 32 coauthors published a comprehensive review of the biology of the entire family Ampullariidae [6], broader than their systematic paper of 2012 [7] and better-integrated than the big 2006 book edited by Joshi & Sebastian [8].  More than just the economically-important pests and pets, the authors reviewed the entire scientific literature published on all 117 ampullariid species (by their estimate) in all 7 genera worldwide.

But though Ken and his colleagues cast their nets as broadly as possible, what they drew back was almost entirely Pomacea canaliculata.  They concluded with a call for additional research of a comparative nature, including behavioral studies that might reveal patterns that may have played a role in the evolution of the other 116 species.  We most certainly agree.

PhilRice II.  So speaking of Joshi & Sebastian.  Last year the Philippine Rice Institute published a second big collection of research focused on the Pomacea invasion, this volume with our good friend Rob Cowie among the editors [9].  A free pdf download is available from the link below.  

Fig. 7 of Rama Rao et al. [14]

Maculata/canaliculata hybridization.  Since the first appearance of pest Pomacea in North America, I have continued to be especially curious about reproductive isolation between populations of P. canaliculata and what is now called P. maculata.  So perhaps the most interesting Pomacea news in recent years, from my perspective, was the 2008 discovery that P. maculata has been introduced together with P. canaliculata throughout east and southeast Asia [10].

Apparently published a bit too late to be collected in the nets of Hayes and his 32 colleagues was an excellent 2013 study by Matsukura et al. documenting extensive hybridization between P. canaliculata and P. maculata throughout Japan, Korea, Vietnam and The Philippines [11].  Of the 16 populations sampled, 7 (all Japanese) were apparently pure canaliculata.  The remaining 9 were mixtures, including one population that was primarily maculata with a few hybrids, and one that was primarily hybrid, with a few pure maculata and canaliculata.

Even more interestingly, Matsukura performed a set of no-choice mating experiments between canaliculata and maculata, suggesting that F1 hybrid clutches suffer significant reduction in their hatching rates, from around 80% down to maybe 20% [12].

Pomacea release sex pheromones and demonstrate elaborate courtship behaviors, featuring nuptial gifts [13].  It would be tempting to hypothesize that some sort of prezygotic reproductive isolating mechanisms may have evolved in their native ranges, which have now broken down in Asian rice fields, as lions and tigers mate in zoos.  But in a surprise finish, Matsukura and colleagues also obtained a sample of 17 individual Pomacea from 5 sites in Argentina and discovered evidence of hybridization in ten of them!  Even in the home range.  Fascinating.

If maculata and canaliculata cannot tell each other apart, how can we?  Hayes et al. [7] observed that typical egg masses of P. maculata contain significantly more eggs of a significantly smaller size than P. canaliculata, a result that Matsukura and colleagues confirmed in Japan.  But that’s not terribly helpful with an adult in hand. 

So Hayes et al [7] also suggested a variety of distinguishing shell traits [14], including adult size, ratio of spire height to shell length, shell thickness, umbilicus, shouldering, and lip pigmentation.  But just last month Rama Rao and colleagues [15] published an interesting study of 130 Pomacea sampled from 8 populations in peninsular Malaysia, 5 of which turned out to be canaliculata/maculata mixtures, judging from CO1 sequence. 

Rama Rao and colleagues did not employ nuclear markers, and hence could not identify hybrids [16].  But judging from mtDNA haplotype, they selected 26 canaliculata and 26 maculata and performed an extensive series of shell morphological and morphometric analyses, including simple linear measures and ratios as well as the geometric analysis shown in the figure above.  They did discover a statistically-significant difference between the two groups in ratios of shell height to shell width and aperture height, but of such a fine nature as to be practically useless.  The bottom line is that the Pomacea of Malaysia seem to comprise one single heap of big slimy snails, darn near indivisible.

And meanwhile, in South Carolina.  Our colleague Elizabeth Gooding and six coauthors (including yours truly) have just published a statewide survey [17] for Pomacea at the highest latitudes of its current US range [18].  The Socastee/Myrtle Beach area [19] is on the northern tip of USDA cold-hardiness zone 8b, with average annual extreme minimums around 15 to 20 degrees F, or -9 to -6 degrees C.  We report both copulation and egg laying year-round, even in coldest months of winter [20].

I understand that legislation has been introduced in Washington to build a big, beautiful wall on the North Carolina line from Cape Hatteras to Tennessee, 50 feet tall by back-of-the-envelope calculation [21], Pedro himself manning the I-95 guardhouse just two mucus trails and one gigantic traffic jam North of the Border.


[1] My earlier Pomacea reviews include:
[2] Invasive New Zealand mud snails found in Gunpowder River. The Baltimore Sun 21Sept17.

[3] The situation is actually a bit more complicated.  The first 7.2 miles below the dam are managed as a wild trout stream, catch-and release.  Anglers in the next 4.2 miles can keep two trout/day.  And the next 6.1 miles are stocked in the spring and fall with ordinary hatchery-reared trout, creel limit five trout/day.  See MD-DNR-fisheries.

[4] For more about the discovery of New Zealand Mud Snails in central Pennsylvania:
  • Potamopyrgus in US Atlantic Drainages [19Nov13]
[5] For my reviews of state and national invasive species online databases, see:
  • To Only Know Invasives [16Oct15]
  • To Only Know Invasives in My General Vicinity [9Nov15]
[6] Hayes KA, Burks RL, Castro-Vazquez A, Darby PC, Heras H, Martín PR, et al. (2015) Insights from an integrated view of the biology of apple snails (Caenogastropoda: Ampullariidae). Malacologia 58(1–2):245–302.

[7] Hayes KA, Cowie RH, Thiengo SC, Strong EE (2012) Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda). Zool J Linn Soc. 166(4): 723–753.

[8] Joshi RC, Sebastian LS. (2006) Global advances in ecology and management of golden apple snails: Philippine Rice Research Institute (PhilRice), 600 pp.

[9] Joshi, RC, Cowie RH, Sebastian LS. (2017)  Biology and management of invasive apple snails.  Philippine Rice Research Institute (PhilRice) 406 pp.  [PDF]

[10] Hayes, K. A. et al. (2008) Out of South America: multiple origins of non-native apple snails in Asia.  Diversity and Distributions 14: 701-712.
Matsukura, K. et al. (2008) Genetic divergence of the genus Pomacea (Gastropoda: Ampullariidae) distributed in Japan, and a simple molecular method to distinguish between P. canaliculata and P. maculata.  Appl. Entomol. Zool. 43:535-540.

[11] Matsukura, K et al.  (2013) Genetic exchange between two freshwater apple snails, Pomacea canaliculata and Pomacea maculata invading East and Southeast Asia.  Biol. Invasions 15: 2039-2048.

[12] The hatchability experiment was not as neat as one might hope, and the results a bit ambiguous.  See the paper itself [10] for details.

[13] Burela S, Martin PR. 2009.  Sequential pathways in the mating behavior of the apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Malacologia 51: 157 – 164.
Burela S, Martín PR. 2011. Evolution and functional significance of lengthy copulations in a promiscuous apple snail, Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Journal of Molluscan Studies 77: 54–64.
Takeichi M, Hirai Y, Yusa Y. 2007. A water-born sex pheromone and trail following in the apple snail, Pomacea canaliculata.  Journal of Molluscan Studies 73: 275–278.

[14] There are also anatomical differences between canaliculata and maculata, most notably a difference in penial sheath.  A study of anatomical hybrids would be most salutary.

[15] Rama Rao S, Liew T-S, Yow Y-Y, Ratnayeke S (2018) Cryptic diversity: Two morphologically similar species of invasive apple snail in Peninsular Malaysia. PLoS ONE 13(5): e0196582.

[16] Back in the allozyme days, I could have solved that problem with one afternoon in the laboratory and $30 for reagents.  It does frustrate me that science often seems to lose good old technology in its restless quest for the new.

[17] This is the same survey of which I made passing mention in my essays of November and December of 2015.  Although we did not discover any Pomacea on Hilton Head Island, we do formally report invasive populations of Bellamya, Biomphalaria, Melanoides and Pyrgophorus in our 2018 paper [17].  To refresh your memory:
  • The Many Invasions of Hilton Head [16Dec15]
[18] Gooding, E. L., A. E. Fowler, D. Knott, R. T. Dillon, T. Brown, M. R. Kendrick, & P. R. Kingsley-Smith (2018) Life history and phenological characteristics of the invasive island apple snail, Pomacea maculata (Perry, 1810) in stormwater retention ponds in coastal South Carolina, USA.  Journal of Shellfish Research 37: 229 - 238. [PDF]

[19] Yes, the introduction of Pomacea we first reported from the Myrtle Beach area in 2008 may even be spreading.  I understand that the initial site of discovery around that trailer park in Socastee was treated with copper sulfate, but the snails seem to have jumped a couple km SE into ditches and stormwater retention ponds around a sprawl of strip malls and big-box retailers.  For ancient history, see:
  • Pomacea spreads to South Carolina [15May08]
  • Two dispatches from the Pomacea front [14Aug08
[20] Although no juveniles seem to hatch in the South Carolina winter.  One presumes that egg masses laid in the winter will hatch in the spring.

[21] If a 6-inch wall is sufficient to stop a 5 mm gastropod coming south between Baltimore and Washington, then to stop a 5 cm gastropod advancing north from the Carolinas we need 100 x 6 inches = 600 inches = 50 feet.

Thursday, May 10, 2018

Dichotomous Dichotomous Keys

Last month [1] we reviewed the Gastropoda chapter contributed by Christopher Rogers to the new Fourth Edition of Thorp & Covich’s Keys to Nearctic Fauna [2].  The bottom line was, “Buy this book.”  And among the several lines of support I offered for this recommendation was a somewhat enigmatic observation to the effect that the new fourth-edition dichotomous key complements, but is in many cases strikingly different from, the old third-edition key.  What did I mean by that?

In two words, Christopher’s new key is evolutionary, whereas the old one was ecological.  Christopher has divided the North American freshwater gastropods phylogenetically, designing his dichotomous key to branch as a phylogenetic tree might branch.  The older key divided the fauna functionally, according to morphological adaptation.

Broad/flat vs. Narrow/filiform, if you're curious...

 So, couplet #1 of the old Third Edition was a choice between “shell coiled” and “shell an uncoiled cone.”  The former choice took the user onward into the body of the key, while the latter choice immediately took the user aside to seven limpet genera.  Those seven limpet genera are assorted into three families: the Ancylidae with four, the Acroloxidae with one, and the Lymnaeidae with two.  This is an ecological distinction – the limpet shape demonstrating superior strength against predation, and superior performance against hydrodynamic drag, given a solid substrate upon which its bearer can graze.

That patelliform shape has, of course, evolved many, many times independently in many, many different gastropod lineages, both freshwater and marine [3].  And it has apparently evolved (at least) three times separately in the freshwater gastropods – in the Acroloxoidea, in the Lymnoidea, and in the ancylid taxa of the Planorboidea.

So Christopher elected to open his new Fourth Edition gastropod key with operculum present/absent as his couplet #1. This is the easiest character by which to distinguish pulmonates from prosobranchs, the primary phylogenetic division in the freshwater gastropod fauna.  All the freshwater limpets are pulmonates, missing an operculum, hence all go together to his couplet #7.  Then at Christopher’s couplet #7, the user finds: 
7(1) Shell not patelliform, or if patelliform, then spire sinistral (apex centered or to right of midline) and blunt, with adult patelliform shell larger than 7 mm … go to #8.
7’ Shell patelliform with spire dextral (apex to left of midline), acute; adult shell less than 7 mm in length … Acroloxidae.
So I understand what Christopher is trying to do here, and I appreciate his effort.  He is beginning to sort the pulmonate families using evolutionary distinctions.  But I’m just not sure it works.

First, as a practical matter, users cannot determine if the spire is sinistral or dextral for 99.999% of all the limpets in the creek – they’re blunt and smooth.  So, users must read over that text to “apex centered or to the right of midline” vs. “apex to left of midline.”  And second, being finely evolutionary, both Acroloxus and the lymnaeid limpets (Lanx and Fisherola) demonstrate shell apexes to the left of midline, at least when young [4].

Now I understand if Christopher does not want to engineer his dichotomous key to the entire freshwater gastropod fauna of North America around an accommodation for juvenile-Lanx-collectors.  So I’ll let it go.  Let’s suppose we have under our scope some non-patelliform pulmonate, like Physa or Helisoma.  And we have dodged through couplet #7 to arrive at couplet #8, undiscouraged.  Here we read: 
8(7) Tentacles narrow, filiform …. 9
8’ Tentacles broad, flat, triangular; haemoglobin absent; coiled shell always dextral, patelliform shell with apex central or sinestral [sic]; never planospiral … Lymnaeidae
For heaven sake!  Now Christopher seems to expect us to have a living animal under our scope, or at least a very well-preserved one, to distinguish narrow tentacles from broad tentacles?  Narrow compared to what?  There’s no tentacle figure.  Haemoglobin, are you serious?  Must I medevac this little speck of coiled brown nothing to England and set up an IV?  Typed and cross-matched, stat?

In the Third Edition key, after I had observed that my Physa was coiled and been directed to couplet #8, I was next asked if the shell was planospiral or “with raised spire.”  If planospiral go to Planorbidae, otherwise go on to couplet #20.  Simple.

I am not going to criticize every couplet in Christopher’s entire 20-page key.  It’s a tremendous effort, and I don’t want to diminish his contribution.  I will simply observe that the evolutionary approach taken in the Fourth Edition is not as user-friendly as the ecological approach taken in the third.

So, here’s the bottom line for this month’s essay.  Don’t throw away your old Third Edition of Thorp & Covich.  Open it up on the lab bench next to your new Fourth Edition and use both simultaneously.  The two works side by side are a dichotomous perspective on the wonderful diversity that marks the North American freshwater gastropod fauna.


[1] REVIEW: Thorp & Covich Fourth Edition [12Apr18]

[2] Thorp, J. H., and D. C. Rogers (2016) Keys to Nearctic Fauna.  Thorp and Covich’s Freshwater Invertebrates, Fourth Edition.  Volume II.

[3] Actually, the “hypothetical ancestral mollusk,” from which all sevenish of the molluscan classes diverged back in the Precambrian, is generally modelled with a limpet-like (or plate-like) shell similar to that borne by the present-day Monoplacophora.

[4] Basch, P. (1963) A review of the recent freshwater limpet snails of North America. Bull. Mus. Comp. Zool. Harvard 129: 399-461.

Thursday, April 12, 2018

REVIEW: Thorp & Covich Fourth Edition

Thorp, J. H., and D. C. Rogers (2016) Keys to Nearctic Fauna.  Thorp and Covich’s Freshwater Invertebrates, Fourth Edition.  Volume II.

“What a marvelous contribution!  I never thought I would live to see the day.”

Both these sentiments oscillated through my mind in rapid succession as I flipped through the pages of Christopher Rogers’ “Class Gastropoda” key in the new edition of Thorp & Covich displayed on the auction table in Raleigh [1] last June.  The taxonomy is complete, thorough, well-researched and modern.  Just three genera of living pleurocerids, check.  Hubendick’s single, broadly-inclusive genus of lymnaeids, check.  Just two genera of physids, check!  Bellamya yes, Planorbella no.  Onward as the pages turned.  What a marvelous contribution!  I never thought I would live to see the day.

This was not the first time such thoughts had flickered through my mind, however.  It had happened twice before.

I imagine that most of my readership will be familiar with the Thorp & Covich tradition.  The first edition of Ecology and Classification of North American Freshwater Invertebrates, as the collaboration was originally called, was published in 1991, with a second edition in 2001 and a third in 2010.  Over this 20-year span Thorp & Covich has become the primary bench reference for biologists working with the (non-insect) freshwater macrobenthic fauna of the United States [2].

Ken Brown was the solo author of the Gastropoda chapter through its first two editions, Chuck Lydeard joining him in 2010 [3].  Ken has an excellent background in freshwater gastropod ecology, which together with anatomy, physiology and (later) gene trees comprised the first 70% of the chapter.  The remaining 30% was allocated to a dichotomous key following the taxonomy of Burch [4] rather closely [5], but I am not criticizing.  That’s all there was.

So the first time that “marvelous-contribution-but-it’ll-never-happen” thought flickered through my brain was in March of 2011, when I opened an email from Jim Thorp.  Jim intimated to me that, even though his third edition was only a single year off the press, he and Christopher were already making plans for a major revision.  He projected that his fourth edition would expand into a series of volumes, the first of which would be dedicated to more ecological themes, the second of which would present dichotomous keys to the Nearctic fauna, the third to the Palaearctic, and so forth [6].  The fourth-edition keys would be much larger and more detailed than those of the third edition, extended down to the species level wherever possible.  And he wanted me to lead the Nearctic Gastropoda team.

I was flattered, of course.  But the series of negotiations into which we entered did not ultimately yield fruit.  I am a big fan of review and synthesis, and I greatly appreciate the value of reference works like Thorp & Covich for biologists in the field today.  But I climb onto the shoulders of giants with a pair of binoculars looking up, not down.  An historian I am not.

So for example, of the roughly 150 nominal species of pleurocerid snails Calvin Goodrich recognized in North American fresh waters [7], forwarded to the present day by Burch, I should estimate that no more than about 30 – 40 are biologically valid.  How am I to construct a dichotomous key to such a biota, I asked Jim, if most of the taxa to be keyed are not legitimately distinguishable?  Could I synonymize?

Jim (quite understandably) demurred.  Christopher suggested that, in cases such as the Pleuroceridae, I simply key down to the lowest firm taxon and drop it, with some language to the effect that “This genus is in need of revision and therefore identifications are left at genus level.”  Well, I thought to myself, all the North American freshwater gastropod genera are in need of revision.  Most have never had a vision in the first place.  Ultimately, I found it impossible to rationalize the expenditure of my own time and effort unless I could move the ball forward [8].

So Volume 1 of the Fourth Edition appeared in 2015, our good friend Mark Pyron’s name appearing above that of Ken Brown as author of Chapter 18, “Introduction to Mollusca and the Class Gastropoda.”  I was pleased to see that the Pyron & Brown contribution extended to 41 pages, up from the 30 pages of the 1991 original.  And sure enough, those 41 pages were focused entirely upon ecology and evolution, no dichotomous key anywhere in evidence.

And the second time that “marvelous-contribution-but-it’ll-never-happen” thought flickered through my brain was later that same year, when Christopher emailed me to request that I review the dichotomous key he himself had prepared for Volume 2.  His draft looked excellent – I really didn’t have a whole lot of suggestions to offer.  In retrospect, I think that from among the entire 3 x 10^8 population of the United States of America, I might have been the worst possible choice to review a freshwater gastropod key.  Because I understood what Christopher was trying to say, and I often skipped ahead, knowing where he was trying to go.

Regarding the problematic groups, I was gratified to see that Christopher had taken the approach he had first advocated during our 2011 negotiations.  Here’s a verbatim quote from his section entitled Limitations: 
“Particularly vexing is the strange confusion in the taxonomic literature, with many taxa accepted or rejected without explanation, and good quantitative taxonomic revisions ignored without explicit justifications.  Because of this issue, the keys are taxonomically conservative, often terminating with species groups rather than species.”
 So Christopher judged such terminations to be necessary for 13 “species groups” in the Nearctic freshwater gastropod fauna all told: the hydrobioid genera Amnicola, Lyogyrus, Clappia and Fluminicola, the hydrobioid families Cochliopidae and Hydrobiidae (ss), assorted prosobranch genera Valvata, Campeloma, Pleurocera/Lithasia, and Leptoxis, and the planorbid genera Helisoma, Carinifex, and Menetus.  Fine.  It’s hard to know which of those thirteen groups is the biggest mess.

The rest of the freshwater gastropods of North America Christopher did, very bravely, key all the way down to the species level.  Among the pulmonates he recognized 10 species of Lymnaea, 9 species of Physa, and 24 species of (non-Helisoma, non-Carinifex, non-Menetus) planorbids [9].  All good estimates – probably pretty close.  From among the entire 3 x 10^8 population of the United States of America, I may well appreciate the effort that Christopher must have put into this contribution the most.

So buy this volume.  Actually, you should back up and buy Volume 1 if you haven’t already, as well as Volume 2.  Do it for three reasons.  First, the gastropod taxonomy is correct, complete, and current.  Second, the new fourth-edition keys complement, but in many cases are strikingly different from, the old third-edition keys.  We’ll develop that theme next time.  And finally, assuage my guilt.  In retrospect, I may have been more a hindrance than a help to Christopher as he labored over this marvelous contribution.  I never thought I would live to see the day.


[1] SFS Raleigh  [4Apr17]

[2] Pennak held that position when I was coming up through the ranks, and is still an excellent reference.  Nothing in the essay above is intended to take anything away from Doug Smith’s (2001) Fourth Edition of “Pennak’s Freshwater Invertebrates of the United States” at all.

[3] Alan Covich and Ken Brown asked me to help with the 2010 edition.  I was flattered, but ultimately declined, for reasons similar to the ones I gave Jim Thorp in 2011.  I can be a difficult person to deal with.

[4] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI). 

[5] The hydrobioid subfamilies were raised to the full family level in the third (2010) edition.

[6] Twelve volumes are now on the drawing board, according to a more recent communication I enjoyed with Jim.  Volume III is now Neotropical Hexapoda, and Volume IV is the Palaearctic Fauna, which was slightly delayed.  But both are currently in press. 

[7] The Legacy of Calvin Goodrich [23Jan07]

[8] My exact words to Jim and Christopher were, “It’s the fourth quarter of my career.  I won’t take a knee on the ten-yard line.”

[9] Ancylid limpets integrated with the Planorbidae.  OK, fine.

Friday, March 16, 2018

Psst, Buddy! Wanna buy an Apple Snail?

Editor’s Note –This is the sixth (and final) installment in my series on the general topic of freshwater snails in the aquarium hobby.  Previous posts have been “What’s Out There?” [9Oct17], “Loved to Death?” [6Nov17], “Pet Shop Malacology,” [21Dec17], “Snails by Mail” [24Jan18], and “Freshwater Gastropods and Social Media” [14Feb18].  It might help you to read (at least) my previous (February) post on this subject before going on to the essay below.

First let us clarify the situation as pertaining to law.  In addition to their broader body of regulations regarding the movement of gastropods generally, the Feds have a set of explicit restrictions regarding the importation and movement of ampullariids [1].  Quoting the USDA-APHIS verbatim: 
“aquatic snails in the family Ampullaridae (e.g., Pomacea canaliculata, channeled apple snail), with one exception, may not be imported or moved interstate except for research purposes into an APHIS inspected containment facility. One species complex in the family Ampullaridae, Pomacea bridgesii (diffusa) may move interstate without a permit because these snails are not known to be agricultural pests but are primarily algae feeders. An import permit is required for aquatic snails in order to verify species and examine shipments for contaminants that are agricultural pests.” [2] 
Note that it is not illegal to own, buy, sell, trade, breed or propagate invasive apple snails of the maculata/insularum/canaliculata type, conventionally abbreviated IAS.  Naturalized populations of IAS are already widespread in certain regions of the United States.  I, living in South Carolina for example, could easily gather Pomacea maculata from any number of local retention ponds in my area and enjoy them in my home aquarium.  I cannot, however, ship them to my friends in North Carolina, nor carry them in a cooler up I-95.  Nor can my Tarheel buddies come down here and fetch any.

So in last month’s [14Feb18] essay I shared my impressions from 30 days of monitoring the conversation on a Facebook group called, “Snails, Snails, Snails.”  I tallied eight mentions of IAS during that month, including four separate appeals for purchase, and concluded: “Without a doubt, significant pent-up demand exists within the community of aquarium hobbyists for large, invasive apple snails.”

"Last round of Peruvian Apple Snails"

I didn’t mention it at the time, but I am mentioning it now, because I think it is especially significant.  Among the eight mentions of IAS I logged during my 30 days of observation on Snails, Snails, Snails was one offer to sell.  A pet supply store in South Dakota named “Woofs & Waves” posted the photo above, simply captioned, “Last round of Peruvian Apple Snails for the season.”

This post generated 10 comments, plus about 25 associated replies.  Comments included, (1) Cooooool!! and (2) Oh I wish I could get those, and (3) I want one so bad!  He’d do great in my 110! and (4) what does he charge for those?  Where is he located?

The reply to the previous query was, “$9.99, Sioux Falls.”  Then this discussion followed: “I am sure they wold ship if you asked nicely” and “Pretty sure they can’t cuz those are illegal in many places” and “Yeah, South Dakota is pretty lax on wildlife stuff unless you’re poaching.”

I think that independent aquarium stores may be the primary agents for the introduction and spread of invasive apple snails around the USA.  The survey I posted in December [21Dec17] satisfied me that the big-box pet stores don’t sell them, and the desultory survey of major online retailers I published in January [24Jan18], including Amazon and Ebay, didn’t turn up any.  Are Mom-and-Pop independents, which in the patois of social media are called “LPS” (local pet stores), the well from which North American populations of invasive apple snails spring?

Following this hunch, last week I made a field trip across town to the only independent aquarium store in the Charleston Area, a really handsome shop with great stock and a knowledgeable staff called, “Tideline Aquatics.”  And in addition to the usual assortment of mystery snails and nerites and rabbit snails [4], I found offered for sale a small batch of “jumbo gold mystery snails,” maybe six or eight head in the lot, crammed timidly into the corner of an aquarium on the bottom rack, behind the filter.  These are clearly not our benign little friend Pomacea diffusa/bridgesii.  These are invasive apple snails.  Click for larger:

NOT Pomacea diffusa
And more than just any random IAS, my local pet store is apparently stocking golden-form apple snails, of a kind widely introduced throughout Asia and the Pacific Islands.  We don’t host any golden morphs at all in the populations of Pomacea maculata naturalized here in South Carolina.  I’ll bet dollars-to-donuts that the stock of “Jumbo gold mystery snails” for sale a few miles from my house originated from Asia, probably from dealers not unlike the ones surveyed by Ting Hui Ng and her colleagues in 2016 [5].  See figure #14 in the Ng et al. plate I shared with you all back in October [9Oct17].

And here we also reprise a theme I developed in December [21Dec17] – the mysterious origins of aquarium stocks worldwide which, like any other commodity I suppose, it behooves suppliers to protect.  And the plasticity of the names attached to such stocks.  Common use and legal precedent has developed such that “apple snails” are bad and “mystery snails” are good.  So the “jumbo mystery snail” has been born, to mysteriously arrive at an independent aquarium-stock retailer near you.

And so we have now come full circle, which means that it is time to sum up.  I am charmed, genuinely charmed, by the widespread interest and heartfelt love often demonstrated by aquarium hobbyists toward our mutual friends, the freshwater gastropods.  And I think such interests should be encouraged, if for no other reason than they might blossom.  I cannot see how harvest of wildstock freshwater gastropod populations for the aquarium trade could endanger such populations, at any imaginable harvest rates.  I can see, however, a problem with the spread of invasive species.

Here a tiny and obscure freedom, escaping the notice of our founding fathers, is associated both with a tiny societal benefit, and a tiny hazard.  I can’t think of any solution to the tiny hazard, beyond what we’re already doing.  Let’s just leave that freedom alone, shall we?


[1] And I should immediately stipulate that some states have their own regulations more restrictive than the Feds.  Our good buddy Joshua Vlach from the Oregon Department of Agriculture informs me that Oregon has a five-page list of invertebrates that are ALLOWED to cross its state lines, and all others are prohibited [3].   The bottom line is the same for IAS, however.  Go home!

[2] US Department of Agriculture, Animal and Plant Health Inspection Service.  Plant Health / Import into the US / Permits / Regulated Organisms and Soil Permits / Snails Slugs.  [html]

[3] This reminds me of a scene from one of the Peanuts videos, where Violet and Lucy tell Charlie Brown, “There were two lists, Charlie Brown.  There was a list to invite, and a list NOT to invite.  And you were on the WRONG LIST!”

[4] The shells of the “Rabbit Snails” were completely encrusted with calcification.  Absolutely unidentifiable.  The ugliest gastropods I have ever seen in captivity.

[5] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130.  https://doi.org/10.1371/journal.pone.0161130