Red Flags, Water Resources, and Physa natricina

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019d) Red Flags, Water Resources, and Physa natricina.  Pp 153 - 158 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

This past December brought the publication of a brief paper by our colleagues Christopher Rogers and Amy Wethington synonymizing the federally listed “Snake River Physa” (Physa natricina) under the cosmopolitan P. acuta (1). How a local population of an invasive pest came to be protected under the Endangered Species Act is but one blunder in the sad history of fumbles and missteps that has characterized the record of American Malacology in the Snake River Canyon of southern Idaho. Can anything be learned to prevent such embarrassments in the future?

The misadventure began in the early 1980s, when Idaho Power Company proposed the construction of six new hydroelectric projects on the middle Snake River, perhaps to impound the last free-flowing reaches of a 122 mile section already tightly controlled by 11 dams. Environmental groups rose up in opposition (2), and I would freely confess sympathy for their cause. I have a visceral love of rivers and the lotic biota, and hate impoundments because they are ugly, stinking blights, all too rapidly infested with Bud-swilling bass fishermen.

But insults to the public aesthetic will never be as compelling to the permitting agencies as hydropower, irrigation, and jobs, no matter how egregious the choice of beer. Thus it is not a coincidence that within ten years of the announcements by Idaho Power, five species of endangered freshwater gastropods were discovered in the middle Snake River. Pyrgulopsis idahoensis, Valvata utahensis, Taylorconcha serpenticola, Physa natricina, and the undescribed "Banbury Springs lanx" were added to the federal list of endangered and threatened wildlife on December 14, 1992 (3). The Idaho Power hydro projects were shelved.

About "Pyrgulopsis idahoensis" we have written much in recent years (4). Although originally believed endemic to the Snake River, it proved to be a junior synonym of P. robusta, its actual range extending over four states. Far from being endangered, the Snake River population of P. robusta may be the largest single population of freshwater gastropods on earth. Taylorconcha and V. utahensis are also not rare, and are currently being studied for delisting as well (5). And now published is the paper by Rogers & Wethington sinking Physa natricina.

Physa natricina was described in 1988 by Dwight Taylor, a reclusive millionaire whose 44-page obituary will appear in the next Malacologia (6). Although perhaps better qualified as a paleontologist, Taylor often published on the modern terrestrial and freshwater malacofauna of the American West. He is best remembered for his fanciful treatments of the Physidae (7) and the Cuatro Cienegas hydrobiids (8), imagining more higher taxa than valid biological species actually exist to sort into them.

To be fair, Taylor’s 1988 work (9) conformed to the same 19th century standards of practice under which most elements of America's molluscan fauna have been described. He did distinguish his Physa natricina from P. gyrina, a strikingly different animal which is very common in the Snake River. But the brief comparison he offered between his new species and P. integra, the synonym for P. acuta most commonly applied in the upper Midwest, should have raised a red flag. Taylor wrote that the penial sac of P. integra "is more slender, with a kink near its distal end, and is not bent near the middle." Kinks and bends in mollusk anatomy? Was Taylor nuts? (10) One need not be a malacologist - one need only to have eaten an oyster - to realize that anybody who would distinguish the internal anatomy of a gastropod by reference to kinks and bends is simply unqualified for his profession.

Taylor's work was generally characterized by false precision. For example, in his introductory description of the (entire!) subgenus Physa, he stated that the "spawn capsule...is up to about 10 mm long with 20 eggs." But even under controlled conditions here in my laboratory, we commonly record individual Physa egg masses ranging from over 100 embryos to fewer than 1. Meanwhile, about truly important matters Taylor seems to have been careless at best. His statement that the natricina holotype was deposited in the Los Angeles County Museum ("LACM 2256") seems to have been a fabrication. Christopher Rogers was finally able to track down Taylor's P. natricina holotype at the California Academy of Sciences, where it was not deposited until 1999.

And here's another red flag - the hypothesized rarity of the new species. Taylor's original description was based on but two live-collected animals, "despite arduous effort" to obtain more. But species do not exist as individuals - they exist in populations. Any generally-trained biologist might well wonder how a population as sparse as P. natricina seems to have been for over 20 years could remain viable.
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In late 2005 I was pleased to accept an invitation from the Bureau of Reclamation to visit the Minidoka Dam (photo above) on the Snake River east of Rupert, Idaho, for a Physa strategy meeting. Also present were our colleagues Amy Wethington, John Keebaugh, Steve Lysne, and several others. The product of that meeting was a consensus that a sequencing project should be undertaken as soon as the next fresh P. natricina individual might be recovered from the river – a day which never arrived (11). But on the basis of what I was able to learn about that elaborately managed river system, together with my own limited observations of the environment and my general experience with the biology of physids, I offer the following hypothesis (12).

I suggest that the two individual P. acuta from which Taylor described his “Physa natricina” in 1988 may have been flushed into the main Snake River from irrigation ditches. In addition to power generation, many of the Snake River dams serve to divert irrigation water to the surrounding farm land. This is done seasonally, and both the peak diversions and the peak release flows back to the river can be high. I suggest that irrigation waters may sporadically carry elements of the canal-dwelling macrobenthos into the Snake River, including occasional individual Physa acuta.

Science is a self-correcting process. It is gratifying to see two of our own, Rogers and Wethington, designing the research program and publishing the paper that has turned us back from our 20-year blunder. But at such a cost! Literally millions of dollars have been wasted monitoring, managing, and protecting a snail that anyone on six continents could find in the ditch behind his local McDonalds, licking special sauce off the hamburger wrappers. Can we avoid even the first step down such paths in the future?

Yes, if we watch for red flags. And the biggest red flag waving over the Physa natricina blunder was not the vacuous description, the false precision, or the biological implausibility of the phantom snail's very existence. The biggest red flag was that this entire research program was motivated, from its very inception, by water resource politics.

You have heard me preach this sermon before - science and politics do not mix. When the two worldviews collide, compromises must be made, and it's always the science that suffers, in my experience. Malacology was corrupted at least four times by water resource politics in the middle Snake River 20 years ago. And science continues to be corrupted in our professional organizations, from the AAAS to the NAS, on matters ranging from global climate to stem cells. But when we see that red flag fly, we must stop.

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. A pdf reprint can be requested from the author.

(2) Wuerthner, G. (1992) No Home for Snails. Defenders May/June 92: 8 - 14.

(3) US Fish & Wildlife Service (1992). Endangered and threatened wildlife and plants; Determination of endangered or threatened status for five aquatic snails in south central Idaho. 50 CFR Part 17. Federal Register 57(240)59244-57. (December 14, 1992)

(4) I've offered four previous posts on the Snake River Pyrgulopsis: Idaho Springsnail Showdown [28Apr05], Idaho Springsnail Panel Report [23Dec05], When Pigs Fly in Idaho [30Jan06], and FWS finding on the Idaho Springsnail [4Oct06].

(5) More Snake River Gastropods Studied for Delisting [14June07]

(6) Kabat, A. R. & R. I. Johnson (2008) Dwight Willard Taylor (1932-2006): His life and malacological research. Malacologia 50: 175-218.

(7) Wethington, A. R. & C. Lydeard (2007) A molecular phylogeny of Physidae (Gastropoda: Basommatophora) based on mitochondrial DNA sequences. J. Moll. Stud. 73: 241-257.

(8) Hershler, R. (1985) Systematic revision of the Hydrobiidae (Gastropoda: Rissoacea) of the Cuatro Cienegas Basin, Coahuila, Mexico. Malacologia 26: 31 - 123.

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

(10) Yes.

(11) See the Bureau of Reclamation's web site for the "Physa Amendment" to its "2004 Biological Assessment and Opinions for Operations and Maintenance of Reclamation Projects in the Snake River Basin above Brownlee Reservoir." There's also an (8/05) "Implementation Plan for Proposed Snake River Physa Surveys" available toward the bottom of the page.

(12) I don’t remember who first advanced this hypothesis – it was very likely in existence long before my introduction to the matter. And I’m pretty sure I’m not the only one who holds it, but I wouldn't presume to speak for anybody else.

Semisulcospira II: A Second Message from The East

Last month we reviewed the experiments of Urabe (1998, 2000) vividly demonstrating that shell morphology in the East Asian pleurocerid genus Semisulcospira has a substantial non-genetic component. Since the taxonomy of this important group is based almost entirely on its shell, such results suggest that the true number of biological species in the genus Semisulcospira may be much different from the number of nomina conventionally applied.

This month we’ll update that message with a second chapter from Taehwan Lee, Dairmaid O’Foighil, and two colleagues from Pai Chai University in Daejon, South Korea (1). What might the application of modern molecular techniques add to our understanding of evolution in this enigmatic genus from The East?

The range of Semisulcospira libertina extends from Japan onto the Korean Peninsula, where it shares rivers and streams with ten other nominal Semisulcospira species, as judged by their shell morphology. Lee and his colleagues sampled eight of those species from nine sites – libertina (four populations), coreana (two populations), extensa (two populations), and single populations of forticosta, gottschei, multicincta, nodiperda, and tegulata. They sequenced two genes, the mitochondrial 16S and the nuclear 28S ribosomal genes, in most cases just one individual per population but in some cases up to ten or even twenty per population. They built phylogenetic trees using three different methods (maximum parsimony, maximum likelihood, and Baysian) to mollify all constituencies among their reviewers (2), with a couple other genera of Korean pleurocerids added as outgroups (3).

It should come as no surprise, to all of us familiar with Urabe’s work, that the phylogenetic trees obtained by Taehwan, Dairmaid and their colleagues showed a mish-mash of nominal species bearing almost no relationship to the traditional taxonomy based on shell. Only Semisulcospira extensa appeared monophyletic. Populations of the other seven species displayed a genetic structure we have seen much of recently (4) – heterogeneous mixtures with numerically predominant modal clades and the scattered highly-divergent genotypes that (in my post of 7/07) I have called "sports."

Not only were the nominal species polyphyletic, the populations and even the individual snails were polyphyletic. I am ashamed to confess that I was entertained by the author’s discovery of a single S. libertina individual heterozygous at the 28S locus. I should have been compassionate – analysis of this individual snail was apparently a real pain in the can. Taehwan and colleagues had to clone the PCR products amplified from this individual in plasmid vectors and sequence a bunch of recombinant bacterial colonies. The two alleles turned out to differ by 23 nucleotides, leaving the single individual S. libertina that bore them splayed across opposite ends of their 28S maximum likelihood tree. I think I may read phylogenetic systematic research for the same reason I watch NASCAR - the wrecks (5).

Taehwan, Dairmaid and their colleagues reviewed the same list of explanations for this phenomenon that they previously examined in their paper on Laevapex with Andrea Walther in the lead (6) – paralogous mt markers, cryptic species, introgression, and (their choice) retention of ancestral polymorphism through incomplete lineage sorting (7). They concluded with the recommendation that coreana, forticosta, gottschei, multicincta, nodiperda, and tegulata all be synonymized under the single, phenotypically variable biological species Semisulcospira libertina, broadly distributed across East Asia.

In summary, the messages borne to us this month by Taehwan, Dairmaid and their colleagues from The East are that “biologists interested in freshwater cerithiodean molecular phylogenetics approach these taxa as potential morphospecies complexes,” and that in the future “meaningful phylogenetic study of these organisms may well require the use of both mitochondrial and nuclear markers together with population level samples of all nominal taxa within regional drainages.” Message received, guys! And in other news … Ronald Reagan elected President (8).

Notes

1) Lee, T., H. C. Hong, J. J. Kim and D. O’Foighil (2007) Phylogenetic incongruence involving nuclear and mitochondrial markers in Korean populations of the freshwater snail genus Semisulcospira (Cerithioidea: Pleuroceridae). Molec. Phylog. Evol. 43: 386-397.

2) The tiny fringe group who prefers neighbor-joining techniques is not likely to read MP&E, much less referee their manuscripts.

3) It will be recalled from last month’s essay that Semisulcospira is ovoviviparous. As outgroups, Lee et al. selected four species from two strictly oviparous genera of Korean pleurocerids - Hua and Koreoleptoxis.

4) The parallel between these findings and our own (2004) results is striking, although perhaps not of the same magnitude. Dairmaid tells me that the sequence divergence ranged up to 8.9% within his Semisulcospira populations, while we reported up to 14.5% intrapopulation 16S sequence divergence in American Goniobasis. See Dillon & Frankis, Amer. Malac. Bull 19:69-77.

5) With Joe Gibbs running Toyotas in 2008, it may not be too much longer until Sprint Cup fans receive our own “message from The East.”

6) Walther, A., T. Lee, J. B. Burch, and D. Ó Foighil. 2006. E Pluribus Unum: A phylogenetic and phylogeographic reassessment of Laevapex (Pulmonata: Ancylidae), a North American genus of freshwater limpets. Molecular Phylogenetics and Evolution, 40: 501-516.

7) That’s close, but I don’t think exactly right. The likelihood that an ancestral polymorphism will be preserved in a pair of sorted lineages decreases with internodal time, which may be great in populations as old as these. I think such polymorphisms may not the product of incomplete lineage sorting, but rather have evolved endogenously in large, ancient, and isolated populations. And I think independently-evolved genes may converge on the same adaptive peak, or may be collected outside the population cluster in which they evolved by long branch attraction.

8) Dillon, R. T. and G. M. Davis (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia 20: 83-98.

Semisulcospira Research: A Message from The East

'Tis the season for Messages from The East. And in recent years I have taken some inspiration from research conducted on Semisulcospira, a genus of pleurocerid snails widespread throughout Japan, Korea, Taiwan and eastern China. As a potential intermediate host for the lung fluke Paragonimus westermani, Semisulcospira has become one of the better-studied of all the freshwater prosobranchs.

In many of the details of its general biology, life history, and habitat, Semisulcospira reminds me a great deal of our North American Goniobasis or Elimia. Scores of species have been described (30 from Japan alone, according to Davis, note 1), almost entirely on the basis of shell morphology. The most striking difference between Goniobasis and Semisulcospira is that the latter is a brooder - holding eggs in a modified pallial oviduct until hatch. But although ovoviviparity is often associated with parthenogenesis in freshwater gastropods, I'm not aware of any evidence of asexual reproduction in Semisulcospira (2).

Ovoviviparous reproduction does, however, facilitate laboratory rearing studies. And in 1998 and 2000, Misako Urabe (of Nara Womens' University) published a pair of papers describing a set of experiments directly exploring the heritability of shell morphology in Semisulcospira that deserve to be more widely known.

Urabe worked with Semisulcospira reiniana, an extremely variable species co-occurring with (and sometimes indistinguishable from) the more widely distributed S. libertina in the Kamo River of Kyoto. The plate at left (from Davis, see Note 1) shows both S. libertina (figs 1-4) and S. reiniana (figs 5 & 6) from several Japanese populations (scale bar in mm).

In the 1998 work, Urabe (3) used mother/offspring regression to estimate the heritability of the three shell shape parameters of Raup (4): S (the roundness of the generating curve), W (the rate of whorl expansion), and T (the rate of whorl translation). In the wild, snails collected from more rapid currents tended to have larger W and smaller T, that is, larger body whorls and lower spires (5). But lab experiments showed the heritabilities of all three shell shape parameters to be nonsignificant - no different from zero.

In the 2000 work, Urabe (6) reared juveniles to 6.8 mm under standard conditions, marked sibships with waterproof tags, and then divided them into two aquaria - one with a sand substrate and the other with pebbles. After one year, snails were scored by their "rib intensity," a 0/1 coding system for shell sculpture developed by the author. Urabe showed both that mothers with stronger shell ribbing tended to produce higher percentages of ribbed offspring, but that snails grown to maturity in the tank with the sand substrate tended to form ribbed shells more frequently than those grown on pebbles.

Quite a few researchers have directly demonstrated shell phenotypic plasticity using pulmonate snails as models. Amy Krist published a nice experiment showing that crayfish predation can affect aperture shape in Goniobasis livescens a couple years ago (7). But the experiments of Urabe are the best demonstrations of phenotypic plasticity in freshwater prosobranchs of which I am aware.

So to what extent might we expect Urabe's conclusions for Semisulcospira to generalize to the pleurocerids of North America? The evidence is all around us that they do. I've seen populations of Goniobasis catenaria inhabiting Piedmont streams in North Carolina, for example, that intergrade seamlessly from strongly carinate shells to shells almost entirely smooth, apparently in correlation with the substrate (8). And I dedicated my entire post in February 2007 to a phenomenon I called "Goodrichian Taxon Shift," the broadening and thickening of shell morphology demonstrated by populations of North American pleurocerids as rivers widen, deepen, and slow. Which brings us to our "Message from The East."

In recent years, modern research programs have led to substantial taxonomic revisions in the Asian Pleuroceridae. At least 17 of the 30 specific nomina of Semisulcospira described from Japan on the basis of shell character had been synonymized under S. libertina by 1972, according to Davis (9). The clear implication of Urabe's work, that such trends will continue, has recently been borne out, as we shall see. And might the long-benighted pleurocerid fauna of North America also be overdue for a taxonomic revision along similar lines? Again, said the Zen Master, we will see.

Notes

(1) Davis, G. M. 1969. A taxonomic study of some species of Semisulcospira in Japan (Mesogastropoda: Pleuroceridae). Malacologia 7: 211-294.

(2) Males seem to occur in high frequency in all populations.

(3) Urabe, M. 1998. Contribution of genetic and environmental factors to shell shape variation in the lotic snail Semisulcospira reiniana (Prosobranchia: Pleuroceridae) J. Moll. Stud. 64: 329-343.

(4) Raup, D. M. 1966. Geometric analysis of shell coiling: general problems. J. Paleontol. 40: 1178-1190.

(5) To be quite precise - snails active in fast currents at night tended to show the shell shape relationship best. Apparently Semisulcospira populations are nocturnal, much like the Melanoides in my goldfish bowl. Urabe suggested that, since shell growth only occurs when the mantle edge is flush with the aperture, "it is only the environment that a snail experiences when it is active at night-time that affects shell formation." Interesting!

(6) Urabe, M. 2000. Phenotypic modulation by the substratum of shell sculpture in Semisulcospira reiniana (Prrosobranchia: Pleuroceridae). J. Moll. Stud. 66: 53-59.

(7) Krist, A. C. 2002. Crayfish induce a defensive shell shape in a freshwater snail. Invert. Biol. 121: 235-242.

(8) The smooth form is given the subspecific name "dislocata," while the strongly carinate form is G. catenaria s.s.

(9) Davis, G. M. 1972. Geographic variation in Semisulcospira libertina (Mesogastropoda: Pleuroceridae). Proc. Malac. Soc. Lond. 40: 5-32.

Symposium at NABS '08

To the FWGNA group,

Our good friend Bill Clark is co-organizing symposium on sampling low-density populations for the annual meeting of the North American Benthological Society next year in Salt Lake City, May 25 - 30. See Bill's message below. His [PDF] flier is available from the FWGNA site.

Bill and his colleague Leska Fore have been working on the endangered freshwater gastropods of the Snake River. They're hoping to share new methods, discuss unique sampling issues related to benthic species, and perhaps even break into a spontaneous discussion of the future of the ESA. Bill invited any of us who might wish to contribute a paper to this symposium to get in touch with Leska at the contact information below. Looks like a great opportunity!

We'll keep in touch,
Rob


-------------

Subject: Symposium announcement
Date: Mon, 19 Nov 2007 13:32:16 -0500
From: "Clark, William" WilliamClark@idahopower.com
To: "Dillon Jr, Robert T."

Hi Rob:
I wonder if you could send this information for a symposium announcementout to your FWGNA group mailing list? I've attached a one page flyer and the basic information is also presented below in the email.

Thank you very much,
Bill Clark (and Leska Fore)

William H. Clark,
Macroinvertebrate Biologist
Idaho Power Company
P.O. Box 70
Boise, Idaho 83707 USA
tel: 208-388-2689
FAX: 208-388-6902
email:WilliamClark@idahopower.com

______________________________

Quantitative Methods for Evaluating the Status of Threatened Species
Organizers: Leska S. Fore, Statistical Design, Inc. & William H. Clark,Idaho Power Co.
Contact: Leska Foreleska@seanet.com
206 632-4635

Many of the benthic freshwater species identified to be at risk for extinction, e.g., mussels, clams, and snails, may be rare, unevenly distributed, or hard to detect. The focus of this session is on the quantitative methods used to assess population size, condition, orchange, such as mark-recapture, multi-stage survey sampling, and adaptive sampling. The goal of this special session is to bring together practitioners working with at risk populations to compare the limitations and advantages of various methods for different geographic settings and different types of organisms. Results from these studies can have enormous economic impact; for example, when power generation is limited at hydroelectric facilities to protect a threatened species. This session is not limited to any particular species group or any particular method of population assessment. General methods papers related to sampling are also welcome. Of greatest interest are studies in which the scientific results are embedded in the decision process forspecies conservation and protection.--

Leska S. Fore
Statistical Design
136 NW 40th St.
Seattle, WA 98107
(206) 632-4635 phone
(206) 632-3752 fax
www.seanet.com/~leska

Ducks, Snails, and Worms - When Invasive Species Conspire!

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019d)  Ducks, snails, and worms - When invasive species conspire!  Pp 11 - 14 in The Freshwater Gastropods of North America Volume 4, essays on Ecology and Biogeography.  FWGNA Press, Charleston.

Freshwater snails have suffered a spate of bad press in the upper Midwest recently. Late last week our friend Henry Fieldseth sent us an article from the Minneapolis Star Tribune (6Nov07, pasted below) attributing the death of thousands of waterfowl in a local lake to infections by trematode worms, with the "banded mystery snail" (Viviparus georgianus) indicted as a co-conspirator. This is not the first mass murder rap to be pinned on a digenean trematode or an invasive gastropod henchman, nor will it be the last, I fear.

Massive late-summer mortalities of waterfowl attributable to trematodiasis have been reported at least since the 1960s, when thousands of ducks were apparently killed by mixed infections of the digeneans Cyathocotyle bushiensis and Sphaeridiotrema globulus in the St. Lawrence River south of Quebec. Hoeve & Scott (1) linked these deaths to ingestion by the ducks of the invasive European gastropod Bithynia tentaculata. In 1997, tens of thousands of coots were killed in Wisconsin's Shawano Lake by a third digenean worm, the European Leyogonimus polyoon, again carried by Bithynia (2). And since 2002, all three worms have been implicated in massive waterfowl mortalities around Lake Onalaska, a backwater of the upper Mississippi River near La Crosse (3). All three of these digenean trematodes, the introduced Leyogonimus as well as the natives.
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Cyathocotyle and Sphaeridiotrema, display Type III life cycles – entering their ultimate (vertebrate) host by ingestion of an infected meal (4). The vertebrate host sheds eggs through its feces, which hatch into ciliated miricidia and penetrate the first intermediate host, a freshwater gastropod. (The photo of Bithynia tentaculata at left was taken by Lars Peters.) The miricidium develops numerous sack-like rediae in its first intermediate host, each of which gives rise to many cercariae. Then the cercariae swim out of the snail to find a second intermediate host, which may be selected from among a wide variety of aquatic animals – a second snail or an aquatic insect, for example. (Typically substantial specificity is demonstrated for the first intermediate host, but not for the second.) The definitive vertebrate host (a duck or coot in this case) becomes infected with mature worms when it ingests the second intermediate host.

Trematodes do not typically kill their definitive hosts. The massive mortalities we have seen scattered through diverse waterfowl populations in the upper Midwest are most likely attributable to unusually high rates of snail ingestion as well as to double or exotic infections. So since the ducks (with their digenean parasites) disperse readily on continent-level scales, federal and state agencies have signaled their intent to focus their efforts to control the trematodiasis by controlling the snails (5).

Thus last week's discovery of the massive waterfowl mortality attributable to Cyathocotyle and Sphaeridiotrema in Minnesota's Lake Winnibigoshish is especially bad news. For if the initial reports hold up, here the first intermediate host of the worm is not Bithynia, but rather Viviparus georgianus (6). Viviparus georgianus is a native of the American southeast, and is much more widely distributed throughout the United States than Bithynia. And if the problem trematodes can infect Viviparus, they would also seem likely to be able to exploit Bellamya (Cipangopaludina) and Campeloma, and in so doing expand their potential ranges nationwide.

I am often asked about the potentially negative effects of artificially-introduced freshwater gastropod populations. My usual response has been that such effects are difficult to establish. Very few studies have ever demonstrated community or ecosystem effects attributable to exotic freshwater gastropods – they seem to invade environments that are already disturbed and compete rarely (if ever) with native populations.

But here splashed across our morning newspapers we read that "carcasses dropped by eagles hung in the trees on the island, and feathers littered the shore" (LaCrosse Tribune 28Oct07, link removed). This is a dramatic example of unfortunate environmental consequences directly attributable to the spread of exotic freshwater gastropods. And at this point I don't think that snail control will solve the problem. And I really wish I could think of any other alternative.

We'll keep in touch,
Rob


Notes

(1) Hoeve, J. and M. E. Scott (1988) Ecological studies on Cyathocotyle bushiensis (Digenea) and Sphaeridiotrema globulus (Digenea), possible pathogens of dabbling ducks in southern Quebec. J. Wild. Diseases 24: 407 - 421.

(2) Exotic parasite causes large scale mortality in American coots. USGS-NWHC Fact Sheet 6/2001. [PDF]

(3) Exotic parasite of American coot discovered in exotic snail in Lake Onalaska. USGS-NWHC Bulletin 07-01. [PDF]

(4) See my Chapter 6 of Dillon (2000) for a more complete review of trematode life cycles, from the standpoint of the gastropod. Although most of that chapter (perhaps unsurprisingly) focuses on Type I Fasciola and Type II Schistosoma, there is a bit about Type III Echinostoma as well.

(5) Finding the exotic faucet snail (Bithynia tentaculata): Investigation of waterbird die-offs on the upper Mississippi River National Wildlife and Fish Refuge. USGS-NWHC report 2007-1065. [PDF]

(6) Scaup and Coot die-off at Lake Winnibigoshish. Minnesota DNR:
http://www.dnr.state.mn.us/hunting/waterfowl/scaup.html



------[Minneapolis Star Tribune 6Nov07]---------

Nov. 6: Parasite has killed thousands of scaup
The deadly organism has infected snails at Lake Winnibigoshish and has been picked up by the ducks, who dive below water to feed. The DNR is concerned the parasite might spread to other lakes.
By Doug Smith, Star Tribune
Last update: November 08, 2007 – 4:49 PM

A parasite has killed thousands of ducks on Lake Winnibigoshish in northern Minnesota, and could kill many more before the fall migration is over."We picked up 1,000 dead scaup [also known as bluebills] on Saturday," said Steve Cordts, Minnesota Department of Natural Resources waterfowl specialist.

He saw many other scaup still alive but unable to fly, or to fly far. "You could boat right up to them," Cordts said. Perhaps 3,000 ducks, mostly scaup, and some coots have died in the past week. "I'm sure there's more dead birds," Cordts said Tuesday.The ducks apparently are dying from trematodes, a tiny 1-millimeter intestinal parasite or fluke that has infected snails in the lake. Scaup -- a duck that dives below water to feed -- eat the snails, then are infected. "They essentially bleed to death," Cordts said.

The parasite was confirmed in scaup and coots sent to the National Wildlife Health Center in Madison, Wis. Similar die-offs caused by trematodes have occurred spring and fall since 2002 on the Mississippi River near La Crosse, Wis., killing about 40,000 ducks and coots since then. Die-offs again are occurring there this fall.

Cordts said he's not sure how the trematodes made it to Winnie. They apparently have infected a snail called the banded mystery snail, which was first found on Winnie about eight years ago. They are infecting the faucet snail on the Mississippi.

Officials aren't sure how many ducks might eventually die on Winnie, or what impact, if any, it will have on the scaup population. But Cordts is concerned that the snails and parasites might spread to other Minnesota waters. Other duck species also could eat the snails and become infected, he said.

There is concern because the continental scaup population has been declining since 1984 and hit an all-time low last year at about 3 million. Hunters annually kill about 300,000. Minnesota hunters killed about 20,000 last year. Lake Winnibigoshish is a major scaup resting area during migration. "We could have 20,000 scaup show up on Winnie right now," Cordts said. "If that happens, they'd pretty much all be at risk."

Cordts plans to check the lake again today, but he won't collect any more dead ducks. Instead, carcasses will be left to decompose or be eaten by scavengers. The parasite apparently is not a threat to other species, including humans, but Cordts said hunters shouldn't eat sick waterfowl.

Doug Smith • dsmith@startribune.com
© 2007 Star Tribune. All rights reserved.

The Classification of the Physidae

Editor's Note.  This essay was subsequently published as: Dillon, R.T., Jr. (2019b) The classification of the Physidae.  Pp 189-192 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston.

I'm pleased to report that Amy Wethington's excellent 2004 dissertation has, at long last, found its way to publication (1). "A molecular phylogeny of Physidae (Gastropoda: Basommatophora) based on mitochondrial DNA sequences" is now available as a PDF download from the link below. Our congratulations go to Amy and to her advisor, Chuck Lydeard, for a job well done!

Amy sequenced fragments from both the CO1 and 16S mitochondrial genes (summing to 1,200 bp) from a sample of 65 individual physids, representing 28 nominal taxa (2). The results of her phylogenetic analyses dovetail nicely with her anatomical observations, as well as with the growing body of experimental evidence demonstrating little reproductive isolation among many physid populations formerly considered specifically distinct. Amy and Chuck propose a return to the simple two-genus classification system favored by Thiele and Zilch - Physa and Aplexa - the former with about ten species and the latter with but one.

Although their sample size within any single physid population was kept small by the exigencies of scale, Amy and Chuck demonstrate in their analysis the appreciation for interpopulation variation that characterizes all good evolutionary science. Amy has published at least 14 papers on the genetics, ecology, behavior, and reproductive biology of Physa over the last 15 years. She first familiarized herself thoroughly with her organism, then sequenced its genes and cranked out her phylogenetic trees. It shows.

Amy is currently an assistant professor at Chowan University in Murfreesboro, North Carolina (3). We'll look forward to many additional contributions from her in the future!

And keep in touch,
Rob


Notes

(1) Wethington, A.R., & C. Lydeard (2007) Journal of Molluscan Studies 73: 241 - 257. [PDF]

(2) Amy's sample of taxa was primarily North American, but did include fontinalis from The Netherlands, marmorata from Guadeloupe, and acuta from several spots around the world.

(3) Email Amy at wethia@chowan.edu

Cave Snail Adventure

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019c) Cave Snail Adventure.  Pp 217 - 222 in The Freshwater Gastropods of North America Volume 3, Essays on the Prosobranchs.  FWGNA Press, Charleston.

Last month I enjoyed one of the grander adventures of my professional career, an expedition in search of the (nearly-endemic) cave snail of southwest Virginia, Holsingeria unthanksensis (1). The essay that follows is a travelogue of my experiences and observations. In addition, as an innocent-abroad newly introduced to cave biology, I picked up a couple unexpected insights of a more general ecological nature on the expedition, which I humbly offer here for your interest.

Unthanks Cave, with about 7.3 miles of mapped passages, was purchased by The Nature Conservancy several years ago and has recently been deeded over to the Commonwealth of Virginia. The leader of our expedition was Wil Orndorff, coordinator of karst protection for the Virginia Department of Conservation & Recreation (DCR). There were two other DCR personnel on the trip with us, Carol Zokaites and Bill Dingus, as well as Brian Watson and Melanie Stine from the Virginia Department of Game & Inland Fisheries and myself. Melanie took the photo (below) of me, Brian, Wil, Bill, and Carol.
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The cave is roughly Y-shaped (about as rough as the letter Y could possibly be) with a base of perhaps 100 meters, a right prong extending perhaps a mile to pools wherein the Holsingeria dwell, and a left prong extending many miles, intersecting along its course a small underground stream. No Holsingeria were previously known from this left prong.

The six of us entered the cave through a locked gate, descended a rocky slide, and headed down the right prong about 10:00 one steamy mid-July morning, half climbing over boulders and half crawling in the mud. It was real exciting. Some of the wetter rooms featured lovely stalactites, aprons, flowstones, and all manner of classic cave formations. But most of the rooms were dry(ish), and hence the walls and ceilings were bare, although often towering to great height or falling to inky darkness.

Closer to the mouth of the cave we saw a couple species of very pretty salamanders and cave crickets with long, spidery legs. As our journey progressed we saw blind isopods and amphipods, planarians, and beetles. None of these populations was large - all seemed to be sparse inhabitants of tiny habitat patches in a vast expanse of black nothingness.

Around noon we arrived at the end of the right prong of the cave, and a series of small shallow pools of crystal-clear water. I don't think there were more than 10-12 such pools, some just a few feet long, generally no more than a few inches deep. And on the small cobbles in these pools, if one got on one's knees and made a careful inspection, very occasionally one could spy tiny white snails no more than perhaps 4 mm in maximum dimension - Holsingeria unthanksensis. The photo at left was taken by Wil.

My first impression was that, surely, this can't be the entire habitat, nor all the snails. My general experience has led me to expect hydrobiid populations, especially in springs, to look like grains of sand on the beach. But I'd guess that the six of us spent 15 - 20 minutes on our knees just observing, and I don't think we saw more than 20 - 30 animals in total. Wil collected three.

I was also impressed, oddly enough, by the shells of dead land snails scattered about this particular little region of the cave. I do not know how far we were under the surface at this point, but I don't think we were very deep. After our initial descent through the cave mouth our journey was more-or-less horizontal, and occasionally the ceilings were quite high, 30 meters or more. I should guess that the energy input to this system comes from fine organic debris raining from the surface. And I think land snails quite often, burrowing deeply into the rocky hillside above, slip and plummet to their deaths on the cave floor below.

Wil had visited this particular spot on at least two previous occasions, and his strongest impression was that the water levels were strikingly low. Southwest Virginia had been suffering a drought for many weeks, with the Powell River at about 10% of its historic daily flow. Wil was also surprised not to find any of the second species of hydrobiid documented from this site, Fontigens nickliniana. Bob Hershler's original description of the environment mentioned that Holsingeria was found together with Fontigens, a much more widespread taxon, locally very common in above-ground springs. Wil had also noticed the Fontigens on his earlier trips. But on this day, no Fontigens were in evidence.

These observations led me to the first of what I should characterize as an "unexpected revelation." Yes of course, cave environments are generally more stable than surface environments. But that doesn't mean that caves don't change. There was plenty of evidence in the cave of water levels much higher than those we observed - some levels lasting long enough to form "rimstone" around the pools, and some levels simply evidenced by damp marks. It can't be too many years before any such tiny population of aquatic snails must go extinct, right?

We next decided to walk back almost to the entrance of the cave and explore the left prong, our objective being the small river about a mile further down this second passage, from which no aquatic gastropods have ever been observed, by John Holsinger (2) or by anybody else. It was Wil's hypothesis that snails do not inhabit this river because the environment is too flashy - perhaps too variable in temperature or too closely in contact with the surface. But about 10-15 minutes of searching by four of us did uncover one (individual!) Holsingeria at the left prong river. A range extension!

In fact, Holsingeria unthanksensisis not endemic to Unthanks Cave. The species has been collected in at least four other caves scattered about southwest Virginia, with an enigmatic population (3) documented from Skyline Caverns as well, perhaps 300 miles north down the Shenandoah Valley. These caves all lie in Ordovician Limestone that reaches the surface in ribbons and patches through the ridge and valley province that extends from Tennessee to Pennsylvania.

So the second "unexpected revelation" I took away from my big adventure to Unthanks Cave was that what we were doing, essentially, was dropping a tiny bucket dredge on the bottom of splattery ocean many hundreds of miles long. My colleagues in the marine biology community understand that, if they find 30 snails in dredge #1 and zero snails in dredges #2 - 10, it doesn't mean that the snails were endemic to site #1, and that their total population size was 30. Rather, they interpret such data as the consequence of a patchy distribution, the degree of apparent patchiness being a function of sample volume (4). And the snails may not be rare, nor their extinction imminent.

Our stalwart party emerged from Unthanks Cave around 4:30 that afternoon, blinking in the light, baking in the heat, exhausted, muddy, and sore. What a great day! My special thanks go to Wil Orndorf (VaDCR) and Brian Watson (VaDGIF) for directing and producing this, our brief peek through a tiny window, into another world.

Keep in touch!
Rob


Notes

(1) Hershler, R. H. (1989) Holsingeria unthanksensis, a new genus and species of aquatic cavesnail from eastern North America. Malac. Rev. 21: 93-100.

(2) I should like to meet Dr. John R. Holsinger, the cave biologist who first brought Bob Hershler's attention to the little snails that bear his name. Holsinger, who has a tremendous reputation in the local caving community, was the primary author of the cave map Wil used to guide our expedition.

(3) The taxonomic status of the Skyline Caverns snail is unsettled at this point. Hershler considers it "a probable congener" of H. unthanksensis.

(4) I'm not sure that ecologists are as conscious of sampling as we once were. My favorite reference on dispersion patterns and spatial distributions is an older one - Chapter 4 of R. W. Poole's (1974) Introduction to Quantitative Ecology (McGraw-Hill).