Crisis At Lake Waccamaw?

Editor's Note. This essay was subsequently published as: Dillon, R.T., Jr. (2019d) Crisis at Lake Waccamaw?  Pp 193 - 199 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

Deep in the cypress swamps shrouding the remote southeast corner of North Carolina lie the mysterious waters of Lake Waccamaw. At roughly 9,000 acres and 4 miles across, Lake Waccamaw is the largest of the “Carolina Bays,” pothole-shaped depressions of unknown origin in an Atlantic Coastal Plain otherwise featureless in its topography. But beyond its unusual size, Lake Waccamaw is distinguished by its exceptional water quality. Groundwater filtering up through layers of sand and Plio-Pleistocene shell arrives in the big lake clear and near-neutral in pH, much in contrast to the acidic and tannin-stained waters prevailing elsewhere throughout the region (1). Although quite young geologically, one might not be surprised to find endemic species (2).

I first visited Lake Waccamaw in 1978, driving south from Philadelphia with Dr. George Davis, my Ph.D. advisor. Our mission was to sample the lake's endemic population of Elliptio waccamawensis for an NSF-funded project on unionid evolution (3). I vividly remember the abundance of the mussels that greeted us that spring morning we waded into the clear shallows together. George and I were able to sample 30 E. waccamawensis in a matter of minutes, with at least four or five other unionid species also moderately common (4). I did not focus on the gastropods that day, but do recall the hydrobiids like pepper on the maidencane.

The entire molluscan fauna of Lake Waccamaw was thoroughly surveyed shortly thereafter by Hugh Porter, working for the North Carolina Wildlife Resources Commission (5). Although I have not seen Porter’s (1985) report, several years ago I had the opportunity of reviewing the extensive collections he deposited in the NC State Museum. Sampling randomly on bottoms of four depth classes with a diver-operated suction dredge, Porter documented strikingly high abundances of the notable Lioplax subcarinata and Gillia altilis, plus the (more mundane) Campeloma decisum, Amnicola limosa, Lyogyrus granum, and the usual pulmonates (6). Especially common in Porter's samples was the little hydrobiid he called “Cincinnatia sp,” but which today is perhaps better referred to the genus Floridobia (7). There has long been speculation that this population may constitute yet another species endemic to Lake Waccamaw (8).

Has the entire diverse and endemic molluscan fauna of Lake Waccamaw now vanished before our eyes? In late May I drove up to the lake from Charleston for a long day of kayaking and puttering about in the shallows. I visited the southern (more exposed) shore near the dam and the northeastern (more protected) shore near the mouth of Big Creek, spending several hours in each area. I examined all wadeable environments and habitats, netted through the entire range of substrates, and found essentially nothing. I observed no more than a couple living unionids all day, and perhaps a handful of empty valves. No Gillia, no Lioplax, not even any Helisoma, and just a few living hydrobiids in the sediments around the macrophytes. I spotted several small Campeloma crawling in the sand, and some Physa bravely clinging to the debris.

I understand that many of the mollusk populations of Lake Waccamaw do not reach their maximum abundance in easily-accessible shallows (9). So the most alarming hours of my visit in late May were spent inspecting the beach drift, which (one might hope) would afford a more random sample of the lake fauna as a whole. In more than an hour of beachcombing on both shores I recovered only perhaps 20-30 tiny Floridobia shells the from grass wrack, 5-10 Amnicola, and a few small Campeloma, period.

Upon my return to Charleston I swapped an email or two with Dr. Diane Lauritsen (10), who has some thirty years of experience at Lake Waccamaw, and spoke with her on the telephone at length. Diane reported that the lake has suffered filamentous algal blooms recently, with an apparently correlated reduction in benthic macrofauna. Diane sent me the photo below.

She mentioned that the Corbicula population (11), while never terribly abundant, suffered a "massive die-off probably four years ago." Diane suggested that Corbicula might be a "canary in the coal mine," telegraphing a warning of hypoxia. I was stunned. I had not seen any evidence whatsoever of Corbicula during my entire day on Lake Waccamaw, not one single bleached valve. In what sort of nightmarish environment might the nasty, invasive Chinese clam become a "canary?"

And what can be done? At the risk of sounding like the scientist I am, we need a formal study. Everything I have reported in the preceding seven paragraphs is anecdotal, and cannot constitute a basis for doing much else. Thank heaven the NCWRC had the foresight to commission Hugh Porter’s study in the late 1970s. The first order of business must be to see a study of that caliber repeated.

So in the end, this essay is an appeal to North Carolina natural resource agencies, the regional offices of conservation-minded NGOs, and Waccamaw-area citizens’ groups to renew our mutual interest in the biological treasure that is Lake Waccamaw. I fear this marvelous resource has been neglected in recent years. But I hope I am wrong.


Notes

(1) More about the geology and water balance of Lake Waccamaw here: J. C. Stager & L. B. Cahoon (1987) The age and trophic history of Lake Waccamaw, North Carolina. J. Elisha Mitchell Sci. Soc. 103: 1-13 [html]. S.R. Riggs, D.V. Ames, D.R. Brant, and E.D. Sager (2000). The Waccamaw Drainage System: Geology and Dynamics of a Coastal Wetland, Southeastern North Carolina. NC Division of Water Resources. [pdf or html]

(2) The nominally-endemic fauna of Lake Waccamaw includes three fishes described in 1946 and a caddis fly described by our colleague Jim Glover in 2004, as well as the unionids Elliptio waccamawensis (Lea 1863) and Lampsilis fullerkati Johnson 1984. The specific status of the two mussels has been called into question, however, in a recent MS thesis: Sommer, K. (2007) Genetic identification and phylogenetics of Lake Waccamaw endemic freshwater mussel species. MS Thesis, UNC Wilmington. [html - pdf]

(3) Davis, G. M., W. H. Heard, S. L. H. Fuller & C. Hesterman (1981) Molecular genetics and speciation in Elliptio and its relationship to other taxa of North American Unionidae. Biol. J. Linn. Soc. 15: 131-150.

(4) Porter listed 11 unionid species, but Bogan puts the number as high as 17: Bogan, A.E. 2002. Workbook and key to the freshwater bivalves of North Carolina. North Carolina Museum of Natural Sciences, Raleigh. 101 pp.

(5) Porter, H. J. 1985. Rare and Endangered Fauna of Lake Waccamaw, North Carolina Watershed System: Molluscan Census and Ecological Interrelationships. North Carolina Wildlife Resources Commission, Raleigh. 187 pp. I understand that this work included quite a few original photographs, and is consequently rather hard to get hold of. The methods and a subset of the unionid results did see publication, however, as: Horn, K. J & H. J. Porter (1981) Correlations of shell shape of Elliptio waccamawensis, Leptodea ochracea and Lampsilis sp. with environmental factors in Lake Waccamaw, Columbus County, North Carolina. The Bulletin of the American Malacological Union for 1981: 1 - 4. Porter, H. J. & K. J. Horn (1983) Habitat distribution of sympatric populations of selected lampsiline species in the Waccamaw drainage of eastern North and South Carolina. Amer. Malac. Bull 1:61 - 68.

(6) Porter counted 10 gastropod species in Lake Waccamaw, but I have 12 confirmed in the FWGNA database: Six pulmonates (Physa pomilia, Helisoma trivolvis, H. anceps, Menetus dilatatus, Lymnaea columella, Laevapex fuscus), the two viviparids (Campeloma and Lioplax) and the four hydrobiids (Gillia, Amnicola, Lyogyrus and Floridobia).

(7) Thompson, F. G. & R. Hershler (2002) Two genera of North American freshwater snails: Marstonia Baker, 1926, resurrected to generic status, and Floridobia, new genus (Prosobranchia: Hydrobiidae: Nymphophilinae). The Veliger 45: 269 - 271.

(8) Porter suggested that the Lake Waccamaw fauna might include two endemic hydrobiids, which he called "Cincinnatia species 1" and "Amnicola species 1." He may be right about the former - populations of the little snail called variously Cincinnatia or Floridobia are quite unusual in southern Atlantic drainages. But Porter's samples of "Amnicola species 1" in the NC State Museum looked like unremarkable mixtures of Amnicola limosa and Lyogyrus to me.

(9) The lake bottom is rather heterogeneous, including some regions of (rather malacologically uninteresting) mud and peat, and other sandier regions that can support surprisingly high abundances of bivalves and gastropods. Benthic algae seem to extend to unusual depths in Lake Waccamaw. Or at least they did in the past.

(10) You might recognize Diane’s name from several excellent works Corbicula feeding, for example: Lauritsen, D. (1986) Filter-feeding in Corbicula fluminea and its effects on seston removal. J. N. Am. Benthol. Soc. 5: 165-172.

(11) The Waccamaw Corbicula population has figured in several research projects: Stiven, A.E. & G. A. Arnold (1995) Phenotypic differentiation among four North Carolina populations of the exotic mussel Corbicula fluminea. J. Elisha Mitchell Sci. Soc. 111:103-115. Cahoon, L. B. & D. A. Owen (1996) Can suspension feeding by bivalves regulate phytoplankton biomass in Lake Waccamaw, North Carolina? Hydrobiologia 325:193-200.

Western Workshop 2010

Our good friend Bill Clark has invited us all to a freshwater mollusk identification workshop out in Idaho this October, with bivalves and gastropods from throughout western North America on the lab benches. Download his flyer from the FWGNA site for all the details:

Idaho Workshop 2010 [PDF]

Bill's contact information is below. He tells me that his organizing committee has not set a firm registration deadline, but that they will need to have a good estimate of attendance sometime in September for planning purposes. "First come, first served."


-----Original Message-----
From: Bill Clark [mailto:clarkfam1@mindspring.com]
Sent: Thursday, June 24, 2010 2:28 PM
To: Dillon, Robert T
Cc: Steven J. Lysne; Bill Bosworth; Richard A. Salisbury; Robert Hershler; Jack Burch
Subject: Mollusk Workshop - Idaho
Hi Rob,
I'm attaching a flyer announcing our October 28-30 Mollusk Workshop here in Idaho. I'd appreciate it very much if you could please send this out to your NA Gastropod Group mailing lists.
Thank you so much,
Bill Clark

-----------------------
William H. Clark, Director
Orma J. Smith Museum of Natural History
The College of Idaho
Caldwell, ID 83605 USA
208-459-5507, 208-375-8605
bclark@collegeofidaho.edu
clarkfam1@mindspring.com
http://www.collegeofidaho.edu/campus/community/museum
.

Unlocking the Keystone State

Editor’s Note. This essay was subsequently published as: Dillon, R.T., Jr. (2019d) Unlocking the Keystone State.  Pp 219 - 222 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

The Commonwealth of Pennsylvania spans every aquatic habitat that one might characterize as "northeastern," across the Delaware, Chesapeake, Ohio, and Great Lakes drainages, both the glaciated and the not. The Keystone State also includes two large and important cities, Philadelphia and Pittsburgh, each with a fine natural history museum. The diverse waters of Pennsylvania have been sporadically but professionally surveyed for almost 200 years.

In 2008 our colleagues Ryan Evans and Sally Ray published a thorough review of museum holdings in Pennsylvania freshwater gastropods, not just at the Academy of Natural Sciences in Philadelphia and the Carnegie Museum in Pittsburgh, but through the electronic databases of 9 other institutions as well (1). Perhaps not surprisingly, they found records of an impressive 63 species.

Now in the most recent American Malacological Bulletin, Evans and Ray have published the results of the first modern survey of The Keystone State, "Distribution and environmental influences of freshwater gastropods from lotic systems and springs in Pennsylvania, with conservation recommendations (2)." The authors sampled 398 sites selected to cover the range of USGS "hydrologic units" encompassed by the state (3), measuring water chemistry variables and extracting a variety of landscape variables using GIS techniques. And the number of species they have confirmed by field collection was ... 37.


Has there been some catastrophic extinction? Almost as alarming as the complete absence of 26 specific nomina from Evans and Ray's field survey were the details of their Table 1, which reported 7 of the 37 species actually recovered at but single sites, of the 398. Has a meteor smashed into the Keystone State in the last 200 years, leaving no trace but the bleached shells of 52% of the freshwater gastropod fauna?

Of course not. We must not overlook the fact that Evans and Ray focused their fieldwork almost entirely upon wadeable streams and springs, excluding marshes, ponds and lakes, and gave very little coverage to large rivers. And natural lakes and ponds are not common in Pennsylvania in any case; the Erie/Ontario drift and lake plains ecoregion just barely nips the northwest corner of the state.

So downloadable from Note (4) below is a spreadsheet listing the 63 freshwater gastropod species that Evans and Ray documented from Pennsylvania in 2008, ranked by the number of sites at which they were recovered by the field survey of 2010. The 26 missing species are listed at the bottom, with number of sites = 0.

Subtracted in Column D are 13 specific nomina with taxonomic problems, leaving 50 species I wouldn't question. Then in Column E I have listed 17 species as "Northern Lentic" - primarily characteristic of lakes, ponds, and marshes, becoming much more common north of Pennsylvania. This subset includes 11 of the 26 species missing from Evans and Ray's 2010 field survey, and 3 of the species collected at but single sites.

Column F subtracts five species for "other sampling problems" as noted by Evans and Ray themselves, and Column G subtracts six introduced species. The bottom line seems to suggest that just two Pennsylvania freshwater gastropod species may warrant conservation concern if viewed from a larger perspective - Lioplax subcarinata (5) and Gillia altilis.

Think Continentally, Act Regionally. It is clear that the conservation implications of the data collected by Evans and Ray can only be interpreted in the context of the larger freshwater gastropod faunas north, south, and west. But it is equally clear that the field survey that brought us these marvelous data was funded by the Pennsylvania Department of Conservation and Natural Resources, an organization with no mandate outside the state lines. Evans and Ray and the PaDCNR are to be highly commended for this effort. If the FWGNA project can only be built one stone at a time, they have contributed a key.


Notes
(1) Evans, R. R. & S. J. Ray (2008) Checklist of the freshwater snails (Mollusca: Gastropoda) of Pennsylvania, USA. Journal of the Pennsylvania Academy of Science 82: 92-97. [PDF]

(2) Evans, R. R. & S. J. Ray (2010) Distribution and environmental influences of freshwater gastropods from lotic systems and springs in Pennsylvania, USA, with conservation recommendations. Am. Malac. Bull. 28: 135-150. [PDF]

(3) The EPA "Surf your Watershed" website lists 58 eight-digit HUCs for Pennsylvania: Surf Pennsylvania

(4) Download an excel spreadsheet analyzing Evans and Ray's (2008, 2010) freshwater gastropods of Pennsylvania. [FW-gastropods-PA.xls]

(5) Evans and Ray "did not feel that adequate survey data were available to give a conservation status recommendation for Lioplax subcarinata."

Influential Publications in Freshwater Gastropod Conservation

Back on April 22 I forwarded the following email from our good friend Bob Hershler to the FWGNA group:

We are preparing a paper on “Molluscan conservation over the past 50 years” for the upcoming UNITAS conference and toward that end we are asking the malacological community to help us identify the most important/influential publications on the subject between 1960-2010. If you have the time and interest, please send us a short list of no more than 5 publications that you consider to be in this category. Thanks very much in advance!

Bob Hershler (hershlerr@si.edu)
Rob Cowie (cowie@hawaii.edu)

Bob indicated that he will be accepting nominations through the first week of May. So there's still a bit of time to send him your suggestions, if you hurry.

I myself struggled with this assignment. Freshwater gastropod faunas are fundamentally regional, as are we researchers who study them, as are the conservation communities that rise to their defense, as are state agencies, as indeed even is the US Fish and Wildlife Service. There is no reason to expect that an inventory of gastropod species facing extinction from impoundments in Alabama, for example, should have any influence on livestock degradation of springs in New Mexico, no matter how compelling.

So I decided to subdivide my nominations by region. As of 5/2010, the US endangered species list includes 9 freshwater gastropods from the Mobile Basin of Alabama, 5 from the arid southwest, 5 from the Snake River, 2 from Tennessee, and 1 from Missouri. My initial idea was to gauge the "influence" of candidate publications by examining the literature cited sections of the entries in the Federal Register in which these 22 species were proposed, perhaps according more importance to the earlier references than to the later ones.

But a dichotomy immediately presented itself. Here in the East, the publications that seem to have influenced gastropod conservation all advance the argument, "Species X was common, and is now rare." So the proposals in the Federal Register for Alabama and Tennessee species cite 19th-century works of taxonomy, 20th-century alarms of a general nature, and unpublished status reports documenting the specific conservation situation. But in the West, species arrive rare. The Federal Register cites 20th-century works of taxonomy leading directly to unpublished status reports, skipping the general calls to alarm.

Ultimately I decided not to offer any recommendations for The West. I have very little experience in western regions, and (from the outside) was unable to identify any publications of even regional influence. Within the East I have divided my nominees into the Tennessee region, the Alabama region, and a special category from the Northeast.

First Place, Tennessee Region
Stansbery, D. H. (1970) Eastern Freshwater Mollusks (I) The Mississippi and St. Lawrence River Systems. Malacologia 10: 9-22.

This was the most lengthy contribution to the "Symposium on Rare and Endangered Mollusks of North America" organized by Arthur Clarke for the 1968 AMU meeting in Corpus Christi. Clarke edited the proceedings of the entire symposium for publication as a unit in the 1970 Malacologia 10: 3 - 56. That symposium featured contributions by 14 prominent malacologists of the day (1), and might justifiably be cited as a single work.

Dave Stansbery was primarily a unionid worker, but directed some attention in his paper to the status of pleurocerid populations in the eastern and central regions of North America. He specifically highlighted Io fluvialis ("A few relic populations remain") and Athearnia ("Eurycaelon - a few populations of at least one species yet survive.") In subsequent papers (2) Stansbery went on to document the elimination of Io from the North Fork Holston River, its type locality.

As the symbol of the American Malacological Society, Io fluvialis is literally "iconic." The alarm bell rung by Stansbery in 1970 was followed by the successful transplant efforts of Ahlstedt (3) ultimately keeping Io off the endangered species list (4).

Second Place, Tennessee Region
Bogan. A. E., & P.W. Parmalee. 1983. Tennessee’s Rare Wildlife, Volume II: The Mollusks. Tennessee Wildlife Resources Agency, Nashville. 123 pp.

The only Tennessee drainage freshwater gastropods to reach the Federal list have been Pyrgulopsis ogmorhaphe and Athearnia anthonyi, both in 1994. A review of the 5Aug93 issue of the Federal Register in which those two species were formally proposed for endangered status shows the work of Bogan and Parmalee cited prominently. This is certainly a much more complete work than that of Stansbery, although appearing later on the scene.

First Place, Alabama Region
Stein, C.B. 1976. Gastropods. Pp. 1-41 in Endangered and Threatened Plants and Animals of Alabama. H. Boschung (ed.). Bull. Alabama Museum of Natural History 2: 21- 41.

The first freshwater gastropod to enter the Federal Endangered Species list was Tulotoma magnifica in 1991. The review of Stein (1976) appears as the primary (published) reference in the 11July90 Federal Register proposing that endangered status. And even though at least four additional calls to alarm on behalf of the Mobile Basin fauna have been issued more recently (5), Stein's work may still be the most thorough.

Second Place, Alabama Region
Athearn, H. D. (1970) Discussion of Dr. Heard's paper. Malacologia 10: 28-31.

A batch of six Mobile Basin gastropods were added to the Federal list in 1998. The Federal Register of 17Oct97 cited six references in support of the statement that "During the past few decades, publications in the scientific literature have primarily dealt with the apparent decimation of this fauna" - Goodrich 1944, Athearn 1970, Heard 1970, Stein 1976, Palmer 1986, and Garner 1990. The work of Goodrich 1944 is a bit old for our fifty-year window, but the Athearn 1970 / Heard 1970 pair certainly does seem to have had an impact.

These papers were both contributed to that same (1968) symposium that also featured the Stansbery paper cited above. Bill Heard’s paper, entitled "Eastern freshwater mollusks, the South Atlantic and Gulf Drainages," was rather vague and general. But the "Discussion” by Herb Athearn, appearing in print as a simple four page list of "now rare and endangered, or possibly extinct" species, seems to have had a significant influence on Carol Stein's more complete review and the regulations that followed in the 1990s.

Northeast
Harman, W. N. & J. L. Forney (1970) Fifty years of change in the molluscan fauna of Oneida Lake, New York. Limnology & Oceanography 15: 454-460.

The quality of the science in all four of the works cited for Tennessee and Alabama above is anecdotal at best. In fact, the papers of Stansbery and Athearn do not even rise to the level of the anecdote. For their 1970 paper in L&O, by contrast, Harman and Forney rigorously resampled Oneida Lake at the same spots originally sampled by F. C. Baker in 1917 (6), using similar gear. They documented significant reductions in gastropod abundance, species richness and diversity, and striking faunal shifts with the introduction of the invasive Bithynia tentaculata.

Harman and Forney’s work inspired me as a graduate student to reanalyze Baker’s data for a paper I published in The American Naturalist in 1981 (7), carrying forward to Chapter 9 of the book I published in 2000 (8). Harman also followed his 1970 study with a third study in 1992-95, documenting another 31% reduction in species richness with the introduction of zebra mussels (9).

Nominally driven to extinction in the 50 years between 1917 and 1967 were three nominal species nominally endemic to Oneida Lake, Amnicola bakeriana, A. clarkei, and A. oneida. Henry Pilsbry differentiated these three taxa from other much more widespread hydrobiids on the slenderest of threads (10). Nevertheless, the phantom New York hydrobiids of Baker and Pilsbry are no less valid than the phantom Alabama pleurocerids that Athearn listed without comment down the left margin of Malacologica Volume 10 in 1970 (11).

But Harman’s call to alarm has been of no consequence to freshwater gastropod conservation whatsoever. That a rigorous work of scientific research should disappear completely from the public conscience, while an unsubstantiated faunal list reaches the Federal Register to impact the laws of the land, should surprise none of my faithful readership (12). Science and Public Policy are two entirely different things.

Pushing on in the former, nonetheless,
Rob

Notes

(1) Stansbery, Clarke, Heard, Athearn, Dwight Taylor, Murray, Clench, Dundee, Allyn Smith, Abbott, Rosewater, Keen, Emerson, and Joe Morrison.

(2) Stansbery, D. H. (1972) The mollusk fauna of the North Fork Holston River at Saltville, Virginia. Bull. AMU 1972: 45-46. Stansbery, D. H. & W. J. Clench (1974) The Pleuroceridae and Unionidae of the North Fork Holston River above Saltville, Virginia. Bull. AMU 1974: 33-36. Stansbery, D. H. & C. B. Stein (1976) Changes in the distribution of Io fluviatilis in the upper Tennessee River system. Bull AMU 1976: 28-33.

(3) Ahlstedt, S. A. (1991) Reintroduction of the spiny riversnail Io fluvialis into the North Fork Holston River, southwest Virginia and northeast Tennessee. Amer. Malac. Bull. 8: 139-142.

(4) The reintroduction of Io into the NF Holston depended on much more than a few papers in the Bulletin of the AMU. The snails (and indeed, most of the benthic fauna of the river) were eliminated by pollution from the Olin-Mathieson Chemical Company in Saltville, which was closed by the EPA in 1971-72. Our good friend Steve Ahlstedt tells me that his Io transplant project was an outgrowth of water quality monitoring projects that started in the mid-1970s with mussels in barbeque baskets.

(5) Mobile Basin I: Two Pleurocerids Proposed for Listing [24Aug09]

(6) Baker, F. C. (1918) The productivity of invertebrate fish food on the bottom of Oneida Lake, with special reference to mollusks. NY State Coll. Forestry Tech. Publ. 9. 264 pp.
For more about this remarkable man and his work, see
The Legacy of Frank Collins Baker [20Nov06]

(7) Dillon, R.T. (1981) Patterns in the morphology and distribution of gastropods in Oneida Lake, New York, detected using computer-generated null hypotheses. American Naturalist 118: 83-101. [PDF]

(8) Now available in paperback! [Dillon 2000]

(9) Harman, W. N. (2000) Diminishing species richness of mollusks in Oneida Lake, New York State, USA. Nautilus 114: 120-126.

(10) Pilsbry, H. A. (1918) New species of Amnicolidae from Oneida Lake, New York. pp 244-246 in F. C. Baker, cited in (6) above. We'll never know, but from Pilsbry's descriptions it looks to me like Amnicola bakeriana may be a synonym of A. limosa, Amnicola clarkei is Lyogyrus granum, and Amnicola oneida is Marstonia lustrica.

(11) See my four-part series on the Mobile Basin pleurocerids:
I. Two Pleurocerids Proposed for Listing [24Aug09]
II. Leptoxis Lessons [15Sept09]
III. Pleurocera Puzzles [12Oct09]
IV. Goniobasis WTFs [13Nov09]

(12) See for example: Red Flags, Water Resources, and Physa natricina [12Mar08] and references cited therein.

TRUE CONFESSIONS: I Described a New Species

Editor's Note.  This essay was subsequently published as: Dillon, R.T., Jr. (2019b) TRUE CONFESSIONS: I described a new species.  Pp 193-198 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston.

... or, to deflect at least a fraction of the calumny, two accomplices and I described a new species. A pdf of the recent description of Physa carolinae by Wethington, Wise, and Dillon can be downloaded from note (1) below.

The existence of dark, slender populations of Physa in the Charleston area was first called to our attention in the 1980s by the late Julian Harrison, a colleague on The College faculty, primarily a herpetologist but an excellent all-round naturalist. The sample he brought us came from a shallow, swampy pond on James Island, in suburban Charleston. I told him these were simply "Physa heterostropha," which is what I called all the local Physa populations twenty years ago.

A couple years later Amy Wethington and I discovered a second population of slender, dark Physa in an agricultural ditch on Johns Island, about 10-15 km south of the city. We were working on a population genetic study designed to evaluate barriers to dispersal among sea islands (2), and needed to find a Physa population in an extensive region of sod farms to complete our (rather tightly specified) sampling grid. On the map, this part of Johns Island looked most unpromising. Sod farms are heavily fertilized and irrigated, ditched and drained into collecting ponds, brutally hot in the summer and exposed in the winter. But sure enough, in a damp and weedy ditch in the middle of Johns Island [right, below], Amy and I found another population of strikingly dark, slender Physa.

Intriguingly, this dark slender morphology seemed to have a strongly heritable component. Lab lines of the “Johns Island Physa” retained their distinct appearance to the second and third generations in culture. In the mid-1990s I did some experiments (as yet unpublished, shame on me) to estimate the heritability of shell shape (six linear measures) by regressing F1 hybrids between the Johns Island line and our standard (fatter) Physa lines on their mid-parent values. The heritability of shell morphology was strikingly high, but I digress.

The F1 hybrids derived from that experiment failed to reproduce. In retrospect, these observations probably influenced the first set of studies Amy and I designed to test reproductive isolation in Physa (3). We studied two populations of Physa heterostropha, two populations of P. integra, and two populations of P. acuta because (we imagined) that we’d find some reproductive isolation within species, as well as reproductive isolation between nominal species. We didn’t find any reproductive isolation among any of these six populations, of course, prompting us to synonymize most of the world’s Physa populations under the single nomen, Physa acuta.

Wait, wait! Does Rob Dillon have the arrogance to assert that dozens (scores?) of specific physid nomina (4) recognized by the entire community of systematic biologists around the world for 200 years are all synonyms of a single, variable, cosmopolitan Physa acuta, while in some ditch ten kilometers south of Charleston lives a bona fide undescribed species that only Rob Dillon can recognize? Let’s back up and get a fresh start.

The taxonomy of the North American Physidae in currency when Amy and I began our research program in the late 1980s was that of George Te, as reproduced in Burch’s "North American Freshwater Snails." Had I sent my dark, slender Physa to Te while he was still active in the 1970s, I feel fairly certain that he would have identified them as "Physella hendersoni" (5), the type locality of which is in Yemassee, SC, just 80 km west of Charleston. Burch's figure 677, labeled "Physella (Costatella) hendersoni ssp," does indeed appear to depict a slender shell quite similar to that borne by our Johns Island population.

But in another of those serpentine turns for which freshwater malacology is so famous, “hendersoni” was originally described by Clench (1925) as a subspecies of Physa pomilia Conrad (1834). Te considered pomilia to be a subspecies of P. heterostropha while holding hendersoni distinct. Working with snails sampled from their type localities, however, our 2007 breeding studies demonstrated both that hendersoni and pomilia are conspecific, as Clench originally suggested, and that pomilia/hendersoni most certainly is reproductively isolated from heterostropha/acuta (6).

And our dark, slender physids (which we began calling "Physa Species A" about ten years ago) are reproductively isolated both from pomilia/hendersoni and from acuta/heterostropha. The paper immediately preceding the description of these populations as Physa carolinae is a Dillon (solo) work documenting F1 hybrid sterility between carolinae and acuta, and both sexual isolation and apparent hybrid inviability between carolinae and pomilia (7).

So yes, as embarrassing as it looks – the research group responsible for synonymizing the physid fauna of the entire continent from about 40 nominal species down to maybe ten (8) is now asserting that we have discovered a Physa species overlooked by everybody, in our own back yards.

Physa carolinae seems seasonally common and widespread throughout the Atlantic Coastal Plain, ranging at least from Virginia to Georgia. We do not have any original field observations further south, but a glance through the collections of the Florida Museum of Natural History a couple years ago suggested to me that Physa carolinae may also be widespread in Florida, museum lots generally catalogued under the specific nomen "hendersoni."

Throughout its range, P. carolinae is most commonly found in swamps, ditches, and other waters of an intermittent or vernal character. It seems to be a southeastern ecological analogue of Aplexa – the two taxa converging on each other in habitat, life history, and morphology.

This Saturday just past Amy, John Wise, and I were featured in the Charleston newspaper as "Snail Sleuths - CofC Researchers Find Lowcountry Species" (9, 10). In addition to some cutesy quotes about the pace of snail research being - well - slow, I found myself saying something like this to the reporter: "We send scientists all over the world, and we don't know the slugs under our own trash cans." If anybody on this list is aware of any funding agencies that might be responsive to such an appeal, please bring them to our attention at your earliest convenience.

And keep in touch,
Rob

Notes

(1) Wethington, A.R., J. Wise, and R. T. Dillon (2009) Genetic and morphological characterization of the Physidae of South Carolina (Pulmonata: Basommatophora), with description of a new species. The Nautilus 123: 282-292. [PDF]

(2) Dillon, R.T., and A.R. Wethington (1995) The biogeography of sea islands: Clues from the population genetics of the freshwater snail, Physa heterostropha. Systematic Biology 44:401-409. [PDF]

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

(4) Wethington, Wise & Dillon listed 19 nomina in their P. acuta synonymy, including heterostropha, integra, the western virgata, and the more tropical cubensis. Also listed was P. natricina, about which I offered an entire essay on 12Mar08.

(5) I swapped several letters with George Te in 1976, while I was still an undergraduate at Virginia Tech. He identified the Physa acuta I sent him from the New River as "P. hendersoni," and my Physa gyrina as "P. pomilia."

(6) Dillon, R. T., J. D. Robinson, and A. R. Wethington (2007) Empirical estimates of reproductive isolation among the freshwater pulmonates Physa acuta, P. pomilia, and P. hendersoni. Malacologia 49: 283 - 292. [PDF]

(7) Dillon, R. T. (2009) Empirical estimates of reproductive isolation among the Physa species of South Carolina (Pulmonata: Basommatophora). The Nautilus 123: 276-281. [PDF]

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

(9) Snail Sleuths: CofC researchers find lowcountry species
Charleston Post & Courier 3April2010

If the link above expires, go to the FWGNA archives:
Post&Courier3Apr2010

(10) And I'm now starring on YouTube! Check it out:
http://www.youtube.com/watch?v=wTzgv5sxFRQ

The Hazards of Unprotected Malacology

On March 13, nature writer Nick Mirro posted the following query to the MOLLUSCA listserver:

I hate to show my ignorance here, but… Are there any or many North American fresh water gastropod or bivalve species that could potentially transmit disease to human by skin (hand) contact? I am asked this question all the time and am not confident in my stock answer, which is, “no but wash your hands anyway.” We are in north central Texas. Thanks.

Here, for the general entertainment of our group, is my reply:

--------------
Dear Nick,

No, you're not "showing your ignorance!" That's such an interesting question, I'm going to answer it four times.

1) Nah, don't worry about it. I've hand-collected freshwater mollusks all over North America for 40 years, and never given it a second thought.

2) Well, actually, some very widespread freshwater mollusk species can thrive in polluted environments. I've seen strikingly high densities of Physa acuta, Lymnaea humilis, and the pisidiid clam Musculium transversum downstream from sewage treatment plants. (Unionids, not so much!) It might be a good idea to wash your hands after pulling anything from such waters - rocks, bottles, beer cans, snails or clams included. There was a little scare in the Myrtle Beach area a summer ago when state wildlife officials advised residents of a trailer park not to handle Pomacea insularum introduced into a nasty drainage pond in their neighborhood. See my blog post of 14Aug08* to read more.

3) Several years ago I visited Northern Michigan to sample Physa parkeri** from the lovely waters of Douglas Lake, at the University of Michigan Biological Station. I made my collection in a one-gallon thermos jug, planning to transport the sample back to Charleston alive. The next morning I was disappointed (but perhaps not terribly surprised) to discover that quite a few individuals had expired. So I reached into the jug (repeatedly) to remove the dead individuals for preservation, leaving the live ones undisturbed. Here's the case of schistosome dermatitis ("swimmers itch") that resulted.

4) Nah, don't worry about it. I never do.

Cheers,
Rob

Notes


*Two dispatches from the Pomacea front [14Aug08]

**Physa parkeri turned out to be an ecophenotypic variant of Physa gyrina. See Dillon & Wethington (2006) The Michigan Physidae revisited: A population genetic study. Malacologia 48: 133-142. [PDF]

Grand Opening!

It's not unusual for retail stores to open their doors for business, operate for a few weeks, and then announce a "Grand Opening." I'm not sure about the rationale for this practice, but welcome to the Grand Opening of the FWGNA Blog! Doing business since July, 1998.

For any newcomers who might stumble onto this post - the Freshwater Gastropods of North America project was born at the first World Congress of Malacology in Washington, 12 years ago this summer. Our objective has always been to survey the entire continent for freshwater snails, by any means necessary. Four states mostly done as of February 2010! What a team!

In any case, very early in the effort I fell into the habit of sending mass emails to an ever-growing addressbook of colleagues - 186 at last count - recently about once per month*. Often these messages have been simple news items about upcoming meetings, grants, employment opportunities, or whatever. But increasingly I've found myself reviewing and reporting on the current literature, offering opinions on taxonomic questions, and pontificating on invasive species, endangered species, and matters at the interface between science and public policy.

Clearly we've needed a medium to open up a better conversation for a long time. I'm not sure why I didn't migrate to the blog format years ago.

An important (although perhaps secondary) benefit of modern blogging is the convenience of the indexing function. So over the last couple weeks I've uploaded (from the "FWGNA Archives") the great majority of my old email posts, "tagging" them as I did with the brief descriptors you see listed at right. And I imagine you've noticed the Google-powered search box. It may take a while for the Google webcrawlers to find this tiny corner of the internet and "populate" that search box, but eventually it should become a helpful tool.

And now its up to all of us to give those web-crawlers something to feed on! Regarding comments - I am advised that, unless I moderate this blog, unscrupulous agents will use the blank spaces provided to advertize viagra. But you do not need a Google account to comment. Type your message in the comment box, and choose "name" in the "select profile" box, or even "anonymous" if you want. I'll get an email alerting me that a comment needs my approval, and do so promptly.

Looking forward to it,
Rob


*I'm still planning to maintain my email list, and I guess I'll continue to send monthly emails. But they'll be short - probably just a title and a link to the blog.