Dr. Rob Dillon, Coordinator

Friday, December 18, 2009

Community Consequences of Bellamya Invasion

To the FWGNA group:

I dearly love experiments. Does it seem to anybody else on this list that, over the last 20-30 years, the experiment is going out of style? In any case, the recently published research results of Pieter Johnson, Chris Solomon, and their colleagues on the community effects of Bellamya (1) invasion, which include both experimental and field components, arrive as especially welcome contributions to our (surprisingly slender) file on the biology of invasive viviparids.

Bellamya populations (2) seem to have appeared in the Northern Highlands lake district of Wisconsin sometime in the 1950s. Johnson and his colleagues (3) conducted an 8-week experiment in a set of 24 outdoor “mesocosms” containing 1,000 of water from nearby Sparkling Lake, a clean sand/gravel substrate (inoculated with lake mud), two cinder block “refugia,” and 45 individuals each of Physa gyrina, Lymnaea stagnalis, and Helisoma trivolvis. Eight of the mesocosms received 45 Bellamya, eight received a pair of crayfish (4), eight received both Bellamya and crayfish, and eight were held as controls.

The most striking result of these experiments was that the populations of Physa and Lymnaea grew in the absence of Bellamya, but declined in the presence. The control Physa roughly doubled in population size over the 8 weeks, while the control Lymnaea roughly doubled in wet mass, although apparently did not reproduce (5). But all pulmonate populations declined by all measures in the Bellamya treatments. Clearly the invasion of Bellamya through the lakes of Northern Wisconsin should have negative effects on the native freshwater gastropods, right?

Well, of course it’s more complicated than that. The Helisoma populations declined in both biomass and abundance (5) in all mesocosms, including the controls. Whether the Helisoma were outcompeted by the Physa and Lymnaea, or whether these mesocosms were simply unsuitable habitat for Helisoma, we'll never know. My intuition suggests to me that if the researchers had floated some macrophytic vegetation on the surface of their mesocosms, their Helisoma populations would have been fine (6). The problem is that the experiments of Johnson and colleagues show Helisoma going to extinction in the absence of Bellamya just as clearly as they show Physa and Lymnaea going to extinction in the presence (7). As much as I love experiments, a 5’ x 5’ structural foam plastic tank and a lake are two entirely different things.

Who could disagree? Certainly not our colleagues in Wisconsin. Thus in a companion study, Chris Solomon and a gang of four (including yours truly) surveyed 42 lakes in northern Wisconsin, roughly half of which had been invaded by Bellamya and half not, collecting a great variety of environmental measures in the process (8).

We found evidence of positive correlations between the presence of Bellamya and several general measures of lake productivity, such as conductivity and Secchi turbidity, but very little evidence of an effect of Bellamya on the native freshwater gastropod fauna. At neither the site level nor at the lake level could we find any evidence that Bellamya presence or abundance had any effect on the native freshwater gastropod community at all.

The absence of any significant results whatsoever neatly confirms my hypothesis, of course. Casting an eye back through the FWGNA archives, it looks as though I’ve authored fully 13 previous posts on invasive species, primarily Pomacea, Potamopyrgus, and Bellamya, with other viviparids and Bithynia making cameo appearances. And it may be recalled that I am an advocate of the “empty niche” hypothesis, which dates me back to the 1970s with most embarrassing accuracy.

Essentially, I think that the two best predictors for the success of a potential invasion are that the invading population must be weedy and different (9). Invaders must be adapted to the new environment they are invading, of course, while ecologically different from the native inhabitants – the more different, the better.

The gigantic, filter-feeding, ovoviviparous Bellamya is indeed strikingly different from all the other elements of the freshwater gastropod community native to northern Wisconsin. Hence I would not expect to uncover any competitive effects, and feel quite validated that we did not find any.

But I hasten to add two asterisks. First, populations of four different species of viviparids inhabit the lakes of northern Wisconsin, three of which are gigantic, filter-feeding, ovoviviparous invaders: Bellamya chinensis, B. japonica, and Viviparus georgianus. That our distributional data returned no evidence of a negative relationship within this subset, over 197 sites in 42 lakes, does indeed seem to suggest that our methods may have been too weak to detect even bona fide competition, where it occurs.

Second, a special challenge attends the selection of any invasive species for a study of population biology. What would make the researcher think that any such population has reached the carrying capacity of its environment? Competition cannot begin until some resource becomes limiting. If both Bellamya and Viviparus populations are still growing and spreading through northern Wisconsin in 2009, there is no reason to imagine that either will have any effect on the other.

And in fact, our analysis did return evidence of correlations between Bellamya presence and such measures of disturbance such as boat landings and shoreline housing. This implies to us that Bellamya populations may indeed be actively growing and spreading even in northern Wisconsin, where the invasion may have been ongoing for as much as 50 years.

I conclude with a call for additional research (10). This is a button you have rarely seen me push in this series of essays, both because it is trivially obvious to me that we need additional research on all aspects of freshwater gastropod biology, and because I try not to preach to the choir.

But where other people see "invasive species," I see "model organism." We have been greatly enriched, for example, by a huge volume of first-rate research on Pomacea in recent years (11), and that literature is huge (12). Meanwhile I haven't seen more than a couple papers published on even the most basic aspects of the life history of Bellamya, in total, over the 100-year history of the North American invasion (13). And three paragraphs ago I found myself offering an hypothesis regarding carrying capacities of invasive viviparids without a single estimate of population size, even static, ever taken anytime, anywhere. As easy as invasive viviparids are to sample, sitting on clean sand at the bottom of bathtub reservoirs? Shame on us all!

Keep in touch, everybody!

(1) I follow Smith (2000) in preferring the (internationally-recognized) generic nomen "Bellamya" over the (provincial) "Cipangopaludina." See the FWGNA page on B. japonica for details and references.

(2) Wisconsin populations are almost entirely Bellamya chinensis. I did identify B. japonica in five (of 42) lakes surveyed, which were lumped with B. chinensis for analysis. That's B. chinensis on the left, and B. japonica on the right.

(3) Johnson, P. J., J. D. Olden, C. T. Solomon, and M. J. Vander Zanden (2009) Interactions among invaders: community and ecosystem effects of multiple invasive species in an experimental aquatic system. Oecologia 159: 161-170.

(4) The crayfish were the invasive Orconectes rusticus. Those results were interesting as well, but don’t bear directly on the subject of this essay.

(5) Pulmonate juveniles are born at approximately 1 mm shell length. The sampling problems of finding such “speck babies” in a 1,000 liter mesocosm with sand and cinder blocks should be obvious to everybody. Thus I strongly suspect the “pulmonate abundance” figures reported by Johnson and colleagues are systematic underestimates.

(6) Helisoma is certainly quite commonly observed on floating vegetation. Any sort of additional habitat along these lines would certainly have benefited all three pulmonate populations.

(7) And if there’s a crayfish in the lake, all pulmonate populations are immediately doomed.

(8) Solomon, C. T, J. D. Olden, P. T. J. Johnson, R. T. Dillon and M J. Vander Zanden (2010) Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes. Biological Invasions 12: 1591 - 1605. [PDF] 476kb.

(9) "Invaders Great and Small" Post of September '08.

(10) This should not be construed as a call to sequence two genes from single individuals sampled from 40 imaginary viviparid species in a vain attempt to reconstruct evolutionary events of 100 million years ago, while remaining arrogantly clueless regarding the basic population genetics of even one crappy pond full of crappy snails today.

(11) "Ampullariids star at Asilomar" Post of August '05.

(12) "Review: Global Advances in Golden Apple Snails" Post of May '07.

(13) Stanczykowska, A, E. Magnin and A. Dumouchel (1971) Etude de trois populations de Viviparus malleatus (Reeve) de la region de Montreal. I. Croissance, fecondite, biomasse et production annuelle. Can. J. Zool. 49: 1431-1441. Jokinen, E.H. (1982) Cipangopaludina chinensis (Gastropoda: Viviparidae) in North America, review and update. Nautilus 96: 89-95. Therriault, T. W. and E. Kott (2002-3) Cipangopaludina chinensis malleata (Gastropoda: Viviparidae) in southern Ontario: An update of the distribution and some aspects of life history. Malac. Rev. 35-36: 111-121.

(1) From John Havel JohnHavel@MissouriState.edu
Hi Rob,

Since I’m a newcomer to snail research (although an old hand at invasions), I was hesitant to reply to all. So, below are my comments on your most-interesting essay. I plan to work again next spring and summer at Trout Lake. Doing some quantitative sampling for densities and fecundity patterns could be interesting. Care to join me for part of the venture?

Nice review of the papers by Johnson et al. (2009) and Solomon et al (in press). By the way, in last summer’s experiments with a former student, I also found very little effect of Bellamya on Physa growth rates in the laboratory (Clark and Havel, unpublished data).

See also the paper of Pattinson et al. (2003) on invasive Daphnia. We discuss the same empty niche hypothesis as important for tropical D. lumholtzi invading reservoirs of the south-central US.

I don’t agree that Bellamya are that different in dominant feeding ecology from native gastropods. After all, Bellamya are well known to clean surfaces quite thoroughly, and are for sale by breeders on the internet for cleaning ornamental ponds. Perhaps more important is whether or not resources are indeed limiting. (Although I now see that you consider this later in your essay.)

Regarding your statement about Bellamya being a "model organism." I agree! Lots of ways to study general ecology principles. [e.g., see papers by Havel and Shurin (2004) and Havel et al. (2005)]

Your assertion that we are "without a single estimate of population size, even static, ever taken anytime, anywhere" is an exaggeration, of course. See Solomon et al. (2009): quantitative sampling (see methods par. 4) plus population density estimates (results par. 5). But, I agree that population and fecundity estimates would be useful for better understanding these study systems and the potential of exotic viviparid snails for population growth and expansion.

But regarding your suggestion that viviparids might be easy to sample, "sitting on clean sand at the bottom of bathtub reservoirs," lakes can be spatially very complex (macrophytes, rocks, sand, logs, leaf litter, flocculent organics). I found quantitative sampling to be a real challenge; but then I’m new to the benthos. (I could definitely use some help with these techniques.)

Additional references
Havel, J.E., and J.B. Shurin. 2004. Mechanisms, effects, and scales of dispersal in freshwater zooplankton: a synthesis. Limnology and Oceanography 49: 1229-1238. Havel, J.E., C. E. Lee, and J. Vander Zanden. 2005. Do reservoirs facilitate invasions into landscapes? BioScience 55: 518-525. Pattinson, K.R., J.E. Havel, and R.G. Rhodes. 2003. Invasibility of a reservoir to exotic Daphnia lumholtzi: Experimental assessment of diet selection and life history responses to Cyanobacteria. Freshwater Biology 48: 233-246.

(2) From David Campbell amblema@bama.ua.edu
Regarding Smith's (2000) preference for the generic nomen "Bellamya," unfortunately, he's led you astray. The type of Bellamya is from West Africa, and no East Asian species belongs in it (even if you put them in the same genus, there are older names both from Africa and from Asia). See... Mita E. Sengupta, Thomas K. Kristensen, Henry Madsen, Aslak Jørgensen. 2009. Molecular phylogenetic investigations of the Viviparidae (Gastropoda: Caenogastropoda) in the lakes of the Rift Valley area of Africa. Molecular Phylogenetics and Evolution 52:797–805 ...for the molecular data, though they don't deal with the nomenclatural implications, except for incorrectly suggesting that Neothauma should be included in Bellamya- Neothauma is the older name. It's still possible that some other name applies besides Cipangpaludina, but to determine that requires actually checking the type species of the nominal Asian genera.

(3) From Jeremy Tiemann jtiemann@inhs.uiuc.edu
Have you seen this paper yet? Bury, J.A. B.E. Sietman, and B.N. Karns. 2007. Distribution of the non-native viviparid snails, Bellamya chinensis and Viviparus georgianus, in Minnesota and the first record of Bellamya japonica from Wisconsin. Journal of Freshwater Ecology 22(4):697-703.

(4) From Bob Prezant prezantr@mail.montclair.edu
Rob, I agree...a "model organism" is just what we have in Bellamya. Can't remember if I sent this article to you. Hope you're warmer than we are here in NJ. Prezant, R. S., E. J. Chapman and A. McDougall (2006) In utero predator-induced responses in the viviparid snail Bellamya chinensis. Canadian Journal of Zoology 84: 600-608.

Friday, November 13, 2009

Mobile Basin IV: Goniobasis WTFs

To the FWGNA group:

Georgia is just Florida, one state north and 65 million years back. During the Cretaceous Period, most of the land mass that constitutes the present Mobile Basin of Alabama would have been obscured by a shallow sea and the occasional shadow of a passing mosasaur. The exception would have been a peninsula in what is today North Georgia (1).

Atlanta sits in the middle of that Cretaceous peninsula, General Sherman notwithstanding (2). The low hills to its east drain through the Ocmulgee/Oconee/Altamaha to the Atlantic. The Chattahoochee River runs through the middle of the city, under the I-285 beltway and southwest to the Gulf. To its immediate north lie tributaries of the Alabama/Coosa, draining into the Mobile Basin. And just a bit further north, the waters of the Tennessee River flow into the Mississippi (below, 3).

An appreciation of the complex drainage patterns of north Georgia will be important for an understanding of the hypotheses I am preparing to advance in this essay. If you are planning an earnest attempt to follow me, you will need to hold in your mind that the Coosa River is formed at the Georgia/Alabama line by the junction of two major tributaries, the (more northern) Conasauga/ Coosawattee/ Oostanaula and the (more southern) Etowah (4). And I do apologize for the drainage taxonomy. Subsequent to the departure of the mosasaurs, but prior to the arrival of Sherman, this part of the world was infested with dozens of Indian tribes, vying among one another in the unpronouncability of their names. After extinguishing each tribe, the European settlers named a local river in its honor, apparently careless of how, or even whether, any of these rivers might ultimately interconnect.

In any case, the diversity of the Goniobasis fauna of the Alabama/Coosa river system might aptly be described as "legendary." Goodrich (1936) recognized 24 species in the main river itself, and subsequently (1941) added about 11 species from "small streams." His final (1944) tally for the entire fauna of the Coosa River system listed, from rivers of all size, 29 species of Goniobasis, many with subspecies (5).

As patient and perceptive readers of this series of essays may have by now gathered, I myself have relatively little field experience anywhere in the Mobile Basin. What insight I have gathered regarding the pleurocerid fauna of the Oostanaula side of the Coosa has developed as a consequence of my work in east Tennessee on Goniobasis clavaeformis / Pleurocera unciale, as featured in last month’s (6) “Mobile Basin III.” When first I crossed the low hills that separate the Hiwassee system of the Tennessee River from the Mobile Basin in North Georgia, and peeked tentatively into the famously diverse waters of the Oostanaula subdrainage, I was shocked by the sight that met my eyes. WTF?!

This was the same pleurocerid fauna I had just spent the previous week sampling in Tennessee. In Cohulla Creek, one of the main tributaries of the Conasauga/Oostanaula east of Dalton, I recognized three old friends: Goniobasis simplex, G. troostiana (or "arachnoidea"), and G. clavaeformis – the same species widespread from southwest Virginia down the width of east Tennessee. The only difference was that clavaeformis was now called vestita, arachnoidea was now called striatula, and simplex was now called, well, I don't know (7). And the allozyme data I have subsequently collected seem to show that I was correct.

But it had happened before. My first “WTF moment” in the upper Mobile Basin actually occurred in the mid-1990s, kneeling beside the Etowah River. On that occasion I had been sampling west from the Atlantic drainages of central Georgia, crossed the broken Piedmont north of Atlanta, and found essentially the same G. catenaria I’d I had spent most of my professional career chasing through southern Virginia and the Carolinas, now re-named “Goniobasis caelatura” in the Etowah. And the DNA sequence data I have subsequently gathered with the help of my colleague John Robinson again seem to show that this impression was correct (8).

So we’ve now reached the point of a hypothesis – not just for this essay, but for all IV essays in this series. The endemicity of the Mobile Basin pleurocerid fauna has historically been much overstated. As the Cretaceous seas receded, the pleurocerid faunas that colonized the Mobile Basin were a mixture of the Atlantic (older) elements and the Tennessee (younger) elements, both previously inhabiting a peninsula in north Georgia. These faunas can still be seen today in the two major tributaries of the Coosa – the southern Etowah and the northern Oostanaula.

But don’t misunderstand me. There are bona fide endemic species of pleurocerid gastropods in the Mobile Basin. Dykes Creek is a lovely little stream running directly into the main Etowah River very near its junction with the Oostanaula. It is inhabited by (at least) three species: a G. clavaeformis-type from the Tennessee side (A), a chunky G. catenaria from the Atlantic side (B), and a species I'm going to call "WTF3" (C). Allozyme data show WTF3 to be genetically similar to G. catenaria, but reproductively isolated from it. My best guess is that Goodrich would have identified WTF3 as the subspecies Goniobasis caelatura sternsiana (Call 1886). But if so, that's the second of his caelatura "subspecies" that needs to be raised back up to the full species level (9). I am quite sure, in any case, that WTF3 is endemic to the Mobile Basin. And perhaps very rare.

So to summarize. In late June the US Fish and Wildlife service proposed endangered status for two Mobile Basin pleurocerids species, "Leptoxis foremani" and "Pleurocera foremani" (Essay I, 24Aug 09 - see note 10). The former nominal species is likely a local population of L. picta, which is not protected in any way (Essay II, 15Sept - see note 11). The latter nominal species is likely a local ecophenotypic variant of the most widespread pleurocerid in the American southeast (Essay III, 12Oct - see note 6). Meanwhile genuinely endemic and probably rare species go entirely unrecognized by anybody.

Science and public policy are two entirely different things. What I have been demonstrating over this four part series is science - the construction of testable hypotheses about the natural world. This process, this vocabulary, this way of looking at the world, is entirely different from the process that brought the US Fish & Wildlife Service to propose its endangered species regulations in the 29Jun09 Federal Register. These two ways of looking at the world are not compatible, nor are they incompatible. FWS biologists play baseball, I play the banjo. Neither is better, neither is worse.

I am not suggesting that the FWS drop "Leptoxis foremani" and "Pleurocera foremani" like a pair of old girlfriends and drive Dad's Chrysler up to Dykes Creek with flowers and bonbons to court G. stearnsiana, or whatever TF it is. Everything I've offered in this essay is a hypothesis (12), and may change tomorrow. What I am suggesting is that if it is the genuine Will of the People that public resources be expended on science (13), all government agencies involved (regardless of mission) must support what has heretofore been marginalized as "basic research," such as that which produced the hypotheses I have advanced above, which is, after all, the only real Science there is. In other words - send me money, and leave me TF alone.

I'm waiting,


(1) The best treatment of this subject I've been able to find on the web is at NOAA, interestingly: Beach Nourishment, A Guide for Local Government Officials

(2) Literally.

(3) I've stolen this map from the "Southeast Watershed Assistance Network."

(4) And here's the map of the Mobile Basin drainage system that I stole for Essay I in this series. You might want to open it in a new window.

(5) Goodrich, C. (1936) Goniobasis of the Coosa River, Alabama. Misc. Publ. Mus. Zool. Univ. Mich., 31, 1-60. Goodrich, C. (1941) Pleuroceridae of the small streams of the Alabama River system. Occas. Pprs. Mus. Zool. Univ. Mich., 427, 1-10. Goodrich, C. (1944) Pleuroceridae of the Coosa River basin. Nautilus, 58, 40-48.

(6) "Mobile Basin III: Pleurocera Puzzles." Post of October '09.

(7) This is actually one of the biggest mysteries in my mind regarding the Goniobasis of the Alabama/Coosa. What did Goodrich (and everybody else who has ever sloshed through these rivers) call plain old, ordinary, vanilla, dirt-common Goniobasis simplex? I can't match it to a synonym on anybody's list, over 150 years of surveys. Has it been missed?

(8) "The Snails the Dinosaurs Saw." Post of March '09.

(9) In the mid-1990s I also recognized Goniobasis georgiana in the Etowah, another older-Appalachian species ranging through the upper tributaries of the Hiwassee in the North Carolina mountains. Goodrich lowered this nomen to subspecific rank as "G. caelatura georgiana," but its co-occurrence in the Etowah with what (I suppose) he would have identified as G. caelatura caelatura, absent any evidence of hybridization, suggests strongly that G. georgiana is a distinct species.

(10) "Mobile Basin I: Two pleurocerids proposed for listing." Post of August '09.

(11) "Mobile Basin II: Leptoxis lessons." Post of September '09.

(12) Thompson (2000, Walkerana 11:1-54) has a different hypothesis. In the words of my favorite Alabamian, "That's all I've got to say about that."

(13) And I'm not sure it is!

Monday, October 12, 2009

Mobile Basin III: Pleurocera Puzzles

To the FWGNA group:

Last month (1) we made passing reference to the Awakening of Calvin Goodrich, that 1934-41 period during which he published “Studies of the Gastropod Family Pleuroceridae” I – VIII (2). During this stage of his career, our hero developed his thesis that the characters upon which most pleurocerid taxonomy had been based - shell dimensions, coloration, ornamentation and so forth - are highly plastic and subject to environmental influence (3). In 2007 I coined the term “Goodrichian taxon shift” to describe situations where a single population of pleurocerids might vary down an environmental gradient to such an extent that taxonomists have recognized two different species (4). Or perhaps even two different genera?

I realize that the heading at the top of this essay is “Mobile Basin III.” But I beg your indulgence for the next three paragraphs to stray one drainage north, to the headwaters of the Tennessee River.

In my "Goodrichian" essay of 20Feb07 I reported unpublished observations on variation at two allozyme loci in a population of Goniobasis from Indian Creek, a tributary of the Clinch/Powell in southwest Virginia (5). In the headwaters, this single population of pleurocerids bore shells that were strongly carinate (historically referred to "G. acutocarinata" CA1), in middle reaches their shell morphology was smooth and typical of G. clavaeformis (C1), and upon joining the main Powell River, their shells became chunky and angulate, showing the morphology generally assigned the nomen “Pleurocera unciale” (P1).

In the last couple years I have extended this research program down the width of East Tennessee, to include populations from the Little River drainage near Maryville (figs CA2, C2, P2 at left), the Conasauga/Hiwassee near Etowah (figs CA3, C6, P3), and the Coahulla/Oostanaula/Coosa in North Georgia (figs CA4, P4). I have also sampled populations of G. simplex from each of these four regions to calibrate expected levels of interpopulation divergence at the 10 allozyme loci examined (fig S7).

The results of my 2007 study in Indian Creek are confirmed (6). Each of the four samples of “Pleurocera” was more genetically similar to the Goniobasis population just upstream than to any other sample of Pleurocera. Apparently taxonomists have been misled by ecophenotypic variation to identify populations of a single, widespread species under two different genera.

This result extends from the rivers of Tennessee into the Coosa drainage of North Georgia. Tradition has always held that elements of the Mobile Basin fauna are treated as endemic, even when indistinguishable from the fauna of neighboring drainages. Thus Goniobasis populations from small creeks in the Alabama/Coosa drainage showing the strongly carinate shell morphology are typically identified as “Goniobasis carinifera,” and those with heavier, smoother shells downstream as “Pleurocera vestitum.” Interestingly, if carinifera/vestitum is indeed conspecific with clavaeformis/unciale, the oldest name for the entire, sprawling species, from Virginia to Alabama, would be the Coosa name Goniobasis carinifera (Lamarck 1822).

In August we kicked this series off with news that the US Fish & Wildlife Service has proposed Alabama populations of pleurocerids identified as “Pleurocera foremani” for listing under the Endangered Species Act (7). According to the notice posted in the Federal Register, P. foremani is found today at only two locations, the lower Coosa River below Wetumpka Shoals and lower Yellowleaf Creek, a tributary of the Coosa (8). I understand from colleagues with field experience in this region that, sampling upstream, P. foremani is replaced by Pleurocera prasinatum in the smaller rivers, and that P. prasinatum is replaced by Pleurocera vestitum, and that vestitum is replaced by Goniobasis carinifera in the creeks.

In 1944, the mature Calvin Goodrich wrote regarding the Coosa species of Pleurocera, "On close study and comparison, they resolve themselves into four forms, and even these are not very distinctive. The specific names, in short, are to be considered conveniences in sorting rather than clean-cut differentiations" (9). He then went on to list P. vestitum "especially common in head streams," P. prasinatum "in the middle and lower Coosa," and P. foremani, which he distinguished by shell sculpture that "in one locality of the Cahaba is plainly a reversion, the same thing may be true of the shells of the Coosa.

"I have not seen the dissertation of Jeffrey Sides. But again referring to the 29Jun09 Federal Register (8), his sequence data suggested that P. foremani "was genetically more closely allied to a co-occurring species in the genus Elimia (Goniobasis)" than to any other species in the genus Pleurocera. Really? Even though double-digit sequence divergence is not uncommon within even conspecific populations of pleurocerids (10), the divergence between P. foremani and the local upstream Goniobasis appears to be of minor consequence?

Is the foremani/prasinatum/vestitum/carinifera taxon continuum in Alabama nothing but a unciale/clavaeformis/acutocarinata Goodrichian taxon shift, one state south? Has the US Fish and Wildlife service proposed federal protection for a local ecophenotypic variant of the most widespread pleurocerid in the American southeast? Pleurocera puzzles, indeed!

Stay tuned for more ...


(1) "Mobile Basin II: Leptoxis Lessons." Post of September '09 .

(2) A nice Goodrich bibliography is available from Kevin Cummings' website at the INHS

(3) "The Legacy of Calvin Goodrich." Post of January '07.

(4) "Goodrichian Taxon Shift." Post of February '07.

(5) Dillon, R.T. & J. D. Robinson (2007) The Goniobasis ("Elimia") of southwest Virginia, II. Shell morphological variation in Goniobasis clavaeformis. Report to the Virginia Division of Game and Inland Fisheries, contract 2006-9308. 12 pp. [pdf]

(6) I presented this research at a NABS symposium this May in Grand Rapids. A manuscript is currently in preparation. Dillon, R. T. (in prep) Genetic and morphological divergence among populations of pleurocerid snails inhabiting rivers of the Southern Appalachians: Evidence of a two-stage process.

(7) "Mobile Basin I: Two Pleurocerids Proposed for Listing." Post of August '09.

(8) Follow the link from the FWS Press Release: Service Proposes Endangered Species Status and Critical Habitat Designations for the Georgia Pigtoe Mussel, Interrupted Rocksnail, and Rough Hornsnail.

(9) Goodrich, C. 1944. Pleuroceridae of the Coosa River basin. Nautilus 58(2):40-48.

(10) "The Snails the Dinosaurs Saw." Post of March '09.

Tuesday, September 15, 2009

Mobile Basin II: Leptoxis Lessons

Through the early history of American malacology, the freshwater gastropod fauna of the Mobile Basin was not seen as exceptionally diverse. Isaac Lea, T. A. Conrad, and J. G. Anthony described about 20 species of Leptoxis (1) from the Mobile Basin from 1834 - 1860, for example, which Tryon (1873) boiled down to about 12 (2). This would not seem to be a significantly greater tally than the approximately 20 species of Leptoxis described from the Tennessee River system during that era.

Indeed, the apparent diversity of the Mobile Basin mollusk fauna may not so much be a consequence of evolutionary history, but rather history of a very human sort. It is best, perhaps, understood as the story of my professional hero, Calvin Goodrich (3).

Some of my audience may recall that Calvin Goodrich began his career as a newspaperman, and that he was influenced by A. E. Ortmann to take up malacology around the years 1913 - 1917. One of Ortmann's closest professional colleagues was Herbert H. Smith, who retired in 1903 from the Carnegie Museum in Pittsburgh to become curator of the Alabama State Museum in Tuscaloosa. When H. H. Smith died in 1919, a review of Smith's collections of Alabama pleurocerids was passed by Ortmann to Goodrich.

"The Anculosae of the Alabama River Drainage" was Calvin Goodrich's first substantial contribution to science (4). It is essentially a tribute to Smith (and indirectly to Ortmann), adding 11 new H. H. Smith nomina to a list of 14 transferred forward from Conrad, Lea, and Anthony. Goodrich described one new species himself, Anculosa smithi (named for guess who), bringing the total inventory up to 26 Leptoxis for the drainage. A concatenation of Goodrich's Plates I and II, illustrating all 26 species (5), is shown at left (and click to enlarge).

This work long predated Goodrich's (1934-41) "Studies on the Pleuroceridae," in which our hero came around to an understanding of the ecophenotypic nature of the shell morphological characters upon which pleurocerid taxonomy has historically been based. It also (of course) predated his (1939-1944) reviews of the Pleuroceridae of North America, in which Goodrich synonymized a huge fraction of the old 19th century taxonomy, combining (for example) the 26 nomina of Leptoxis (1) described from the Ohio/Tennessee basin down to nine (6). But apparently the old newspaperman could not edit his own copy. When he came back to the "Pleuroceridae of the Coosa River Basin" twenty years later (7), he preserved 18 Leptoxis species, saying, "A re-examination in 1943 has confirmed most of the decisions of 1922" (8).

By the 1940s, however, Calvin Goodrich's editorial skills were of little consequence to the Mobile Basin Pleuroceridae. Because as early as 1914 the first of seven dams was closed on the Coosa River, covering miles of the rocky rapids which were the habitat of Leptoxis with silty slackwater. And over the next 53 years, as the Coosa was almost completely impounded by Alabama Power, the Corps of Engineers was improving navigation on the Alabama River downstream with channelization, locks and dams.

Entering the 1990s, Leptoxis populations were believed to have survived in only four regions of the Mobile Basin - one tributary of the Black Warrior River (7), the upper reaches of the Cahaba River, the lower reaches of three mid-sized tributaries of the Coosa, and (amazingly) the main Alabama River downtream from the Claiborne Lock and Dam. Perhaps not surprisingly, conventional wisdom accorded snails from these four regions four different specific nomina - Leptoxis plicata, L. ampla, L. taeniata, and L. picta (respectively). The first three of these species were approved as candidate species in 1995, and after study and comment, entered the Federal lists in 1998 - L. plicata as endangered, L. taeniata and L. ampla as threatened (9). Leptoxis picta was not considered for listing.

We interrupt this extended history lesson for a brief spasm of science. I was sent large samples of all four of these nominal species (8 populations, 30 individuals per population) by our colleague Chuck Lydeard in 1996. The sample of L. picta I received was of larger, older, and more heavily-shelled animals (10), but otherwise no morphological difference between L. picta, L. ampla, and L. taeniata was apparent. My sample of Leptoxis plicata was distinctive by their higher-spired shells, bearing slight carination.

I did a proper allozyme study, comparing divergence at 9 loci among the 8 populations to 3 populations of Leptoxis praerosa, the common and well-characterized species widespread in Tennessee drainages to the north (11). The levels of genetic divergence among the picta, ampla, and taeniata populations were negligible. So it was quite clear, as of 1996, that all the Leptoxis populations known to have survived in the Alabama/Coosa River system were conspecific, L. picta being the oldest name for the group. Leptoxis plicata (of the Tombigbee/Black Warrior system) would appear to be a valid biological species.

So in summary, two of the three nominal species of Leptoxis currently on the US endangered species list are junior synonyms of a third species, which is not listed. What lessons can be learned from this mess?

Once again we see a vivid demonstration that science and public policy are two entirely different things. Most of you have heard me preach this sermon before, so I won't preach it again (12). Scientists have a language, culture, value system, and assumptions about the world that are completely different, no better or worse, from the language, culture, values, and assumptions brought by politicians, lawyers, and the natural resource managers who put laws into practice.

The adjective "endangered" is not scientific - it can't be measured, quantified, verified, or falsified. A designation of endangerment is the result of a political process, and by that process Leptoxis plicata (for example) is endangered and Leptoxis picta is not.

Now we read that yet another nominal species of Leptoxis from the Mobile Basin has been proposed for protection under the US Endangered Species Act (13). Field surveys undertaken in the upper Coosa in the late-1990s led to the discovery of a pleurocerid population in the Oostanaula River of North Georgia that has been identified as Leptoxis downei or L. foremani. In the last ten years, this population has become the target of an extensive recovery effort, our colleague Paul Johnson initiating a captive propagation program at the Tennessee Aquarium Research Institute in 2000, which he carried with him to the Alabama Aquatic Biology Center in 2005 (14).

But is Leptoxis foremani a valid biological species? Tryon synonymized foremani under L. picta in 1873, and the taxon was only resurrected by Goodrich in 1922 on the slenderest of threads (15). So given the tortured history of Leptoxis systematics in the Mobile Basin through 150 years, are we surprised that so much time, money and effort has been spent on conserving "L. foremani," while no effort whatsoever has apparently been directed toward establishing its biological reality? Nope. Science and public policy are two entirely different things.


(1) I'm going to fight the urge to digress into a discussion of the genus-level taxonomy here. Maybe one day soon. In the mean time, for the purpose of this essay, I'm lumping Anculosa and Nitocris/Mudalia together under Leptoxis.

(2) Tryon G. W. (1873) Land and Freshwater Shells of North America. Part IV, Strepomatidae. Smithsonian Miscellaneous Collections 253: 1 - 435.

(3) "The Legacy of Calvin Goodrich" See my Post of January '07.

(4) Goodrich, C. (1922) The Anculosae of the Alabama River Drainage. Misc. Publ. Univ. Mich Mus. Zool. 7: 1-57.

(5) The suviving taxa depicted on Goodrich's (1922) Plates I and II are as follows: Figs 3 - 5 are L. ampla, Figs 18-19 are L. foremani, Figs 34 - 35 are L. picta, Figs 36-38 are L. plicata, Figs 46 - 49 are L. taeniata.

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

(7) Here's another digression I hate to take. The Mobile Basin is composed of two halves - the Alabama/Coosa and the Tombigbee/Black Warrior. Most of the literature we are reviewing here is for subsets. Goodrich's (1944) "Pleuroceridae of the Coosa River Basin" would include just a geographical (not taxonomic) subset of his (1922) "Anculosae of the Alabama River," for example, and neither work would include populations like L. plicata of the Black Warrior. A map of the Mobile Basin is available [here].

(8) Goodrich, C. (1944) Pleuroceridae of the Coosa River basin. Nautilus 58: 40-8.

(9) Endangered status for three aquatic snails, and threatened status for three aquatic snails in the Mobile River Basin of Alabama. 63 FR 57610-57620 [PDF]

(10) Goodrich himself prominently noted the relationship between river size and pleurocerid shell morphology on many occasions. See my post of February '07, "Goodrichian Taxon Shift." We will return to this subject very soon.

(11) Dillon, R.T., and C. Lydeard (1998) Divergence among Mobile Basin populations of the pleurocerid snail genus, Leptoxis, estimated by allozyme electrophoresis. Malacologia 39: 111-119. [PDF]

(12) For example, "Idaho Springsnail Panel Report" (December '05), or "Red Flags, Water Resources, and Physa natricina." (March '08).

(13) Mobile Basin I: Two pleurocerids proposed for listing. Post of August '09.

(14) Interrupted Rocksnail Reintroduced to the Coosa River. Outdoor Alabama, February 2004, p. 33 [PDF]

(15) "In shell characters this species (L. foremani) is closer to A. picta Conrad than is A. formosa Lea. But while the operculum of picta and formosa are much alike, that of foremani is like the operculum of neither. The similarity of the shells of formosa and foremani, picta out of consideration, varies strangely with locality, the resemblances and differences seeming to play a game of see-saw as the collector travels down the Coosa River." (Goodrich 1922: 18).

Monday, August 24, 2009

Mobile Basin I: Two Pleurocerids Proposed for Listing

The fauna of the Mobile Basin has become a cause célèbre - perhaps the cause célèbre - of freshwater gastropod conservation in North America. I am aware of four general calls-to-arms issued in recent years that have focused on the plight of this famously diverse biota, inhabiting creeks and rivers through the length of Alabama, edging into East Mississippi and North Georgia (1). The review of Neves and his colleagues, for example, cataloged 118 freshwater gastropod species in the Mobile Basin in ten families, suggesting that as many as 38 may have been lost to extinction in the 20th century, with another 70 threatened. Yet only seven of the species remaining are currently protected under the US Endangered Species Act: four pleurocerids (Leptoxis ampla, L. plicata, L. taeniata, Goniobasis crenatella), two viviparids (Tulotoma magnifica and Lioplax cyclostomaformis) and one hydrobiid (Lepyrium showalteri).Now after a hiatus of over ten years, in late June the US Fish and Wildlife Service announced a proposal to list two new Mobile Basin pleurocerids: Leptoxis foremani and Pleurocera foremani (2). The comment period ends this Friday, August 28. Any of our colleagues on this list who might wish to offer "comments, suggestions, and any additional information on biology, threats, range, distribution, population size, or current or planned activities and the activities' possible impacts on these species or their proposed critical habitats" will find instructions on the FWS website [here].

But what do we actually know about the freshwater gastropods of the Mobile Basin? Their taxonomy almost entirely predates the Modern Synthesis. We have seen that Calvin Goodrich, for example, seemed to have second thoughts about the 26 species of Leptoxis he catalogued in 1922 (3), later coming around to the realization that much of the shell variation expressed in North American pleurocerids may be ecophenotypic in origin (4). A bit of digging into the 6/29 issue of the Federal Register that formally proposes the new pleurocerids for listing will reveal a reference to the recent dissertation of Jeffrey Sides, reporting negligible sequence difference between P. foremani and a co-occurring species of an entirely different genus, Goniobasis ("Elimia"). What gives?

This is the first in what will probably turn out to be a sporadic series of essays on the freshwater gastropod fauna of the Mobile Basin. Between the undeniably fascinating evolutionary biology of this unique fauna and the complications of politics, personalities, and public policy there are, no doubt, many lessons to be learned.


(1) Brown, K. M & P. D. Johnson (2004) Comparative conservation ecology of pleurocerid and pulmonate gastropods of the United States. Amer. Malac. Bull. 19: 57-62. Lydeard, C. et al. (2004) The global decline of nonmarine mollusks. BioScience 54: 321 - 330. Neves, R.J., A E. Bogan, J. D. Williams, S. A. Ahlstedt, and P. W. Hartfield (1997) Status of aquatic mollusks in the southeastern United States: A downward spiral of diversity. Chapter 3 in Aquatic Fauna in Peril: the Southeastern Perspective (Benz & Collins, eds.) Southeast Aquatic Research Institute Publication 1. Lydeard, C. & R. L. Mayden (1995) A diverse and endangered aquatic ecosystem of the southeast United States. Conservation Biology 9: 800-805.

(2) Service Proposes Endangered Species Status and Critical Habitat Designations for the Georgia Pigtoe Mussel, Interrupted Rocksnail, and Rough Hornsnail: http://www.fws.gov/southeast/news/2009/r09-035.html

(3) Goodrich, C. (1922) The Anculosae of the Alabama River drainage. Misc. Publ. Mus. Zool. Univ. Mich., 7, 1-57

(4) "The legacy of Calvin Goodrich." FWGNA post of January '07. "Goodrichian Taxon Shift." FWGNA post of February '07.

Tuesday, July 14, 2009

Megapetitions of the Old West

There's a new posse riding the plains, and they're aiming to make the American West safe for all its law-abiding citizens, including the malacological ones. And on their hips, they're toting sawed-off scatterguns.

The Center for Biological Diversity (CBD) is celebrating its twentieth anniversary this year. There's a beautifully-formatted booklet available for download from their web site packed full of dramatic tales such as "A bare-knuckled trio takes on Big Timber" and "Sprawl Showdown." With a main office in Tucson, and field offices in eight other states, their staff of 60 (including 17 lawyers) works "to secure a future for all species, great and small," with a "vision and a solar-powered fax machine.

"Their efforts thus far have been impressive. In recent years CBD gunslingers have prevailed in shootouts over Pyrgulopsis roswellensis, Juternia kosteri and Assiminea pecos in New Mexico, as well as P. morrisoni in Arizona. Their web site (accessed 10July09) catalogues 86 listing petitions, 5 critical habitat petitions, and 9 species status reviews along with scores of "research papers."

Recently the CBD posse seems to be dramatically expanding its efforts on behalf of our favorite creatures with a couple petitions along an unusual line of approach. Taking advantage of the 1994 FWS policy encouraging "Multi-species listings…when several species have common threats, habitat, distribution, landowners, or features that would group the species and provide more efficient listing and subsequent recovery,” in 2008 the CBD filed "Petition to list 32 mollusk species from freshwater and terrestrial ecosystems of the northwestern United States as Threatened or Endangered under the Endangered Species Act." [PDF, 2.0 MB] Then in February of this year they let loose with an even bigger blast, "Petition to list 42 species of Great Basin Springsnails from Nevada, Utah, and California as Threatened or Endangered under the Endangered Species Act." [PDF, 1.7 MB]

The 2008 volley, weighing in at 85 pages, proposed 17 freshwater snails of three familes for protection: 14 hydrobiids (11 Fluminicola, 3 "Lyogyrus"), 2 pleurocerids (Juga), and one planorbid (a Vorticifex), as well as 15 land snails of diverse groups. The taxonomy was a complete mess, and the document an embarrassment (1). The causes of three valid species (Fluminicola seminalis, F. potemicus, and Colligyrus convexus) were buried under the weight of 14 spurious taxa proposed in various unpublished reports by the late Terry Frest. I hope that the poor FWS biologist sitting behind the desk on which this dead coon is currently stinking can find it in his heart to forgive us.

So the 2009 petition, tipping the scales at 133 pages, could only be better. The 42 hydrobiid species it proposes for protection include 37 Pyrgulopsis and 5 Tryonia, all endemic to single springs or sets of springs in Nevada or closely adjoining regions (For example, the spring at Point of Rocks figured above, in the Ash Meadows National Wildlife Refuge, NV). All 42 species have been recently monographed by (in fact, mostly described by) Bob Hershler (2). I don't have any personal experience in this part of the world, but from my seat on the corral fence, if these diminutive citizens of the Old West don't need a bit of protection, I don't know who does.

The advantage of a megapetition approach ought to be in speed and efficiency. The 2009 petition features just one (collected) section entitled "Natural History and Ecology" for the entire list of 42 species, and I think this is justifiable. Treating all these populations together where possible ought to yield substantial savings in time and manpower for the CBD to research, and the FWS to process - savings which should translate into quicker results.

But on the downside, weakness in any element of a megapetition may translate to the whole. It's hard to sell a bag of 17 apples and 15 oranges, when 14 of the apples are rotten.

Both the 2008 and 2009 petitions called the attention of the Secretary of the Interior to laws "placing definite response requirements on the FWS and very specific time constraints on those responses." Apparently federal regulations require that the FWS respond to petitions such as these in 90 days. Well, I don't think anybody actually expected that to happen. The FWS simply does not have the staff or the expertise to evaluate documents of this heft at time scales marked in days. I understand that it generally requires a minimum of 15 months to obtain a 90-day finding, 15 months being the earliest point at which a "timeline suit" can be filed.

So it looks like our little snails will be holding off the development desperados by themselves a little bit longer. In the meantime, we'll keep an ear to the rail, and an eye toward the sunset.


(1) I am not criticizing the CBD here. Their proposal can only be as strong as the science on which it is based.

(2) Hershler, R. & D.W. Sada (1987) Springsnails (Gastropoda: Hydrobiidae) of Ash Meadows, Amargosa Basin, California-Nevada. Proc. Biol. Soc. Wash. 100: 776-873. Hershler, R. (1994) A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Smithsonian Contrib. Zoology 554: 115 p. Hershler, R. (1998) A systematic review of the hydrobiid snails (Gastropoda: Rissooidea) of the Great Basin, Western United States. Part I. Genus Pyrgulopsis. Veliger 41: 1-132.

Wednesday, June 10, 2009

Just One Species of Ferrissia

Editor's Note:  A substantial fraction of the material in this essay was subsequently rendered obsolete by the 2010 research of Walther and colleagues.  See my post of [8Dec10] for more.

I'm pleased to report the publication of a paper by J. J. Herman and myself in this month's Journal of Freshwater Ecology, "Genetics, shell morphology, and life history of the freshwater pulmonate limpets Ferrissia rivularis and Ferrissia fragilis (1)." In this work we offer evidence that populations of the two most widespread limpets in North America reproduce entirely by self fertilization, and that the shell morphological criteria by which they have been distinguished are the result of ecophenotypic plasticity. We suggest that the nomen Ferrissia fragilis is a junior synonym of F. rivularis.

The modern taxonomic history of the North American Ancylidae has been one of consolidation (2). Basch (3) recognized five species of Ferrissia (rivularis, fragilis, parallela, walkeri and mcneilli), noting as he did that "ecological phenotypes are numerous, and plasticity of shell form has been remarked upon many times." (See Basch's charming figure above). More recently Andrea Walther's sequence data have suggested just two Ferrissia lineages, which she has correlated with the rivularis and fragilis phenotypes and life habits (4).

But our discovery of asexual reproduction voids the biological species concept, and necessitates a retreat to the morphological. And since there seems to be no heritable component to the shell characters conventionally used to distinguish rivularis and fragilis (see figure below), it would appear that a single-species model fits the situation best.

I gather that Andrea and her advisor Dairmaid O'Foighil prefer to retain the two species model, under one of the many species concepts based on gene trees. But the limitations of the various phylogenetic and cladistic species concepts are well known (5).

The situation with Ferrissia in North America seems biologically analogous to that of the better-studied Ancylus fluviatilis in Europe. A phenotypically plastic response of shell height and shell thickness to current and substrate has been well known in A. fluviatilis populations for years, and Städler and colleagues (6) documented asexual reproduction in the mid-1990s. More recently Pfenninger and colleagues (7) have reported that 103 populations of A. fluviatilis sampled from across Europe can be grouped into four DNA clades. Yet European workers seem content to identify all their limpet populations by the same nomen, Ancylus fluviatilis.

If there were a reliable correlation between Andrea's gene trees and any criterion by which rivularis and fragilis have been distinguished in the past, an argument could be made for retaining both nomina as labels for asexual lineages. But Andrea misclassified the samples we sent her in 2007 from our North Saluda River population as F. fragilis, even though they were collected from a rocky stream and bore robust, acutely conical shells. One species of Ferrissia it would seem to be.


(1) Dillon, R. T., Jr. & J. J. Herman (2009) J. Freshw. Ecol. 24: 261-272. [PDF]

(2) See the FWGNA archives of July '07, "Phylogenetic sporting" in the genus Laevapex.

(3) Basch, P.F., 1963. A review of the recent freshwater limpet snails of North America (Mollusca: Pulmonata). Bull. Mus. Comp. Zool. Harvard Univ. 129: 399–461.

(4) Although I have seen some data from Andrea's recent Ph.D. dissertation at the University of Michigan, I have not seen the work itself. This is from my personal communication with Andrea and her advisor, together with the abstracts of talks she has given in recent years.

(5) See the FWGNA archives of July '08: Gene trees and species trees.

(6) Städler, T., M. Loew and B. Streit. 1993. Genetic evidence for low outcrossing rates in polyploid freshwater snails (Ancylus fluviatilis). Proc. R. Soc. Lond. B 251: 207-213. Städler, T., S. Weisner and B. Streit. 1995. Outcrossing rates and correlated matings in a predominantly selfing freshwater snail. Proc. R. Soc. Lond. B 262: 119-125.

(7) Pfenninger, M., S. Staubach, C. Albrecht, B. Streit and K. Schwenk. 2003. Ecological and morphological differentiation among cryptic evolutionary lineages of freshwater limpets of the nominal form-group Ancylus fluviatilis (O. F. Muller, 1774). Molecular Ecology 12: 2731-2745.

Tuesday, May 26, 2009

Freshwater Gastropod Databases Go Global!

Last month we reviewed the not-insubstantial progress that many of our larger national and regional research museums have made with electronic data capture, evaluating their on-line holdings of North American freshwater snails. Among the many nice comments I received from that post were several calling my attention to the Global Biodiversity Information Facility, a remarkable data network hosted in Copenhagen. Some of our colleagues feel strongly that the GBIF “Portal” represents the future of online museum databases worldwide.

The system is administered by a governing board, 30 participating countries, and 20 associate countries. It hosts (as of 26May09) over 174 million records across the diversity of eukaryotic life, contributed by 289 data providers worldwide. My query for “Campeloma” entered into the single, simple search box returned an impressive 3,210 records, as follows:

1,414 Florida Museum of Natural History
852 Academy of Natural Sciences, Philadelphia
498 North Carolina State Museum
145 University of Colorado Museum
127 US National Museum
55 Yale (Peabody) Museum
116 (Nine other institutions)

The FLMNH, ANSP, and USNM numbers are reassuringly close to the figures I obtained from my queries to their local on-line datbases, as reported last month. I didn’t think to look at the NCSM last month (Shame on me!) but the (rather impressive) 498 records I retrieved from the GBIF also closely approximate the results I would have gotten from a query to their local site, had I visited. I also didn’t think to look at the Peabody Museum last month, but in this case, the 55 records available from the GBIF are significantly improved over the 15 I would have come away with from a visit to their local on-line database. And the University of Colorado Museum records are a bonus – the UCM no longer maintains a local site, so it’s Copenhagen or nothing. The power of the GBIF idea is undeniable.

The GBIF portal features a gee-whiz mapping function for your results, which plots the occurrence of your taxon of interest on one-degree cells, with the capability of zooming to 0.1 degree and exploring. It also offers the option of exporting search results in several vanilla types of file formats, which you can download, sort and subsample to your heart's content.

So I've added a link to the Global Biodiversity Information Facility from the FWGNA information resources page, and I expect to be hitting that link with increased frequency in the coming years.

Wednesday, April 15, 2009

Progress in the Museums

To the FWGNA group:

It's been several years since we last took an electronic tour around the major systematic collections of North American freshwater mollusks. And it's nice to see such good progress being made in on-line database access. When the FWGNA project kicked off in 1998, only two national or regional collections of freshwater gastropods were effectively searchable on line: The Florida Museum and the ANSP. Today that small club has been joined by eight other museums. I'm impressed!

Databasing efforts are, of course, an ongoing project in all active systematic collections. But I thought it might be useful for our group if I took a snapshot of the distributional information available on-line for North American freshwater gastropods, as of April 2009. Developing an independent metric by which to evaluate and compare ten disparate databases was, however, something of a challenge.

My first thought was to query each database for all records of a common and widespread freshwater gastropod family, such as the Physidae. But alas, many of the ten databases are not searchable by family - only by genus or species. And most of the lower taxa are regional in their distributions and taxonomically unstable - not the best targets for a comparative search.

After some head-scratching, I've decided to evaluate the ten on-line databases by the number of Campeloma records currently retrievable. Campeloma is the most widespread and stable genus of North American freshwater gastropods I can think of, although its distribution does introduce a bias against museums with predominantly western holdings. The California Academy of Sciences ranks #8 by Campeloma, but would certainly rank above the Field Museum (#6) by physid records, if all the collections were rankable using that criterion. But for what it's worth:

(1) University of Michigan Museum of Zoology
Campeloma = 2,456
Searchable by Family = No

(2) Florida Museum of Natural History
Campeloma = 1,414
Searchable by Family = Yes (Physidae = 2,063)

(3) Academy of Natural Sciences, Philadelphia
Campeloma = 890
Searchable by Family = Not effectively

(4) Museum of Comparative Zoology, Harvard
Campeloma = 488
Searchable by Family = Yes (Physidae = 1,033)

(5) National Museum of Natural History, Smithsonian
Campeloma = 127
Searchable by Family = Yes (Physidae = 793)

(6) Field Museum of Natural History
Campeloma = 88
Searchable by Family = Yes (Physidae = 149)

(7) Illinois Natural History Survey
Campeloma = 62
Searchable by Family = No

(8) California Academy of Sciences
Campeloma = 2
Searchable by Family = Yes (Physidae = 290)

(9) Los Angeles County Museum
Campeloma = 1
Searchable by Family = Yes (Physidae = 3)

(10) Bailey-Matthews Shell Museum
Campeloma = 1
Searchable by Family = Yes (Physidae = 0)

All of these on-line databases, I'm pleased to report, are searchable by double criteria, such as species AND state/province. Two databases were able to handle my (rather complicated) "Physa OR Physella" query, by which I was trying to eliminate the double-counting of records where Physella is a subgenus but not a genus: MCZ and LACM.

Kudos to all our hard-working colleagues in the ten museums listed above! And for our colleagues working at the museums listed below - a word of encouragement. I know funding is tight, but we're all in this together. So hang in there, get those grants, we're rooting for you!

Other Museums visited, Collections not on line at present:
American Museum of Natural History
Canadian Museum of Nature
Carnegie Museum (Pittsburgh)
Delaware Museum of Natural History
Ohio State Museum

And keep in touch, everybody!

Monday, March 16, 2009

The Snails The Dinosaurs Saw

I imagine most of us are familiar, at least in passing, with the North American Benthological Society ("NABS"), and their excellent journal, J-NABS (1). Published quarterly since 1982, J-NABS has built a solid reputation as an outlet for peer-reviewed research on any aspect of the biota "on the surface of the bottom" of lakes and rivers worldwide. The journal has rarely, however, been seen as a vehicle for anything edgy.

Perhaps in response to that perception, in 1998 a wealthy benefactor endowed the Rosemary Mackay Fund to support the publication of "speculative, forward-thinking, and philosophical" research in J-NABS. There have been four Rosemary Mackie Awards in the last ten years (2).

I am here pleased to announce that a paper by John Robinson and myself has been selected as the fifth winner of this prestigious award. Our work, entitled "The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?" leads off this month's issue of J-NABS. A download of the full article is available here [PDF].

One of the perks that accompanies a Rosemary Mackie Award is that the winning paper (and its authors) are featured in the NABS newsletter, In the Drift. This "Article Spotlight" feature for "The Snails The Dinosaurs Saw" is reprinted below (3). I apologize if the tone seems a bit self-indulgent - this seems to be what the editor was asking for.

This is, in any case, as edgy as freshwater snail research gets.
Read on if you dare!

JNABS Article Spotlight: Snails the Dinosaurs Saw

My grandmother once observed, “Robbie Tom sure do love to play in the crick.” This remark she made to my father, as they sat rocking on her front porch at the foot of the Blue Ridge in Patrick County, Virginia. I would have been about 25 years old at the time, sampling Goniobasis proxima from the stream in her back yard for my dissertation research (above).

In one sense, the research project yielding the results that John Robinson and I reported in our "dinosaur" paper would never have been initiated without the Rosemary Mackay Fund. Our hypothesis that a large group of obscure freshwater snails evolved on the west side of the towering ancient Appalachians hundreds of millions of years ago, and then rode the mountains down as they eroded almost to base level, without moving or even noticeably evolving, is simply too wild to publish as conventional science. But in a second, broader sense, I've been working on this project for 40 years.

Because my grandmother was right. For as long as I can remember, I have been playing in the rivers and streams of the southern Appalachians, where the most conspicuous element of the macrobenthos is the pleurocerid snails. Through my childhood in the Shenandoah Valley it was Leptoxis carinata, in the upper New River where I did my undergraduate research it was Goniobasis proxima, and through the piedmont of the Carolinas it was Goniobasis catenaria.

Common sense suggests that these populations must be ancient. The snails have such limited dispersal capabilities that significant gene frequency differences can develop across a three-meter corrugated metal culvert. Yet Goniobasis proxima populations are common in almost every little creek draining both sides of the Appalachian divide from southern Virginia to north Georgia. How could bird dispersal account for such a range?

So perhaps my colleague, Bob Frankis, and I should not have been surprised by the first DNA sequence data we obtained for three populations of G. proxima in the summer of 2000. We found tremendous genetic diversity both between and within populations – up to 16.9% sequence divergence between two G. proxima individuals collected from the same rock in a Dan River tributary from the Virginia Piedmont. To us, these results suggested both that our pleurocerid populations must be ancient, and that natural selection might have acted to distribute gene frequencies across a pair of quite distant adaptive peaks.

But to journal reviewers, such results could only mean one thing – cryptic speciation. My 20 years of data demonstrating random mating within local populations of G. proxima, and no evidence of reproductive isolation between them, carried no weight with most of my immediate colleagues. In the community of phylogenetic systematics, the biological species concept has been replaced by a variety of typological concepts that discount reproductive relationships. The little paper that Bob and I wrote was rejected by four journals, before I finally managed to get the thing published in an issue of the American Malacological Bulletin that I myself guest-edited in 2004. I vowed never again.
But in 2006 I read Pam Silver’s editorial in J-NABS, renewing the call for “speculative, forward-looking, and philosophical” articles to publish through the Rosemary Mackie Fund. And I was also fortunate to have John Robinson in my lab at the time (left). John came to Charleston as an M.S. student in Marine Biology, but was always eager for good research conducted in any environment, and blessed with molecular skills far superior to my own. So together we developed a sampling design to extend the results of Dillon & Frankis across 13 populations of three pleurocerid species, and over the eastern continental divide.

Such a project could never win external funding. The mainline systematic community is heavily invested in "Assembling the Tree of Life” using techniques dependent on an assumption of neutrality. Our hypothesis of multiple adaptive peaks in ancient and polymorphic populations is genuinely subversive to such a project. If true, it would imply that “The Tree of Life” can no better be reconstructed with molecules in the 21st century than it was with morphology in the 19th.

So oddly enough, the project overcame its final hurdle when John graduated and moved up to the University of Georgia. His Ph.D. adviser, John Wares, was both supportive and indulgent when a few samples of our freshwater snails slipped into the queue for his sequencer. Our special thanks go to Dr. Wares, as well as to the RMF Committee, for making this research possible.

The hypothesis we are advocating yields quite a few surprising predictions. In addition to challenging the basic assumptions of molecular phylogenetics, our model will upset most geomorphologists, who today think it unlikely that the eastern continental divide has migrated, and most malacologists, who postulate independent origins for American and African cerithiacean snails, and cryptic species in every creek.

But setting aside the craziness, John and I hope that our paper brings forward some assumptions that all we benthologists probably carry in the back of our minds, but may not examine as often as we should. Many elements of the freshwater biota are much older than those of the terrestrial environments surrounding them. All those ancient orders of aquatic insects, for example, probably evolved long before the seed plants that provide most of the primary productivity for the rivers they inhabit today. Standing at creek side, looking down, we look back millions of years. Even if our snails didn't see dinosaurs, that's an important thing to keep in mind.


(1) There's still time to register for the NABS annual meeting, scheduled for May 17 - 22 in Grand Rapids! Once again I've volunteered to man the Gastropoda booth at the "Taxonomy Fair" on the afternoon of the 19th. Come by to see me!

(2) The third in the series was by our colleague Dave Strayer (2006), Challenges for freshwater invertebrate conservation. JNABS 25: 271-287.

(3) The actual article, as it appeared on Page 2 of the Winter 2009 In The Drift, was shortened a bit for publication, and had several additional photos. [PDF]

Wednesday, February 25, 2009

Charles Darwin, Freshwater Malacologist

Editor's Note - Shortly after I posted this email, our good friend Aydin Orstan contacted me with a suggestion that we might add Darwin's research with land snails and collaborate on a larger paper.  This was ultimately published as Orstan & Dillon (2009) Charles Darwin the Malacologist. Mollusc World 20: 4 - 6 [PDF].

Charles Darwin, whose 200th birthday the world has just celebrated, may have been the last complete biologist. His research interests spanned the entirety of the life sciences as they were known in his day, from his "Monograph on the Subclass Cirripedia" (1851) through his "Descent of Man" (1871) to "The Power of Movement in Plants" (1880). Darwin’s first publication (1839) was a ripping-good adventure story featuring "atmo-spheric dust with infusoria (1)." And his last publication, a four-paragraph communication appearing in 1882 just two weeks before his death, was a work of freshwater malacology (2).

In fact, Darwin first touched on freshwater mollusks in his (1859) "Origin of Species." Early in the chapter he entitled "Geographical Distribution – Continued," Darwin observed, "Some species of fresh-water shells have very wide ranges, and allied species which, on our theory, are descended from a common parent, and must have proceeded from a single source, prevail throughout the world. Their distribution at first perplexed me much." But Darwin then went on to relay a number of anecdotes regarding the attachment of juvenile freshwater mollusks to the feet and feathers of waterfowl, concluding his lengthy paragraph with "Sir Charles Lyell informs me that a Dytiscus (3) has been caught with an Ancylus firmly adhering to it."

Darwin’s fascination with dispersal and biogeography brought him back to the subject of freshwater malacology again in 1878 (4), with a charming anecdote about a surprisingly large unionid mussel found attached to the toe of a duck shot in Danversport, Massachusetts (figure at left). And it reached full flower in 1882, with his "On the Dispersal of Freshwater Bivalves (5)."

Darwin opened this, the last paper he would publish before his death, with "The wide distribution of the same species, and of closely-allied species of freshwater shells must have surprised every one who has attended to this subject." After reviewing his observations of 1859 and 1878, Darwin wrote, "I am now able to add, through the kindness of Mr. W. D. Crick, of Northampton, another and different case. On February 18 of the present year, he caught a female Dytiscus marginalis, with a shell of Cyclas cornea (6) clinging to the tarsus of its middle leg." Darwin went on to relay additional data about this now most illustrious of all fingernail clams, which was large (0.45 inch), viable (dropping from the bug only after five days) and fertile (bearing two juveniles). He then added several anecdotes about other individual sphaeriids found attached to the digits of amphibians, and finished with the charming observation that "my son Francis, while fishing in the sea off the shores of North Wales, noticed that mussels were several times brought up by the point of the hook."

Darwin concluded his 1882 work, "there can, I think, be no doubt that living bivalve shells must often be carried from pond to pond, and by the aid of birds occasionally even to great distances." This point may seem a bit trivial to us today, perhaps even quaint (7). But Darwin’s central thesis, that all these creatures have diverged from a single common ancestor, required that they have originated at a single point, and dispersed throughout the world. If a convincing case could be built for freshwater mollusks, surely to be ranked among the most disadvantaged of the world’s dispersers, perhaps the remainder of the worldwide biota might fall into line.

There’s an interesting postscript to the story of Charles Darwin’s career as a freshwater malacologist. The "Mr. W. D. Crick of Northampton" who sent Darwin his report of the fingernail clam pinched on the water bug leg was Walter Drawbridge Crick (1857-1903), the grandfather of Francis H. C. Crick, who (with James Watson & Maurice Wilkins) shared the 1962 Nobel Prize for elucidating the structure of DNA (8).

At the outset of this essay, I characterized Charles Darwin as “the last complete biologist.” Chief among the reasons that there can be no more such protean figures must be the 20th century explosion of molecular biology, which has expanded our discipline in directions Darwin could never have imagined. It is a source of some inspiration to me that one can trace a path from Darwin to DNA through the great man’s last paper, and the humble discipline of freshwater malacology.


(1) Yes, Chapter 1 of Darwin’s “Voyage of the Beagle” included a passing note about “infusoria” (primarily diatom frustules) in dust accumulated while on shipboard.

(2) I’ve taken a bit of license with this paragraph. Darwin had a couple publishing credits prior to his (1839) “Voyage,” and several posthumous papers after his 6 April 1882 paper on freshwater bivalve dispersal. Darwin’s complete bibliography, including PDF downloads of the papers mentioned here, is available at Darwin Online.

(3) Dytiscus is a genus of large, predatory water bugs. Although spending the great majority of their lives swimming gracefully through the water column, they may on occasion take to the wing, flying like balsa-wood airplanes with old rubber bands.

(4) Darwin, C. (1878) Transplantation of shells. Nature 18: 120-121.

(5) Darwin, C. (1882) On the dispersal of freshwater bivalves. Nature 25:529-530.

(6) The genus Cyclas has since been synonymized under Sphaerium. Today this common European "fingernail clam" is generally referred to as Sphaerium corneum.
(7) It is not, however. See the classic paper:W. J. Rees (1965) The Aerial Dispersal of Mollusca, Proc. Malac. Soc. London 36: 269 - 282.

(8) We must acknowledge an article in the February 2009 issue of National Geographic for calling our attention to this remarkable coincidence: Ridley, M. (2009) Modern Darwins. National Geographic 215: 56 - 73.