The Western Pyrgulopsis: 151 planets in the sky?

I love retirement for many reasons, not the least of which is that it is a good excuse.  I very rarely submit grant proposals or papers to scientific journals anymore, and so very rarely volunteer to review anybody else’s.  I do not attend meetings because – you know – fixed income!  And as for serving on committees, boards, and panels, I have paid my dues.

Pyrgulopsis neritella (A,B) and landyei (C-F). From [1]

But on 28Sept26 I received a courteous email from a Dr. Jacob Burkhart from the US Fish & Wildlife Service, Midwest Regional Office, out in Minnesota somewhere, I think.  He explained that he was working on a team that is completing a “Species Status Assessment for several Pyrgulopsis springsnail species found in the Steptoe Valley of Nevada,” and asked me if I “would be willing to provide a peer review” of their “proposed treatment of springsnail taxonomy.”  And my rusty old armor cracked open just a bit.  His situation was just so pathetic.

So here is my reply, verbatim:

“Well, OK.  One of my favorite quotes in the history of the world comes from Dr. Seuss’ Cat in the Hat: ‘This mess is so big, and so deep and so tall, We cannot pick it up. There is no way at all.’ But I suppose it is my duty to help you try.”

So on 2Oct26 my new friend Jacob sent me a 6-page document entitled “NV Springsnails Taxonomy Summary For Peer Review."  In this document he and two FWS colleagues briefly reviewed their motivation, which turned out to be rooted in that “Megapetition” from the Center for Biological Diversity we reviewed way back in [14July09], see also [18May11].  Jacob and colleagues then soldiered bravely through thirty years of scattered, disorganized, ambiguous, confusing and contradictory gobbledygook, ultimately resolving to “evaluate the following entities for the purposes of this SSA report: P. landyei, P. neritella, P. sulcata, P. sterilis, and P. CS28.”  Bless their hearts.

 

And along with his little document for review, Jacob attached a huge bolus of supporting materials, including an important paper by Mike Young and five colleagues [2] that I will confess to you right now, I had been cravenly avoiding.

 

In early August I had received a comment from Mike at the bottom of my [7Sept22] post to this blog, “Just 125 of Pyrgulopsis in the American West.”  See note [3] about my species count.  I had prophesied that “One day, I feel sure, somebody will come behind (Bob Hershler) and test the 125 (Pyrgulopsis species) that remain.”  And I had concluded “I cannot imagine when, or by whom.  Not it.”

 

In August, Mike Young had answered, “We did it. And it appeared yesterday in Western North American Naturalist.”  To that comment I responded, “Great news! Could you send me a pdf?”  Alas, his answer turned out to be no.  And my effort to download a copy for myself was defeated by a paywall.

 

One of the very few things I do not love about retirement is that I have lost my access to most of the scientific literature being published today.  Sure, I could impose on colleagues in higher education to download a pdf for me, and occasionally I do.  Or, I could kick the Pyrgulopsis can down the road, and pray that the Son of Man might Return in all His Glory before I ever saw it again.

P. neritella (1.3 mm), P. landyei (1.4 mm). From [1]

Mike Young had been most cooperative when I reviewed his 2021 paper on Physa [5] back in 2024, and I knew him to be a hard worker, with excellent technical skills.  I had been impressed both by the quality and the quantity of the data he had gathered for that research effort, especially by the rigor with which he documented every nucleotide in every sequence, and every point to the right of the decimal in every sample site.  He was breathtakingly naïve regarding the biology of his study organisms, and pristinely ignorant of the published literature.  Consequently, he was utterly unable to state an hypothesis, much less test one.  But I was, and in his gigantic dataset I discovered a light sprinkling of rare cases bearing directly on the point of important hypotheses.

 

It was a lot of work to mine the diamonds from Mike Young’s mountain of slag, however, and I just was not sure I heard the call to do it again.  The Pyrgulopsis mess is today an order of magnitude worse than the Physa mess was at the dawning of my career, and going in the wrong direction.  Burch’s 1980 Bible [6] listed 16 species of Pyrgulopsis/Fontelicella in North America, and 65 species and subspecies of Physa.  Today we [7] count seven good, biological species of Physa [8], and 151 species of Pyrgulopsis.

 

Don’t get me wrong.  Science is the construction of testable hypotheses about the natural world.  To the extent that our current hypothesis about the western Pyrgulopsis is testable, it is science.  It is the intellectual equivalent of looking into the heavens and describing 151 planets, wandering randomly across the night sky [9].

 

Now here was Mike Young’s Pyrgulopsis paper open before me, with all 13 of his supplements in a zipped folder beside, and no sound of the trump, and I was clean out of excuses.  So, I dove in.  And I have never, in a professional career spanning over 50 years, laid eyes upon a more splendid dataset, a more cringeworthy analysis, or a more amazing result in the long and glorious history of freshwater gastropod population genetics [10].

 

First, the splendid dataset.  Mike and his colleagues sampled 4,270 individual Pyrgulopsis from 644 locations.  All were sequenced for the mitochondrial COI gene.  And “from each COI clade exhibiting a marked level of divergence and represented by more than one individual” Mike Smith sequenced one or more of three additional genes, mitochondrial ND1, nuclear ITS2 and nuclear 28S. 

 

To these 4,270 lines of data Mike and colleagues added 1,362 Pyrgulopsis sequences previously published, mostly of COI but a smattering of others.  And his entire 5,632-line [11], 22-column data set he made available as an excel spreadsheet in his Supplementary Material 2.  Splendid.

The 644 sample sites of Young et al. [2]

Regarding Mike Young’s analysis, it was, in two words, baroquely arbitrary.  Young characterized his species concept as “phylogenetic… requiring reciprocal monophyly” while specifying “an additional requirement for species-level rather than population-level divergence,” which is so obviously circular one wonders how such reasoning could be entertained in Western thought.  The application of this concept turned out to require such mental gymnastics such as: 

“Requiring reciprocal monophyly for the P. pilsbryana species complex would have resulted in recognizing all specimens as members of the type species, despite many populations exhibiting levels of divergence that were characteristic of valid species among other members of this genus.”

And how, one might wonder, did Mike Young determine that ‘characteristic’ level of species divergence, which seems to have been violated in what he decided a priori must be a P. pilsbryana “complex?”

The best way to summarize Mike Young’s baroquely-arbitrary analysis is to look back from a sample of his results.  The figure below is a tiny slice off the top of Young’s Figure 2, which is intended to relay the results for his Pyrgulopsis pilsbryana “species complex.”  At left is the maximum-likelihood COI tree showing six clusters.  The seven rows of boxes at right relay the results of his “identification of candidate species.”  This little subset of seven nominal species includes four previously-described (bedfordensis, blainica, ignota, and fresti), the daggers by ignota and fresti indicating that they are “not considered part of the pilsbryana complex,” apparently interlopers from some other “complex” unspecified.  There are also two candidate species as yet undescribed (CS21 and CS22), and one “informal group” sampled from Brush Creek “not assigned to a candidate species.”

I do not know how the six COI clusters at left map onto the seven candidate species at right.  Has the “informal group” from Brush Creek been subtracted from the gene tree?  We’ll let that go and soldier on.

Young et al. [2] Figure 2, detail.

Each of the seven rows has 11 columns, each column corresponding to one “species delimitation method.”  For a key to the 11 such methods, see Young’s complete Figure 2 caption at footnote [12].  Orange boxes indicate that this particular COI clade was delimited as a species, gray means no, white means no data, and an asterisk indicates “more than one taxon within the clade.”

 

And the main result I would like to highlight is this.  Six of the seven “candidate species” shown in this tiny slice off the top of Young’s results were in fact subsequently listed in his Table 1 as “valid,” all but that "informal group" from Brush Creek.  This despite the fact that no data were available for anything other than COI sequence for bedfordensis, blainica, fresti, or the as-yet-unnamed CS21 whatsoever.

 

Mike Young’s baroquely-arbitrary classification system ultimately devolved to ad hoc binning on the basis of one, single character.  On COI sequence alone [13], he and his colleagues ultimately listed 21 Pyrgulopsis species as “candidates for synonymy” and identified 17 “previously unrecognized clades” that “were delimited as candidate species,” for a net decrement of 4 species.  Our 151-planet hypothesis is now a 147-planet hypothesis.

 

I belong to an elite generation of evolutionary biologists who are old enough to have been influenced by Sneath & Sokal's numerical taxonomy [15], but not so old as to have forgotten it.  And vividly I remember how systematic biologists of that age used to rage against “single character classifications.”  Even given a genetic basis for the character being analyzed, it was universally understood fifty years ago that populations are the unit of evolution, and universally appreciated that populations demonstrate genetic variation both within and among, and with but a single character any interspecific variance that might be attributable to reproductive isolation cannot be recognized.

 

Note that I said above, “To the extent that our current hypothesis about the western Pyrgulopsis is testable, it is science.”  The bottom line is that Mike Smith’s cringeworthy analysis does not constitute a test.

But stepping back from the species hypothesis entirely, and simply understanding a COI sequence as the single genetic marker that it is.   We have now arrived at Mike Young’s amazing result, and the grand finale of the present essay.  Quoting him verbatim: 

“And given the fairly frequent co-occurrence of taxa—at 100 of the 1101 sites in this study, which is a minimum estimate—more thorough collecting and analysis of specimens from single sites is also warranted.”

Holy crap, could that be true?  The model of the Western Pyrgulopsis I have always borne in my mind has been one of complete allopatry.  One single nominal species per spring, never any more, right?  But returning to Mike’s big Supplement #2 spreadsheet, sorting by Location and running an eager finger down the first 1,000 rows or so, I counted six sample sites at which more than a single COI haplotype was discovered.  Wow.  That is quite simply, and quite profoundly, amazing.

 

Mike labeled each COI haplotype as a different “delimited species.”  And in so doing, he unwittingly committed an act of science.  He constructed an hypothesis about the natural world that can actually be tested.  Next month, we test it.

 

Notes:

 

[1] Hershler, R. (1998) A systematic review of the hydrobiid snails (Gastropoda: Rissooidea) of the Great Basin, western United States. Part I. Genus Pyrgulopsis. The Veliger 41: 1-132.

 

[2] Young, Michael K.; Pilgrim, Kristine L.; Miskow, Eric S.; Lundskog, Chante L.; Perez, Kathryn E.; and Schwartz, Michael K. (2026) "Molecular refinement of the taxonomy of Pyrgulopsis springsnails in western North America," Western North American Naturalist: Vol. 86: No. 2, Article 10.  Available at: https://scholarsarchive.byu.edu/wnan/vol86/iss2/10

 

[3] In my Bob Hershler essay of [6July22] I counted N = 126 species of Pyrgulopsis in the American West by paging through his (2017) “Annotated Checklist” [4].  Apparently molluscabase.org lists N = 151.  I have no insight to offer regarding the origin of this discrepancy.

 

[4] Hershler & Liu (2017) Annotated Checklist of Freshwater Truncatelloidean Gastropods of the Western United States, with an Illustrated Key to the Genera.  US Bureau of Land Management Technical Note 449: 1 – 142.

 

[5] Young, M.K., R. Smith K.L. Pilgrim, and M.K. Schwartz (2021) Molecular species delimitation refines the taxonomy of native and nonnative physinine snails in North America.  Scientific Reports 11: 21739. https://doi.org/10.1038/s41598-021-01197-3.  For my review, see:

• The SRALP and the SRNLP: A new hope [14May24]
• The SRALP and the SRNLP: Physa acuta were found [11June24]
• The twelve phascinating Physa of Bliss [2July24]
• Cytoplasmic male sterility in the Snake River Physa [7Aug24]

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

 

[7] The clarity brought to the Physa of North America is in large part due to the many years of laboratory and field effort logged by myself and my students, the likes of which I could never hope to match with Pyrgulopsis in what remains of my sojourn in this World of Woe.  It is true that a smattering of samples have passed across my lab bench in recent years.  But I must confess, I have never seen a Pyrgulopsis on the hoof.  So, let’s give that jumbo 28-oz can of Bush’s Baked Pyrgulopsis another swift kick, okay? No?

 

[8] The confirmed species of Physa in North America are: acuta, carolinae, gyrina, jennessi, pomilia, vernalis, and zionis.  One might also count Aplexa elongata as number 8. The jury is still out on ancillaria/parkeri. 

 

[9] Without the entry of a single new datum into evidence, Galileo and every other astronomer peering into the night sky of the seventeenth century immediately discarded Ptolomy’s geocentric model of the heavens and embraced Copernicus’ heliocentric model.  Two reasons.  First, the heliocentric theory is powerful, yielding strong predictions about the behavior of planets as yet undiscovered and capable of rejecting planets that cannot exist.  And second, the heliocentric theory is elegant.  I do not understand what has happened to our profession in these latter generations, but I do know this.  Most of the faculty in the university science departments and research institutes of today would not know a theory – elegant, ugly or otherwise – if it bit them on the bottom.

 

[10] Mike Young’s discovery of significant sympatry in the western Pyrgulopis fauna scored 94.1 international amazingness units, edging out the 93.2 iau scored by Bianchi and colleagues back in 1994.  For a complete ranking of the top five, see:

• The third-most amazing research results ever published for the genetics of a freshwater gastropod population [1].  And the fourth-most amazing, too. [3Mar22]

[11] The excel spreadsheet downloadable as Supplementary Material 2 does indeed contain 5,632 lines, but only 5,631 are data, line #1 being the column labels.  Apparently the gene sequence(s) from one individual Pyrgulopsis have been lost, for an error rate of 0.018%

 

[12] The complete caption of Figure 2, from [2]:  "Identification of candidate species for most members of the Pyrgulopsis pilsbryana species complex, structured following highly supported clades (branches with red dots and all collapsed nodes have bootstrap support >85) from the maximum-likelihood tree for the COI gene fragment. Taxa in bold are hypothesized candidate species; those marked with a dagger are not considered part of this complex (see text). Each column depicts the results of 1 species delimitation method (A, ASAP; P, Poisson tree processes; S, statistical parsimony networks) for mitochondrial data (COI, ND1, or the concatenated sequences [CON]) or diagnosability (D) and substantial molecular support (B, bootstrap support ≥85) for nuclear data (ITS2 or 28S). Cell fill denotes whether a COI clade was delimited as a species (orange, yes; gray, no; white, no data). A cell with an asterisk denotes that more than 1 taxon within the clade was delimited. Vertically oriented labels indicate informal group membership for specimens not assigned to a candidate species."

 

[13] Well, to be completely accurate.  One of the species Mike proposed for synonymy was P. vinyardi, under P. gibba.  That confirms the result Hsiu-Ping Liu and I published in the gray literature back in 2021 [14], finding no evidence of disequilibrium between COI and penial morphology.  So in the single particular case of P. vinyardi, the evidence of synonymy is more than just mtDNA sequence.

 

[14] Liu, H-P, and R. T. Dillon, Jr. (2021) Resolving the species status of Surprise Valley Pyrg (Pyrgulopsis gibba) and Vineyard Pyrg (Pyrgulopsis vinyardi).  Report to Stantec Environmental Consulting. FWGNA Circular 6: 1 – 5. [pdf]  For a review, see:

• Just 125 species of Pyrgulopsis in the American West [7Sept22]

[15] Sneath, P.H.A, and R.R. Sokal (1973) Numerical Taxonomy: The Principles and Practice of Numerical Classification.  W. H. Freeman. 573 pp.