Dr. Rob Dillon, Coordinator

Wednesday, October 3, 2018

To Identify a Physa, 1989

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  To Identify a Physa, 1989.  Pp 163 – 168 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays FWGNA Project, Charleston, SC.

Faithful readers of this blog may remember a series of essays I posted in the spring of 2014, occasioned by the death of Dr. George A. Te [1].  In those essays I chronicled the development of our understanding of the systematics of the North American Physidae through the years 1971, 1975, and 1978.  Beyond that date, however, I let the subject drop.

Let’s pick that story up again, shall we?  What will follow, over the next few months, will be an awkwardly-personal series of essays in which I share trivial tidbits, poorly-recalled anecdotes, and quasi-factual reminiscences about the progress that my colleagues and I have been able to make toward a fuller understanding of the evolutionary biology of the Physidae over the last 30 years.
Mate choice experiments
And colleague number one, from the humble beginnings of this research effort to the present day, has been my good friend, Dr. Amy R. Wethington.

Amy arrived at The College of Charleston in the fall of 1988, initially as a graduate student in our marine biology program.  But she realized, rather quickly, that her undergraduate training in biochemistry from Clemson had not prepared her for graduate studies in Biology.  So by the spring of 1989, she was an undergraduate biology major at The College, working with me on the genetics of the commercially-important hard clam, Mercenaria.  And one afternoon our conversation somehow turned to the subject of freshwater gastropods [2].

A couple years previously another graduate student and I had discovered a population of the tropical planorbid, Biomphalaria, in an ornamental pond at Charles Towne Landing State Park, right around the corner from my home in the West Ashley suburbs [3].  So, I suggested to Amy that we might undertake a study of sperm storage in Biomphalaria.  Essentially, our idea was to collect a batch of adult snails, isolate them in one-quart Ball jars, collect their eggs serially, hatch and rear their F1 babies, and use polymorphisms at allozyme-encoding loci to determine at what point isolated Biomphalaria depleted their reserves of allosperm (i.e., a partner’s sperm) and switched over to autosperm (i.e., began to self-fertilize).  We even hoped to be able to see multiple insemination and sperm competition, if we could find a couple of good genetic markers.

So on May 16, 1989 Amy and I did indeed drive over the Ashley River bridge to Charles Towne Landing, collect a big batch of adult Biomphalaria, and isolate 30 of them in Ball jars, according to plan.  They laid some egg masses, in a desultory sort of way.  But our allozyme gels revealed disappointingly low levels of genetic variation.  The Charles Towne Landing Biomphalaria population did not seem to demonstrate any high-frequency polymorphisms we could count on.

But thanks be to Providence, we had also collected a big batch of Physa that afternoon at the “CTL pond,” perhaps more out of idle curiosity than anything else.  We referred to them as “Physa heterostropha pomilia (Conrad),” which is what George Te would have called them, had he still been active in the discipline at the time, approximately [4].  Physa (or Physella) heterostropha pomilia was the commonplace identification given to all physids everywhere in the American South in 1989.

And not only were our “Physa heterostropha pomilia” auspiciously polymorphic, they began to reproduce like crazy, most of them laying large, healthy egg masses their first 24 hours in culture.  So, we advanced the parent snails to second jars, and pretty much all of them laid second egg masses during their second days.  And third egg masses during their third days.  And very soon, we were out of jars.

Amy Wethington and charges, May 1989
Well, the jars were a bad idea.  They were too big and too expensive.  And they each had an inch of aquarium gravel in the bottom, which was an even worse idea.  So right around this time I had a conversation (or email exchange?) with our good friend Dr. Margaret (“Peg”) Mulvey.  Peg was working at the Savannah River Ecology Lab at the time, and she had a great deal of experience culturing the medically-important planorbids.  And she suggested 10 oz plastic drinking cups, with disposable Petri-dish lids.

I have read, in much weightier and more learned reviews, that scientific advance is dependent upon the advance of technology.  I have always visualized Mars Rovers and super-conducting super-colliders.  In studies of the evolutionary biology of the Physidae, however, the key technological innovation turned out to be a 10 oz plastic drinking cup.

The photo above is one of my favorite images I have ever snapped.  It shows Amy in the College of Charleston genetics lab in May of 1989, holding a glass jar of Physa, or maybe Biomphalaria, no way of knowing at this point.  Our experiment on sperm storage is just beginning on the bench top in front of her.  At this early date, you can see just a couple of plastic cups scattered around the tabletop.  That’s our scheme to identify multiple insemination and sperm competition written on the blackboard behind her.

Amy and I ultimately carried our sperm storage experiment for 60 days, conducted our allozyme analysis, and were treated to less-than-spectacular results.  Our paper was rejected by two journals, and even initially (Oh, the slings and arrows!) by our third choice, the American Malacological Bulletin.  But Bob Prezant ultimately relented, agreeing to publish the very first Wethington & Dillon collaboration as a “Research Note” in Volume 9 of 1991 [5].

By that date, however, the research program that Amy and I had begun in 1989 had exploded, ultimately to yield 23 peer-reviewed papers [6], a six-figure NSF grant and Amy’s PhD.  And a great deal of (quite gratifying) follow-up research by a variety of colleagues worldwide, still very much ongoing.

And as our Physa research program exploded, so too did our Physa cultures themselves.  The photo below was snapped just a few weeks after the photo above.  A scattering of ball jars remain in evidence, which were the initial containers for the parent snails, now holding their first sibships of offspring.  And hundreds of plastic cups for subsequent sibships.

Amy and charges, July 1989
That’s actually the College of Charleston’s Genetics 311L teaching laboratory now covered in 10 oz cups.  Or, as the chairman of my department often and vocally stipulated, “instructional space, not research space [7].”  Moreover, almost every square inch of bench top in the student research lab down the hall was covered with Physa cultures by the summer of 1989, eliciting pointed half-jokes from my departmental colleagues to the effect that the projects of their own students were being crowded out by gastropods.

In 1908, an obscure physiologist at Columbia University named Thomas Hunt Morgan had exactly the same problem with fruit flies.  He was also using unwieldy glass culture vessels – half pint milk bottles of smushed banana – and he had a small team of dedicated undergraduates helping him as well, bailing against the dipteran tide.  And what Morgan and his students began to notice, as the weeks rolled by, and thousands of fruit flies passed under their scopes, was variation.  Some flies had different eye colors, some had different wing types, and onward so forth.

How analogous might our experience become with the Physa cultures that covered the College of Charleston Genetics Laboratory in the summer of 1989?  Stay tuned.


[1] Physa systematics in the era of George Te:
  • To Identify a Physa, 1971 [8Apr14]
  • To Identify a Physa, 1975 [6May14]
  • To Identify a Physa, 1978 [12June14]
[2] I'm shocked! Shocked to find that freshwater gastropods are being discussed in this establishment!

[3] Dillon, R.T. and A.V.C. Dutra-Clark (1992) Biomphalaria in South Carolina. Malacological Review 25: 129-130.  [PDF]

[4] As may be recalled from my essay of 12June14 (above), George Te raised the Baker subgenus “Physella” to the full genus level and placed 38 species under it, including heterostropha.  Even back in 1989, I thought that was a bad idea.

[5] Wethington, A.R. and R.T. Dillon (1991) Sperm storage and evidence for multiple insemination in a natural population of the freshwater snail, Physa. American Malacological Bulletin 9: 99-102. [PDF]

[6] This figure is the sum of seven Physa papers by Wethington & Dillon (sometimes with other coauthors), eight by Dillon & Wethington (sometimes with other coauthors), four by Dillon without Wethington, and four by Wethington without Dillon, as of 2018.

[7] When I interviewed at The College of Charleston in the winter of 1982, I was shown Science Center Room 200, the instructional lab where I would be expected to teach Genetics Lab 310L.  The chairman made it clear that a research program was also expected and offered me $5k to start it up.  But in those days, I don’t think there was any “dedicated research space” anywhere at CofC.

That situation was to evolve radically over the next 30 years, to the point that dedicated research space and big-dollar start-up packages were assumed to be essential to attract qualified faculty.  But I never had any.

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