Dr. Rob Dillon, Coordinator

Monday, May 11, 2015

Cornhusker Freshwater Gastropods

Kudos to our good friend Bruce Stephen for his thorough review of the freshwater gastropod fauna of Nebraska, just published in the most recent issue of the American Malacological Bulletin.  A pdf download is available from the link below [1].

The surface waters of Nebraska drain entirely to the east, primarily through the broad, sandy Platte River, as well as through the Niobara and Republican Rivers, all tracing slow, braided paths toward the Missouri.  Glaciers extended over the greener, eastern quarter of the state about 10,000 years ago, although the western half of the state seems to have remained a bit too dry.  Today about 40% of the state is planted in row crops, dependent largely on the miracle of modern irrigation.  The other 60% of Nebraska is sand hills and semi-arid plains, typically given over to ranching. 
I am sure that there are many nice things that could be said about Nebraska and its fine citizenry, but the state does not strike me as especially rich in habitat for freshwater gastropods.  So I was mildly surprised to see that our buddy Bruce’s list extended to N = 31 species, from three primary (and hoary!) sources: Tryon 1866, Aughey 1877, and Walker 1906, a scattering of more recent references, and the collections at the University of Nebraska Sate Museum [2].

Actually, the starting number of species exceeded 80.  The biggest challenges faced by our good buddy were the pruning of over 40 synonyms from the 19th-century taxonomy, and the weeding of around 8 - 10 valid nomina apparently introduced to the fields by error.  The taxonomy of the 31 species that emerged from Bruce’s intensive efforts with hoe and hook was neat, clean, and modern [3].

Loyal followers of this blog may remember my post of 20Apr06, entitled “Surveying the Heartland” [4].  That essay was prompted by our good friend Tim Stewart’s review of the freshwater gastropods of Iowa, very similar in scope and methodology to the present work by Bruce Stephen.  And in my post of 23Jan09, I compared the (46 species) fauna of Iowa to that of Indiana in the east and Missouri in the south, identifying 20 species shared by the three boxy Midwestern states, 15 uniquely shared with the former and 6 uniquely shared with the latter [4].

The FWGNA readership may also remember my post of 26Nov08 reviewing a popular guidebook on the freshwater gastropods of Colorado, based on the (1989) work of Shi-Kuei Wu [4].  So with the publication of the present review of the Nebraska fauna, we have available an unbroken transect, extending 1,000 miles from the banks of the Mississippi River at Davenport, across the Great Plains and over the Rocky Mountains to the Colorado River at Grand Junction.

Should we expect to discover that any of our buddy Bruce’s 31 species are unique to Nebraska?  Or might we find the Nebraska fauna perfectly transitional between those of Iowa and Colorado?  The figure at left is a Venn diagram of boxy western states, composed using the same convention I pioneered in my essay of 23Jan09.  The areas of the states are adjusted relative to their freshwater gastropod faunas – the 44 species documented from Iowa [5] rendering it over twice the size of Colorado (with 20 species, ref. 6), Nebraska in the middle.

And we do indeed see a rather smooth malacological transition (perhaps “attenuation” would be more descriptive) moving west from the relatively rich fauna of Iowa to rather poor Colorado.  Setting aside the 16 cosmopolitan species shared by all three states, Nebraska shares 12 uniquely with Iowa and just one with Colorado (Lymnaea bulimoides).  But again perhaps surprisingly, Nebraska does seem to boast two freshwater gastropod species found in neither Iowa nor Colorado: Physa pomilia and Gyraulus crista.

Our buddy Bruce was a bit dubious about the Physa pomilia records, as am I.  The 15 records from S-K Wu (2004-05) predate our modern understanding of the taxon [7].  But the single G. crista record (from Taylor 1960) appears to be bona fide, this (rather boreal) species being documented from Wyoming to the northwest. 

Science is the construction of testable models about the natural world.  This definition I am in the habit of repeating once a week to my Genetics Lab 305L students, 14 weeks per semester.  Historical reviews such as the work just published by our buddy Bruce Stephens serve the important function of providing models, which we malacologists of the present day really ought to test.  The job most certainly is not over in Nebraska, or in Iowa, or indeed in most of the United States of America, sea to shining sea.  But it is well begun.


[1] Stephen, B. J. (2015)  Species composition of Nebraska’s freshwater gastropod fauna: A review of historical records.  American Malacological Bulletin 33: 61 – 71.  [PDF]

[2] The author’s online queries of the collection databases at the USNM, ANSP, UMMZ, and several museums of more regional character field to yield a single freshwater gastropod record from Nebraska.

[3] Well, there are a couple smudges here and there, but I won’t quibble.

[4] My previous posts relevant to the biogeography of Western and Midwestern states, in order of appearance, have been:
  • Surveying the Heartland [20Apr06]
  • Review: Field Guide to the Freshwater Mollusks of Colorado [26Nov08]
  • The Freshwater Gastropods of Indiana [23Jan09]
[5] The fauna of Iowa has decreased by two species in nine years, due to taxonomic progress.  The lymnaeid nomen emarginata now seems to be a junior synonym of Lcatascopium, and the ancylid nomen parallela a junior synonym of F. rivularis.

[6] Wu’s (1989) monograph actually listed 30 freshwater gastropod species.  I have collapsed 15 of his specific nomina into five names as follows.  Lymnaea humilis = obrussa + parva.  Physa acuta = anatina + cupreonitans + gyrina.  Physa gyrina = elliptica + heterostropha + integra + utahensis.  Helisoma trivolvis = trivolvis + scalare + subcrenatum.  Ferrissia fragilis = fragilis + walkeri.  For more on the physid situation in Colorado, see my essay of [14Oct08].

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

Wednesday, April 15, 2015

The heritability of shell morphology in Physa h^2 = 0.819!

That’s the headline in the most recent edition of PLoS ONE, fresh on the news stands Monday morning.  Read all about it from the link below [1].

To place this remarkable statistic in perspective, animal breeders typically consider heritability in the range of 0.2 – 0.4 to be moderate, and heritabilities above 0.4 to be high.  The heritability of egg production in poultry is approximately h^2 = 0.10, milk yield in cattle about h^2 = 0.35, and weight gain per day in swine h^2 = 0.40 [2].  My colleague Stephen Jacquemin and I reviewed scores of estimates for the heritability of various aspects of gastropod shell morphology (marine, freshwater and terrestrial) in 14 peer-reviewed papers published since 1965, finding but one single value greater than h^2 = 0.819 ever reported [3].   For freshwater gastropods, the highest value reported to date (in a much smaller literature!) is h^2 = 0.30 [4].  How did Stephen and I arrive at our an eye-popping result?

I should imagine that most of my readership will be familiar with the shell morphology of the cosmopolitan invasive Physa acuta, figured at right above.  The shell of Physa carolinae, the recently-described [5] inhabitant of southeastern coastal plains figured at left, is distinctly more slender and fusiform by comparison.  The two species hybridize readily, although the F1 are almost entirely sterile [6].

Stephen and I crossed four pairs of acuta, four pairs of carolinae, and four axc hybrid pairs, rearing all 24 parent animals in standard conditions to age 20 weeks.  We then raised 5 F1 progeny from each of these 12 crosses to age 20 weeks in identical conditions.  And for the entire set of 24 parents plus 60 F1 offspring we took six “classical” linear measurements of the shell and digitized 11 landmark points.

The figure below shows the regression of the simple shell length of the 12 sibships on their mid-parent values, Y = 0.429x + 0.295.  The slope of the regression line estimates the narrow-sense heritability of shell length in Physa as conventionally measured, h^2 = 0.429 (s.e. = 0.139), significant at the (adjusted) 0.008 level.

Stephen and I performed similar calculations for our five other simple linear measurements, the first and second principal components extracted from both the correlation and covariance matrices of these measurements, scores on the first three relative warp axes from a geometric analysis, and centroid size.  The heritability estimates for all 14 of these variables, with their p-values adjusted for multiple comparisons, are shown in Table 2 of our paper downloadable below.  And our headline estimate of h^2 = 0.819 (s.e. = 0.073) is for variance on the first relative warp axis (RWA1). 

Now if overall “shell size” is defined as the summed distance from each of the 11 landmarks to their joint centroid, variance on RWA1 is significantly correlated with shell size at the 0.001 level.  So are almost all of the other 12 variables we measured (see Table 1 of our paper).  This implies that, as strikingly heritable as variance on RWA1 most certainly is, such variance may not be especially useful for inferring evolutionary relationships among natural populations of freshwater gastropods, which are inevitably composed of mixed ages.

Thus the second-most interesting result reported in the paper by myself and my buddy Stephen may not be the heritability of RWA1, but the h^2 = 0.312 (s.e. = 0.123) we estimated for score on RWA2.  This variance is not apparently correlated with overall shell size, and hence might (with some disclaimers) find application to populations of freshwater gastropods sampled from the wild.

And what might our first-most interesting result be?  I think it is the fact that Stephen and I were able to uncover any significant heritability in any aspect of freshwater gastropod shell morphology whatsoever.  The phenomenon of ecophenotypic plasticity is so pervasive in populations of freshwater gastropods as to warrant a separate heading in the blog index at right above, with 13 entries to date.  My stack of peer-reviewed papers documenting plasticity of shell morphology in freshwater snail populations stands 35 deep.  So quoting directly from the concluding paragraph of this our most recent addition to the literature, “Against such a background, the results reported in the present work can be viewed as providing a small measure of balance.”


[1] Dillon, R. T., Jr. & S. J. Jacquemin (2015)  The heritability of shell morphometrics in the freshwater pulmonate gastropod Physa.  PLoS ONE 10(4): e0121962. [html] [pdf]

[2] Falconer, D. S. & T. F. C. Mackey (1996) Introduction to Quantitative Genetics, Fourth Edition.  Essex: Pearson Education Ltd.

[3] Conde-Padin, P. et al (2007)  Genetic variation for shell traits in a direct-developing marine snail involved in a putative sympatric ecological speciation process.  Evolutionary Ecology 21: 635-650.

[4] Chaves-Campos, Coghill, Al-Salamah, DeWitt & Johnson (2012) Field heritabilities and lack of correlation of snail form and anti-predator function estimated using Bayesian and maximum likelihood methods.  Evol. Ecol. Res. 14: 743-755.

[5] TRUE CONFESSIONS: I described a new species. [7Apr10]

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

Monday, March 30, 2015

See You In Milwaukee?

 SFS 2015

The Society for Freshwater Science will be meeting on the sun-kissed shores of America’s Dairyland May 17 -21.  And once again yours truly has volunteered to man the “Gastropoda” booth at the Taxonomy Fair Wednesday afternoon the 20th.  So dig all those vials of juvenile physids out of that box under your sink, toss them loose into your checked luggage, and type MKE into your favorite online travel site today.

The scientific program looks super, as usual.  Our good buddy Sean Sullivan of Rithron Associates has organized a special session on “Invertebrate Systematics and Faunistics” that promises to be a rip-snorter!  There’s still time to register, but you must hurry.  Check out the meeting website (linked from the image above) for all the details.

Tuesday, February 24, 2015

Updated Maps for the FWGNA Project

We are excited to announce that a fresh set of pdf maps detailing the ranges of all the freshwater gastropod species inhabiting Atlantic drainages from Georgia to the New York line are now available for download from the FWGNA site.  This is the first significant update of FWGNA mapping coverage since ever.

As our legions of loyal users will fondly recall, the oldest sections of the FWGNA website featured downloadable pdf dot maps showing the detailed distributions of freshwater gastropods in South Carolina (2005), North Carolina (2005), Georgia (2006) and East Tennessee (2011).  But neither our Virginia site (2011) nor our Mid-Atlantic site (2013) ever featured pdf dot maps.  And our maps of Georgia and Carolina distributions have gone obsolete in the interim.
 Pleurocerid map
So the fresh set of range maps now available for download integrates seamlessly with the version of the FWGNA site we rolled out in October of 2013, based on 11,471 records of 68 freshwater gastropod species and subspecies inhabiting the Atlantic drainages of nine states [1].  These 68 taxa have been divided into 26 sets of two or three related species each (in most cases), and mapped in sets as a tool for the exploration of potentially interesting joint distribution patterns.

As an example, click on the thumbnail above to download a pdf map comparing the distributions of Pleurocera proxima, P. virginica, and P. semicarinata.  You will see very little overlap between these three widespread pleurocerids, proxima ranging throughout small softwater streams of the Blue Ridge and upper Piedmont from Georgia to Virginia, semicarinata inhabiting small hardwater streams in the Great Valley of Virginia, and virginica in the streams and rivers of the lower North Carolina Piedmont, spreading northward.

By way of contrast, click on the thumbnail below left to compare the ranges of the hydrobiids Littoridinops tenuipes, Notogillia sathon, and Spilochlamys turgida.  While populations of Littoridinops demonstrate specialization on a unique (freshwater tidal) habitat up the entire length of the Atlantic Coastal Plain, Notogillia and Spilochamys are positively associated, very strikingly tending to occur together in a narrow patch of central Georgia.
 Hydrobiid map

A complete set of updated maps every bit as interesting as these are available today from the FWGNA site for the entire freshwater gastropod fauna of US Atlantic drainages.  Visit any of the 68 separate species and subspecies covered, scroll down to the “Supplementary Resources” heading, click on the “Atlantic drainages” link, and enjoy!

We are pleased to acknowledge a great debt of gratitude to Mr. Matt Ramsey, an undergraduate archaeology student here at the College of Charleston with a bright future ahead of him.  Great job, Matt!


[1] Freshwater Gastropods of Mid-Atlantic States [30Oct13]

Thursday, January 8, 2015

What I Thought I Knew About Goo

When I posted my first essay on the egg masses of pulmonate gastropods [1] way back in September, I imagined that I was embarking on a very short series, offered as a service to the larger community of generally-trained aquatic biologists and interested amateurs who might be googling about the internet, trying to identify gelatinous blobs.  I had no idea that the series would extend into the New Year, and turn into a parable plumbing the depths of our collective ignorance regarding fundamental aspects of the biology of even the most commonplace bugs and slugs in the most mundane environments.  Or that I would expose my own personal hubris to imagine that I am somehow exempt from the folly.

In the second installment of this series, I presented evidence from Quebec suggesting that the large pulmonate gastropod Lymnaea megasoma might lay string-like gelatinous egg masses of bright green embryos.  But in my third installment, I was forced to conclude that photos depicting string-like gelatinous egg masses of bright green embryos from Maine and Nova Scotia did not illustrate the egg masses of L. megasoma.  I shared my jpeg correspondence with Mr. Tom Pelletier of askanaturalist.com, who sent me the initial photos from Maine and Nova Scotia in June, and then followed up with additional photos showing a cloud of fuzzy specks emerging, decidedly unmolluscan in character.  Mr. Pelletier hypothesized (at the time) that those specks might represent the larvae of a chironomid midge.  One might think that this would conclude the matter.

But just as I was placing a period at the end of my third installment in November, I received yet another email from the extraordinarily conscientious Mr. Pelletier, containing yet another set of jpeg attachments which would call into question even that tiny little bit I thought I knew about goo.

In late November Mr Pelletier introduced me to Mr. Trevor Vannatta, a graduate student working on a parasitological survey at the University of Minnesota in Duluth.  And Mr. Vannatta, by happy fortune, had spent his summer collecting a variety of local lymnaeid snails, including L. megasoma.  And at some point during captivity, possibly as a consequence of shifting into the refrigerator, one of Mr. Vannatta's L. megasoma laid an egg mass in the Petri dish in which it was contained.

It is hard to imagine anything less string-like than the gelatinous mass shown above.  The bona fide L. megasoma egg mass depicted in Mr. Vannatta's jpeg attachments, as forwarded by Mr. Pelletier, is large but otherwise indistinguishable from typical lymnaeid egg masses of the sort we figured back in September.

Is it possible that L. megasoma lays dimorphic egg masses, stringy-green in lakes and flat-typical in Petri dishes?  At 15 cm, the Quebec egg masses we depicted in October do still seem significantly larger than the insect masses we illustrated in November.  In any case, the egg mass morphology of L. megasoma needs confirmation.

And meanwhile, I have found some consolation [2] watching from the CC line as our hero, Tom Pelletier, has continued his mighty struggles to figure out exactly what did lay those gelatinous masses of bright green embryos from Maine and New Brunswick we featured in November.  After exploring the chironomid hypothesis at great length he ultimately turned to a caddisfly hypothesis, specifically large-bodied species of the genus Phryganea or Agrypnia, which lay egg masses in loops, rather than linear strings [3].  Mr. Pelletier posted his essays #2 and #3 on the entomological side of this gooey mystery at askanaturalist.com in mid-December, which make most interesting reading, from the links below [4].

What has stricken me through this entire 5 month and 4 + 3 = 7 essay saga is the insularity of all the research communities involved.  Not only are we freshwater snail people completely ignorant regarding the egg masses of aquatic insects, I don’t think the caddisfly community is especially aware of the chironomid midge community, and vice versa.   And I don’t think that the algal symbiosis community knows anything about any of us.

In November I cited a 1994 paper on the symbiotic association between algae and amphibian egg masses authored by Pinder and Friet.  A couple of excellent works [5] have been published more recently, however, including a very thorough review by Kerney in 2011.  And although the algae/amphibian symbiosis seems to have attracted a great deal of attention over 120 years of study, the (identical? analogous?) symbiotic association between algae and aquatic invertebrate eggs (of all sorts) seems to have remained completely undocumented in the primary literature.

Is the same algal species, generally identified as Oophila ambystomatis in frog and salamander eggs, involved in all these symbioses, invertebrate and vertebrate?  How do the algae become so tightly associated with all these diverse embryos, inside their diversity of gooey matrices?  And is the symbiosis mutualistic in all these cases?  Obligately?  And why do we spend billions of dollars bouncing satellites off comets when such profound mysteries quietly float at the end of the docks in our own backyards?  Mystery on top of wonder, upon wonders.


[1] Our series thus far:
  • The Egg Masses of Freshwater Pulmonate Snails [26Sept14]
  • The Egg Mass of Lymnaea (Bulimnea) megasoma [17Oct14]
  • A Remarkable Convergence of Goo, Or, Perils of a Jpeg Naturalist [11Nov14]
[2] Perhaps this is schadenfreude.  I confess.   

[3] These large, gelatinous egg loops are typically attached to debris and vegetation several feet below the surface of northern lakes.  But wait, don’t adult insects have wings?  Are female caddisflies diving into cold, northern lakes like cormorants?  Wonder on top of wonders.

[4] Tom Pelletier’s series:
  • What is this bright green string of eggs? Part 1 [19Nov14]
  • What is this bright green string of eggs? Part 2 [17Dec14]
  • What is this bright green string of eggs? Part 3 [19Dec14]
[5] Kerney, R. (2011)  Symbioses between salamander embryos and green algae.  Symbiosis 54: 107-117.  Graham, R. R., S. A. Fay, A. Davey and R. W. Sanders (2013)  Intracapsular algae provide fixed carbon to developing embryos of the salamander Ambystoma maculatum.  J. Exp. Biol. 216: 452-459.

Thursday, December 4, 2014

Spur-Of-The-Moment Workshop

In recent years I have occasionally fielded heart-felt requests to organize some sort of workshop on the biology of freshwater gastropods, especially focusing on identification skills.  I was part of an FMCS committee to conduct one such effort in Tuscaloosa in 2004 (to mixed reviews), and I myself led a workshop more narrowly focused on the Pacific Northwest gastropod fauna in Missoula in 2006 [1].  But we've had nothing in recent years.  At least, not around here.

So in the last couple days I've been swapping emails with a small delegation from Clemson University about hosting a freshwater gastropod workshop here in Charleston.  My schedule is flexible between now and Christmas, and so is theirs, and it just seems to have sort-of come together.

So everybody is invited to a spur-of-the-moment workshop at The College of Charleston next Monday morning, December 15, 9-12:00 noonish.   No paperwork, no registration fees.  Just zap me an email if you’d like to participate.

I’ll bring out my personal reference collection, which is really rather complete for The East.  I’ll also go out and fetch us some living critters.  We’ll do a couple dissections.  It’s not rocket science but there are a couple tricks I’ll be happy to show you.

Looking forward to it!


[1] Previous workshops:
  • FMCS Gastropod Workshop [19Dec03]
  • Report from Tuscaloosa [23Mar04]
  • Pacific Northwest Gastropod Workshop [23Mar06]

Tuesday, November 11, 2014

A Remarkable Convergence of Goo, Or, The Perils of a Jpeg Naturalist

Editor’s Note.  This is the third in (what will turn out to be) a series of four essays on the egg masses of freshwater pulmonate snails.  It will only make sense if you read my post of 17Oct14 first, and it would help to at least skim my post of 26Sept14 as well.

In the first episode of our saga, we met Mr. Tom Pelletier, the hardworking proprietor of askanaturalist.com.  It was a jpeg attachment that Mr. Pelletier sent me in the spring of 2014, as well as other correspondence I have enjoyed on the general subject of gelatinous blobs in recent years, that prompted me to post my review of pulmonate egg and egg mass morphology in September [1].  So I was not surprised to receive a second email from Mr. Pelletier this past August, with the subject line, “Another question about snail eggs.”

Mr. Pelletier wrote that he had recently received emails from two different readers bearing very similar attached jpegs depicting what might be snail egg masses, one from Nova Scotia and the second from Maine.  Here is what the Nova Scotia correspondent said:

“We are finding these slimy strings of bright green eggs (?) in the lake. They can be found on the wharf poles but the ones in the picture were on the cord for the underwater thermometer. Any idea what they are from?”

And Mr. Pellatier’s correspondent from Maine wrote as follows:  “I found this jelly blob or loop (below) in the water on the ladder to my boat. I thought it was a round blob but it was more of a loop. These dots were bright green in clear jelly.”

Well, thought I to myself, I can knock this ball out of the park!  These attached jpegs quite clearly depict the egg masses of Lymnaea (Bulimnea) megasoma, to which I devoted my entire essay of 17Oct14 [2].  They demonstrate exactly the same (very distinctive!) morphology, and have been collected from exactly the same habitat type, in exactly the same (chilly) range.  I congratulated myself that I might be the only person in the world who could, with any confidence, identify these peculiar blobs of goo as freshwater gastropod eggs with any authority.

But being the conscientious and thorough worker that he is, Mr. Pelletier had also sent similar inquiries to a herpetologist, an algae expert, and (cleverly) a researcher with expertise in chironomid midges.  And the next day, Mr. Pelletier reported to me that his chironomid guy “seemed pretty sure” that the peculiar blobs of goo in question were the egg masses of his favorite critter, not ours.

A chironomid midge, are you nuts?  I am not an entomologist, but I have waded through enough clouds of chironomids in my day to know that they are tiny little delicate things, maybe 6 – 8 mm in body length.  How could a 6-8 mm fly lay a 6-8 cm egg mass?

Well, in all candor, I had to confess to Mr. Pelletier that I had never actually laid eyes on an egg mass of Lymnaea megasoma either, nor do I have any significant field experience in lakes at any such northern latitudes, and that everything I think I might know about this entire category of question comes from second-hand reports and jpeg attachments.  So in the end, I concurred with the “chironomid guy” (some of whose correspondence Mr. Pelletier had shared) that somebody, somewhere, ought to hatch these things out.

So the results of the experiment came back in September, and my embarrassment was complete:

Although it may be difficult to identify that cloud of blurry specks emerging from the mysterious blob of goo depicted in the jpeg above, I am personally convinced that they are not hatchling Lymnaea megasoma.  The egg mass of a chironomid midge it would seem to be.

In retrospect, questions of scale have continued to dog me in my long running record of folly and failure as a jpeg naturalist.  When I opened Mr. Pelletier’s August email, I had in mind a 15 cm egg mass such as depicted in last month’s essay.  But the “slimy string of bright green eggs” depicted at the top of this essay is probably no more than about 4 cm long, and a much smaller diameter as well.  And since (it seems to me) both last month’s egg masses and this month’s masses seem to contain about the same number of embryos, I think this month’s embryos may be much smaller as well.  Had the two egg masses been sitting in watch glasses on my bench top, I don’t think I would have been confused.

So have two completely independent elements of the freshwater macrobenthic fauna of the higher latitudes of North America, an insect and a gastropod, independently evolved nearly identical egg mass morphology?  And has the same green algae evolved a symbiotic relationship with both?  Could biology be any more fascinating?

Well yes, it could!  In late August our good buddy Tom Pelletier also called my attention to a 1994 paper in the Journal of Experimental Biology on oxygen transport in amphibian egg masses [3].  The amphibian researchers reported that the eggs of both wood frogs and spotted salamanders up in Nova Scotia are “cohabited by Oophila ambystomatis, a green alga found specifically in association with amphibian egg masses.”  They reviewed a large and hoary literature (going back to 1888!) suggesting that such symbiotic algae may benefit from increased ammonia or CO2 concentrations inside the amphibian egg capsules, and confirmed that, under some conditions, O2 produced by the algae seems to be required for the development of the amphibian embryos.

So the same striking egg mass adaptation may have evolved not twice, but three times independently – bug, snail, and amphibian – all three adaptations depending on the same algal symbiosis.

The sentence above looks like a conclusion, but it is not.  There is yet one more episode in this saga, and it does not end neatly.  Rather, episode #4 will make you question some not insubstantial fraction of what you have read in episodes #2 and #3.  Stay tuned!


[1] The Egg Masses of Freshwater Pulmonate Snails [26Sept14]

[2] The Egg Mass of Lymnaea (Bulimnea) megasoma [17Oct14]

[3] Pinder, A. W. & S. C. Friet (1994)  Oxygen transport in egg masses of the amphibians Rana sylvatica and Ambystoma maculatum: Convection, diffusion and oxygen production by algae.  J. Exp. Biol. 197: 17-30. [PDF]