Editor's Note. This is the final essay in my four-part series on the egg masses of pulmonate snails. But this was not to be the end of research interest in enigmatic, string-like gelatinous masses of bright green embryos. Mr Trevor Vanatta, whom you will meet in paragraph #4 below, continued to work on the question through the field season of 2015, and by September had obtained some rather definitive results. See Tom Pelletier's blog of 19Dec14 for the (absolutely!) last word.
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.
Notes
[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.