On September 21 I put up a post about a rare left-handed mutant of the garden snail, Cornu aspersa, named Jeremy.  (That post explains why snails of only identical coiling can mate, due to their hermaphroditism and the position in which they copulate.)  Nearly all garden snails (and 90% of all snail species) have right-handed coiling, but Jeremy, a one-in-a-million variant, is prized by snail collectors; he also could have started a new species of lefties that was reproductively isolated from right-handed snails. (This has in fact happened with other species in nature. It is the only form of single-generation speciation I know, and requires small and largely immobile populations—like snails.)

University of Nottingham inquiries led to the donation of two other lefties: “Lefty” and “Tomeu”. Sadly for Jeremy, they gave him (or rather it, since these snails are hermaphrodites) the cold shoulder, ignored him, and mated with each other.  Well, that’s good for producing a left-handed race, but not good for Jeremy’s libido.

However, all’s well that ends well, and, as NPR reports, Jeremy finally copulated with another lefty. And then he died.

Camila Dominoske, who wrote the piece, has found a sense of humor in this tragedy. Note the puns.

Jeremy, the rare snail with the left-curling shell whose search for a mate kicked off an international quest, has slithered off this mortal coil.

But there’s one last twist to the story. Reader, before he died, Jeremy procreated.

That’s right. The little lefty did it.

. . . Jeremy was found dead on Wednesday. But “the sad news comes with a bittersweet twist,” writes the University of Nottingham.

“Shortly before his death, Jeremy was finally able to produce offspring after mating three times with another ‘lefty’ snail, ensuring that his legacy will live on through continuing genetic studies into his rare mutation.”

(Three times! Nice work, Jeremy.)

Here is Jeremy and several left-handed pals (NPR’s caption): Jeremy is the small guy second from right:

The striking thing about Jeremy’s offspring is that even though he mated with another lefty, their kids are all right handed! But this is understandable given the way snail coiling is inherited. I’ll try to explain it without screwing things up (correct me if I err and you know coiling genetics):

The coiling of a snail’s shell is not determined by its own genetic constitution, but by its mother’s!  While it’s not clear whether the eggs were produced by Jeremy or his left-handed mate, both were lefties. You can be a lefty even though you carry the dominant allele for “right-handed” coiling, so long as your mother was a lefty (l/l) but you inherited a right-handed allele from “dad” or are a mutant (you are L/l). All such offspring of the l/l  X L/l cross will be left-handed because their mother carried the genes for left-handedness, but you yourself could carry (but not express) the genes for right-handedness. I suspect Jeremy (and/or his mate, it’s not clear who produced the eggs) were both L/l snails but didn’t express the “right-handed” L” allele. However, their offspring would: if Jeremy was L/l and acted like the egg-producing “mother” (remember, they’re hermaphrodites), then his own genotype would determine the coiling of his offspring, and all of his own kids would be right-handed, since the product of L (right) is dominant over that of l (left) in the egg cytoplasm.  This is called maternal inheritance: an individual expresses its mother’s genetic constitution rather than its own, though it passes on its own genes to the next generation.

Here’s an analogy: suppose that we look at human eye color and assume that the brown allele (B) is dominant over blue (b), but that eye color is maternally inherited (it’s not; our eye colors reflect our own genetic constitution, not our mother’s; this is a hypothetical). Under maternal inheritance, if your mother was blue-eyed (bb) but mated with a homozygous (BB) brown-eyed male, all the offspring would still be blue-eyed because they’re showing their mother’s genotype, not their own. But every female offspring, being B/b, with brown being dominant, would produce all brown-eyed offspring, regardless of who they mated with.

This is very different from what you’d see if eye color were inherited normally, as it is. In that case the original cross would produce all brown-eyed offspring and the next generation could produce a mixture of brown or blue, depending on whom they mated with.  This form of inheritance, which differs from that seen by Mendel with his peas, was first worked out by a Drosophila geneticist: Alfred Sturtevant, who tested and confirmed his theory in further crosses using a different species of snail.

So what we have here is Jeremy and his mate having mothers homozygous for the left-coiling gene, but themselves carrying dominant right-handed alleles, perhaps because their own mothers had had a rare mating with a righty.

No worries, though, for the left-handed gene is still there in Jeremy’s offspring, even if they show right-handed coiling; further judicious further crosses can and will produce a batch of other lefties. Jeremy’s genetic legacy will live on!

That digression might have confused non-biologists (and I might even have screwed it up a bit), but what’s clear is that we know why two lefties can mate and produce all righties.

If you got through that, here’s a treat from the NPR site: Lydia Hiller’s rendition, in two parts, of “The Tragical Ballad of Jeremy the Left Twisting Snail”. She characterizes Jeremy’s coiling as a “birth defect,” but it’s not: it’s the expression of a rare allele.

RIP Jeremy. We don’t know whether snails get a form of pleasure from copulating, or if it’s just an imperative without a qualia reward, but I hope Jeremy had some fun before he shuffled off this mortal coil.