Malacology morning

My wife thought this story about left-handed snails having a competitive advantage, in that they seem to be better able to escape predation by right-handed crabs, was pretty cool. She also recalled that I’d scribbled up something about snail handedness before, so to jump on the bandwagon, I’ve brought those stories over from the old site.

The handedness of snail shells is a consequence of early spiral cleavages in the blastula. It’s a classic old story in developmental biology—everyone ought to know it!

There was also a story last year about shell chirality in Euhadra. There, it wasn’t a matter of predation, but a potential isolating mechanism, and one where mating compatibility and character displacement could play a role.

Everyone can read up on snails while I’m off at class this morning.

Chirality in Euhadra

i-ccbc028bf567ec6e49f3b515a2c4c149-old_pharyngula.gif

Since Coturnix turned me on to this paper on snail chirality in PLoS (pdf), I had to sit down and learn something new this afternoon.

Chirality is a fascinating aspect of bilaterian morphology. We have characteristic asymmetries—differences between the left and right sides of our bodies—that are prescribed by genetic factors. Snails are particularly interesting examples because snail shells have an obvious handedness, with either a left-(sinistral) or right-handed (dextral) twist, and that handedness derives from the arrangement of cell divisions very early in development.

[Read more…]

Spiral cleavage

i-ccbc028bf567ec6e49f3b515a2c4c149-old_pharyngula.gif

Developmental biologists are acutely interested in asymmetries in development: they are visible cues to some underlying regional differences. For instance, we’d like to know the molecules and interactions involved in taking a seemingly featureless sphere, the egg, and specifying one side to go on to form a head, and the the opposite side to form a tail. We’d like to understand why our back (or dorsal) side looks different from our belly (or ventral) side. One particularly intriguing distinction, though, is the left-right axis. For the most part, left and right are nearly identical, mirror-images of one another, but there are also key asymmetries. Your heart, for instance, is larger on the left side than the right, your liver lies mostly on the right side of your abdomen while the stomach arcs to the left, and these arrangements are essential for normal function. Left-right asymmetries are more subtle than anterior-posterior or dorsal-ventral differences, and that makes them especially fascinating.

[Read more…]

Tiktaalik makes another gap

Paleontologists have uncovered yet another specimen in the lineage leading to modern tetrapods, creating more gaps that will need to be filled. It’s a Sisyphean job, working as an evolutionist.

i-b0b25d35216973e6b76df2f5ed9e177d-tiktaalik.jpg

This creature is called Tiktaalik roseae, and it was discovered in a project that was specifically launched to find a predicted intermediate form between a distinctly fish-like organism, Panderichthys, and the distinctly tetrapod-like organisms, Acanthostega and Ichthyostega. From the review article by Ahlberg and Clack, we get this summary of Tiktaalik‘s importance:

First, it demonstrates the predictive capacity of palaeontology. The Nunavut field project had the express aim of finding an intermediate between Panderichthys and tetrapods, by searching in sediments from the most probable environment (rivers) and time (early Late Devonian). Second, Tiktaalik adds enormously to our understanding of the fish-tetrapod transition because of its position on the tree and the combination of characters it displays.

[Read more…]

Anencephalic on parade

I mentioned that I was getting a curious number of hits for the term “anencephaly” the other day, and was wondering what was prompting it. Readers have been sending me strange and obscure bits of news that might be relevant, such as this account of an unusual birth in Nepal.

The neck-less baby with its head almost totally sunk into the upper part of the body and with extraordinarily large eyeballs literally popping out of the eye-sockets, was born to Nir Bahadur Karki and Suntali Karki at the Gaurishnkar Hospital in Charikot.

The article has pictures (if the description above makes you cringe, don’t look), and also reflects a very different attitude: it looks like people put the dead baby in a tray and had a parade, with crowds of gawkers. They also had a refreshingly pragmatic attitude towards the whole unfortunate event.

Nir Bahadur, the father, says he does not feel any remorse for the newly-born baby’s death. “I am happy that nothing happened to my wife,” he said.

That’s an excellent point of view, I think, much more sensible than that of old Senator Fetus Fondler. Our country could do with a little less embryo worshipping and a little more moving on with the important things in life, too.

And, by the way, I think “Suntali” is a really lovely name.

In which I agree with Tom DeLay

Yes, it’s true: DeLay has said something with which I find myself in accord.

Last Tuesday Mr. DeLay spoke at “The War on Christians” conference during which he agreed with the central theme – that there is, indeed, a “war on Christians” in America today. He went on to say that America treats Christianity like a “second-rate superstition.”

I don’t agree with the first bit, of course: there is no “war on Christians”, although I think maybe there should be a rather more work on putting Christianity in its proper place (in the home and in people’s entirely personal beliefs, and out of government, the workplace, and public education). I am happy to see, though, that someone else has noticed that religious beliefs are just glorified superstitions.

There are important questions remaining. DeLay seems to be aware of a rating scale for superstitions with which I am unfamiliar. What distinguishes a second-rate from a first-rate superstition? Is the scale like the burn scale, where a third-rate superstition would be much, much worse than a first-rate superstition, or is it more embarrassing to believe in a first-rate superstition?

Working out the details of his scoring system for superstitions would be a good project for Mr DeLay in his retirement. I daresay he’d even be able to work on writing it up from a jail cell.