I just put of copy of “Embrace your inner fish” outside my office door. I want it on a T-shirt now.
(via The Austringer)
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
I just put of copy of “Embrace your inner fish” outside my office door. I want it on a T-shirt now.
(via The Austringer)
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.
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.
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.
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.
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.
Pianka speaks out. Nick Matzke has a good post on Pianka at the Thumb, addressing the smear campaign against him*. He links to an interview with the good Dr—what he’s saying is simple sense, common in the biological community, and he’s not endorsing mass murder…he’s talking about conservation and planning ahead. Mims is a “crazy kook” who distorted the story and turned it into screaming match.
Get used to it. This is part of the right-wing strategy to attack the academy: when scientists honestly state bad news (and there is much bad news, and it’s growing), they are going to be rabidly accused of all kinds of outrageous crimes. It’s the new McCarthyism. The majority of us do not support short-sighted policy, we don’t endorse jingoism, we are going to urge people to think before acting, we are going to predict the consequences of bad policy, and we are generally going to be critical of demagogues and fools…and that is being treated as a crime.
*Quite unlike the situation with Paul Mirecki; I can’t help but interpret this to mean you’re going to be left twisting in the wind if the right-wing mobs try to lynch you, and you admit you’re godless.
There are these fossilized embryos from the Ediacaran, approximately 570 million years ago, that have been uncovered in the Doushantuo formation in China. I’ve mentioned them before, and as you can see below, they are genuinely spectacular.
But, you know, I work with comparable fresh embryos all the time, and I can tell you that they are incredibly fragile—it’s easy to damage them and watch them pop (that’s a 2.3MB Quicktime movie), and dead embryos die and decay with amazing speed, minutes to hours. Dead cells release enzymes that trigger a process called autolysis that digests the embryo from within, and any bacteria in the neighborhood—and there are always bacteria around—descend on the tasty corpse and can turn it into a puddle of goo in almost no time at all. It makes a fellow wonder how these fossils could have formed, and what kind of conditions protect the cells from complete destruction before they were mineralized. Another concern is what kinds of embryos are favored by whatever the process is—is there a bias in the preservation?
Now Raff et al. have done a study in experimental taphonomy, the study of the conditions and processes by which organisms are fossilized, and have come up with a couple of answers for me. Short version: the conditions for rapid preservation are fairly easy to generate, but there is a bias in which stages can be reliably preserved.
The Pianka situation is getting very, very ugly. I’ve been chatting with a member of the Texas Academy of Science, and people there are getting death threats over it. Here’s one example of the kind of email they’re getting:
Some fields of science are so wide open, such virgin swamps of unexplored territory, that it takes some radically divergent approaches to make any headway. There will always be opinionated, strong-minded investigators who charge in deeply and narrowly, committed to their pet theories, and there will also be others who consolidate information and try to synthesize the variety of approaches taken. There are dead ends and areas of solid progress, and there is much flailing about until the promising leads are discovered.
Origins of life research is such an unsettled frontier. I wouldn’t want to work there, but the uncertainty and the confusion and the various small victories and the romance of the work do make for a very good story. And now you can read that story in Robert Hazen’s Gen•e•sis: The Scientific Quest for Life’s Origins (amzn/b&n/abe/pwll).
Our speaker at Tuesday’s Café Scientifique, Nic McPhee, has a blog, and gives the speaker’s side of the event. He’s exactly right that our big problem out here is improving community involvement, and getting some interaction with the townie side is going to be one of my goals in setting up next year’s series.
