Hemichordate evo-devo

Every biology student gets introduced to the chordates with a list of their distinctive characteristics: they have a notochord, a dorsal hollow nerve cord, gill slits, and a post-anal tail. The embryonic stage in which we express all of these features is called the pharyngula stage—it’s often also the only stage at which we have them. We terrestrial vertebrates seal off those pharyngeal openings as we develop, while sea squirts throw away their brains as an adult.

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The chordate phylum has all four of those traits, but there is another extremely interesting phylum that has some of them, the hemichordates. The hemichordates are marine worms that have gill slits and a stub of a tail. They also have a bundle of nerves in the right place to be a dorsal nerve cord, but the latest analyses suggest that it’s not discrete enough to count—they have more of a diffuse nerve net than an actual central nervous system. They don’t really have a notochord, but they do have a stiff array of cells in their proboscis that vaguely resembles one. They really are “half a chordate” in that they only partially express characters that are defining elements of the chordate body plan. Of course, they also have a unique body plan of their own, and are quite lovely animals in their own right. They are a sister phylum to the chordates, and the similarities and differences between us tell us something about our last common ancestor, the ur-deuterostome.

Analyzing morphology is one approach, but this is the age of molecular biology, so digging deeper and comparing genes gives us a sharper picture of relationships. This is also the early days of evo-devo, and an even more revealing way to examine related phyla is to look at patterns of gene regulation—how those genes are turned on and off in space and time during the development of the organism—and see how those relate. Gerhart, Lowe, and Kirschner have done just that in hemichordates, and have results that strengthen the affinities between chordates and hemichordates. (By the way, Gerhart and Kirschner also have a new book out, The Plausibility of Life (amzn/b&n/abe/pwll), which I’ll review as soon as I get the time to finish it.)

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Savage…tolerance

Just in case anyone is concerned that I’ll soften my hardline rejection of all religion just because I’ve assumed fancy new corporate digs, allow me to quote Dan Savage approvingly.

And finally, to Rob in Albany who felt my aside was proof of my intolerance and hypocrisy: Joking about Christianity isn’t evidence that I’m intolerant—hell, I’m perfectly willing to tolerate Christians. I have never, for instance, attempted to prevent Christians from marrying each other, or tried to stop them from adopting children, or worked to make it illegal for them to hold certain jobs. I don’t threaten to boycott companies that market their products to Christians, and I don’t organize letter-writing campaigns to complain about Christian characters on television.

It would indeed be hypocritical for me to complain about fundamentalist Christians who’ve done all of the above to gay people if I turned around and did the same thing to Christians—but, again, I’ve done no such thing. Intolerant? Hell, I’m a model of tolerance! Oh sure, I joked about the Virgin Birth because I think it’s silly and sexphobic. And I’m free to say as much, however unpleasant it is for some Christians to hear. Fundamentalist Christians, for their part, are free to think homosexuality is sinful and unnatural, and they’re free to say so, however unpleasant it is for me to hear. But fundamentalists aren’t willing to just speak their piece, Rob. Nope, they seek to persecute people for being gay, and that’s where their low opinion of homosexuality—which, again, they have an absolute right to hold—transubstantiates into intolerance.

Excellent. As has always been the case, you can continue to expect me to tolerate Christians…but don’t expect me to ever respect Christianity.

(via Stupid Evil Bastard)

Hit him where it hurts

Pat Robertson’s remarks about Sharon—once again blaming human suffering on divine retribution—have put a crimp in his pocketbook. He’s been leading a consortium to open a Christian theme park in Israel, and finally the Israelis have noticed that Robertson is a tasteless bigot and dishonest con-man. A spokesman for the tourism minister says he’s out now.

Mr Hartuv left the door open to continuing the project but only with evangelists who disown Mr Robertson’s statements.

“The contract is still open – just not with Mr Robertson. If there are other Christian leaders, they are most welcome to sign a contract to bring Christian tourists to the State of Israel.

“We want to see who in the group supports his (Robertson’s) statements. Those who support the statements cannot do business with us. Those that publicly support Ariel Sharon’s recovery are welcome to do business with us. We have to check this very, very carefully.”

That’s a mistake. These people are professional hucksters—they shouldn’t trust any of them. And seriously—putting up a food court at the site of the purported miracle of the loaves and fishes? Isn’t that just a little bit tacky?

(via Julia)

Firefly squid

This is a beautiful little animal with a brief and brilliant life.

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Watasenia scintillans is a small (mantle length,~6 cm; wet weight,~9 g), luminescent deep-sea squid, indigenous to northern Japan. Females carrying fertilized eggs come inshore each spring by the hundreds of millions, even a billion, to lay eggs in Toyama Bay (max. depth, 1200 m) and die, thereupon completing a 1-year life cycle.

Watasenia possesses numerous (~800), minute dermal light organs (photophores) on its ventral side. Other organs are scattered over the head, funnel, mantle, and arms, but none is found on its dorsal side. There are five prominent organs beneath the lower margin of each eye. They all emit a bluish light. A cluster of three tiny black-colored organs (<l mm diam) is located at the tip of each of the fourth pair of arms. They emit brilliant flashes of light which are clearly visible to the unaided eye even in a lighted room. Some of the flashes have a cadence resembling that of a terrestrial firefly flashing at night, and thus the squid is known in Japan as the “firefly squid” or “hotaru-ika.”

A billion die every year as a natural part of their lifecycle; all those glittering little creatures dying profligately—Nature is both exuberant and pitiless, it seems.

Tsuji FI (2005) Role of molecular oxygen in the bioluminescence of the firefly squid, Watasenia scintillans. Biochem Biophys Res Commun. 338(1):250-253.

Welcome to the new place!

As you’ve figured out now, I’ve joined the ranks of the many science bloggers at scienceblogs.com. The plaster’s still wet on the walls and there are a few things I still would like to see fixed up here in the new place (my rotating logos will be implemented some time—Carl Buell‘s Brontops will change now and then, pretty as it is; someday I’ll have to see what I can do to get Pirate Mode functioning here, too), but for now it’s a good clean layout and plenty of buckets to pour text into, and that’s all that really matters. Most importantly, with a team of pros managing the behind-the-scenes work and some really powerful servers to handle the pages, I’m hoping the frequent slow-downs and flailing databases of the past are now behind me. Let’s try to kick the tires and have a few hundred-thousand-visitor days to see how well it can all cope, OK?

Let me also reassure (or worry) you with one important thing: I think Seed gets it. When we were negotiating this move, one specific request was that I could be as free here to say what I want as I was on my own server, and I’m confident that that will be the case—so expect me to be as obnoxious as ever, sprinkling little bits of information on my usual abrasiveness to make it all go down smoothly. So, no changes except for the new URL, better performance, and a few quirky features that are gone but may slowly be restored…content will be the same, and there are promises of better things to come. We all win!

Of course, if there are things you really miss, or if you encounter new problems, please do let me know about them, and I’ll pass them onto the good guys who do the real work around here. I’m planning to just put my feet up and babble.