The next edition of the Tangled Bank will be held at Grey Thumb.blog on Wednesday, 18 Jan 2006. Send in those links to wonderful science writing to tangledbank@greythumb.org,
host@tangledbank, or
me by Tuesday evening.
BioCurious has a nifty methods article on Labeling λ DNA—if you’ve ever wanted to know how to tag a strand of DNA with a bead so you can tow it around with your optical tweezers, here’s the theory (and they’ve got optical tweezers? I am so jealous.)
A reader sent in this little question:
Possible answers:
OK, that settles it. I’m in the wrong research field.
They found breasts moved in a 3D figure of eight and that uncontrolled movement strained fragile tissues and ligaments.
The study suggested as a woman runs a mile, her breasts bounced 135 meters.
The report found each breast moved independently of the body by an average of 9cm for every step taken on the treadmill.
With the average breast weighing between 200 and 300 grams, this movement puts great stress on the breast’s fragile support structure—the outer skin and connective tissues known as Cooper’s ligaments.
I suspect the analysis was…mesmerizing.
The wording was a little unfortunate—I pictured the subject dribbling a pair like basketballs as she runs.
(via Matt Dowling)
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.
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.)
This is a beautiful little animal with a brief and brilliant life.
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.
