Monster mouse

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The capybara is the current champion for rodents of unusual size — it weighs about 60kg (about 130 pounds); another large rodent is the pakarana, which weighs about a quarter of that. Either one is far too much rattiness for most people to want hanging around.

Now there’s another king of the rodents: Josephoartigasia monesi, which is estimated to have tipped the scales at about 1000kg, over a ton. Don’t worry about getting bigger rat traps; these beasties have been extinct for perhaps 2 million years. I’ve put a few pictures from the paper describing this new species below the fold.

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Where do the hagfish fit in?

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Hagfish are wonderful, beautiful, interesting animals. They are particularly attractive to evolutionary biologists because they have some very suggestive features that look primitive: they have no jaws, and they have no pectoral girdle or paired pectoral fins. They have very poorly developed eyes, no epiphysis, and only one semicircular canal; lampreys, while also lacking jaws, at least have good eyes and two semicircular canals. How hagfish fit into the evolutionary tree is still an open question, however.

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I want a heart in a jar

A lab at the University of Minnesota has done something cool: they’ve grown a functioning heart from stem cells. The problem with building complex organs in a lab is that their normal construction required an elaborate context in the developing embryo, something that is impossible to replicate, short of just growing the whole embryo. The Doris Taylor lab did something very clever: they took an adult rat or rabbit heart and stripped it of its cells, leaving behind a scaffold of nonliving connective tissue. Then they recellularized it with stem cells, and they differentiated appropriately to make a new, beating heart.

They’ve got a long way to go yet — the resynthesized hearts only beat with 2% of the strength of the normal adult heart — but it’s a good start.

You can watch a video describing the work. Warning: it does show one dead rat and a guy with a knife, and there are pulsing pink blobs of hearts in glass chambers, so it may not be for everyone.

Neurulation in zebrafish

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Neurulation is a series of cell movements and shape changes, inductive interactions, and changes in gene expression that partitions tissues into a discrete neural tube. It is one of those early and significant morphogenetic events that define an important tissue, in this case the nervous system, and it’s also an event that can easily go wrong, producing relatively common birth defects like holoprosencephaly and spina bifida. Neurulation has been a somewhat messy phenomenon for comparative embryology, too, because there are not only subtle differences between different vertebrate lineages in precisely how they segregate the neural tissue, but there are also differences along the rostrocaudal axis of an individual organism. A recent review by Lowery and Sive, though, tidies up the confusion and pulls disparate stories together.

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Evolution of vertebrate eyes

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A while back, I summarized a review of the evolution of eyes across the whole of the metazoa — it doesn’t matter whether we’re looking at flies or jellyfish or salmon or shrimp, when you get right down to the biochemistry and cell biology of photoreception, the common ancestry of the visual system is apparent. Vision evolved in the pre-Cambrian, and we have all inherited the same basic machinery — since then, we’ve mainly been elaborating, refining, and randomly varying the structures that add functionality to the eye.

Now there’s a new and wonderfully comprehensive review of the evolution of eyes in one specific lineage, the vertebrates. The message is that, once again, all the heavy lifting, the evolution of a muscled eyeball with a lens and retinal circuitry, was accomplished early, between 550 and 500 million years ago. Most of what biology has been doing since is tweaking — significant tweaking, I’m sure, but the differences between a lamprey eye and our eyes are in the details, not the overall structure.

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Drugs for brains

Here’s an interesting question: “if you could take a pill which enhanced attention and cognition with few or no side effects, would you?”

Shelley says yes. Janet says no. I say it depends on that qualifier, “few or no side effects” — if that were true, I’d say “Yes! Gimme more!” This is no dilemma at all.

Of course, that’s cheating. There’s no such thing as a drug that has no side effects. The real dilemma would crop up if a cognitive enhancer were available that did have problematic side effects — then my worry would be that pressure to succeed in my classes would be driving students to harm themselves in substantial ways. That happens already. Students take no-doz or skimp on sleep to do well, so there is some unavoidable harm from the stress of learning.

So that’s the information I need before I can make any decision — this is an issue that requires weighing costs and benefits, and telling me there is no cost simplifies it too much. For instance, caffeine has costs, but they’re low enough that my choice is to drink in moderation, but not to give it up altogether.

Load-bearing adaptation of women’s spines

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Blogging on Peer-Reviewed Research

Those of you who have been pregnant, or have been a partner to someone who has been pregnant, are familiar with one among many common consequences: lower back pain. It’s not surprising—pregnant women are carrying this low-slung 7kg (15lb) weight, and the closest we males can come to the experience would be pressing a bowling ball to our bellybutton and hauling it around with us everywhere we go. This is the kind of load that can put someone seriously out of balance, and one way we compensate for a forward-projecting load is to increase the curvature of our spines (especially the lumbar spine, or lower back), and throw our shoulders back to move our center of mass (COM) back.

Here’s the interesting part: women have changed the shape of individual vertebrae to better enable maintenance of this increased curvature, called lordosis, and fossil australopithecines show a similar variation.

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