BATS!!

This is the second essay test that I have written for P.Z.'s developmental class. The style is supposed to be similar to what you would see in Scientific American or The New York Times science section. I hope you guys enjoy it:

Lab rats with wings: The development, genetics and evolution of bat wings

"There were giants in the earth in those days"

There is an article from Wired that highlights some research that is (sorta) about insect development. From the article:

To explore the effects of ancient oxygen levels, VandenBrooks’ team raised dragonflies and 11 other “living fossils,” including beetles and cockroaches, in three habitats with different oxygen concentrations — one at the late Paleozoic’s 31 percent oxygen level, another at today’s 21 percent level and the third at 12 percent from 240 million years ago (Earth’s lowest oxygen level since complex life exploded onto the scene half a billion years ago).
They found that dragonflies and beetles grew faster, as well as bigger, in a high-oxygen environment, while cockroaches grew slower and remained the same size. All but two bug species grew smaller than normal at low concentrations of oxygen.

 *Italics added*
This is super neat! A single environmental factor seems to be having substantial effects on the development of these insects.  Oxygen levels seem to be having most of their effect on the tracheal system of these insects, which is what you would expect, since the trachea are the organs that bring oxygen to insect tissues. They also seem to think that they could use tracheal  measurements from insects trapped in amber to determine ancient oxygen levels.
It would be interesting to see if there are developmental reasons why cockroaches don't respond as quickly to increased oxygen. Could the dragonflies' aquatic larvae impact the process? Or might there be genetic factors that create other growth constraints in cockroaches? Would there be similar effects on arthropods that do not have trachea, but have book lungs? It's neat stuff, but the research was presented at a geological meeting, so the developmental questions were not the ones that were most addressed. Also, they said things like this:

dragonflies and other insect groups do develop and evolve larger body sizes in hyperoxia...

They evolve larger body sizes!? Were the changes in body size heritable?  Has the author never heard of Lamarck? This seems wrong, but I don't know any of the details of the research, so frankly I can't make any better of a judgment than that. I hope to see an article about this at some point, because I really want to know more.

The quote in the title is from Genesis 6:4.

Test 1 (bicoid)

This is the text of the first test that I wrote for P.Z.'s class. The test is supposed to be free-standing essay written for a popular audience, so it seemed perfect for the blog. It's long, but the topic is pretty cool, so you should read it. The title is Bicoid: Evolution of novelties.

"Since I cannot prove a lover, To entertain these fair well-spoken days, — I am determined to prove a villain"

One of the first things that we have learned in our developmental biology class is that development is hierarchical. Which is to say that a cell that becomes a liver cell will not change back to anything else. Moreover, the cells that derive from that cell will also be liver cells, and they too cannot reverse their fate. This is a story about hierarchical determination in a quite extreme form.

Copidosoma floridanum is one of the strangest animals around. It is a parasitoid wasp, animals that are normally compared to the Hollywood monster “Alien”, but frankly, this is far stranger. The adult is free living, and flies around laying eggs in moth caterpillars. One of those eggs will then divide rapidly inside the moth, forming not one but many, many larvae. Most of those larvae will begin the mundane parasitoid task of devouring the moth from the inside out while it is still alive. But some larvae will develop early and gain bodies developed for swimming and fighting. These larvae move through their host’s body, seeking out and killing any other parasitoids that they find. They ensure the survival of their sisters by wiping out everyone else. This “soldier caste” of larvae will never make it out of the moth; they die before adulthood, sacrificing themselves for the benefit of their clone siblings (fig. 1).

Fig 1: These pictures show the two types of larvae. Soldier caste on the left, reproductive caste on the right. From Donnell et al. 2004.

This is a long set-up to a bad pun

As our developmental biology class ramps up after P.Z.’s unfortunate illness, we have begun to read and discuss Sean Carroll’s book Endless Forms Most Beautiful. At the end of the fourth chapter of that book, Carroll writes:

“Francois Jacob has pointed out that all of our explanatory systems, whether mythic, magic, or scientific, share a common principle. They all seek, in the words of physicist Jean Perrin, ‘to explain the complicated visible by some simple invisible.’”

I think that Jacob, a member of the “Indiana Jones society of scientists who fight Nazis”, is likely correct that scientific and religious systems of knowledge attempt to fulfill a similar role. The difference between the two is that science has to provide evidence for the “simple invisible” that it postulates. To do this we must find a way to illuminate the hidden mechanisms that drive our natural world. The experiments that manage to most clearly show these mechanisms are the ones that become famous. The elegance with which finch beaks or a double slit experiment can reveal natural truths is what makes them so compelling.
Carroll recognizes the importance of making invisible mechanisms apparent, and compares it to our ability to visualize gene expression using florescent antibodies or other molecular mechanisms. However I think Carroll sells himself short. Even before there were the means to make pretty pictures of embryos with glowing stripes, we could still visualize the effects of “master genes” such as the hox genes. We did this by making monsters. Although it may be less elegant than the newer molecular tools, one can gain insights into the process of development by fucking up embryos and examining the horribly deformed monsters that result. The second chapter of Carroll’s book is thick with examples of scientists who created monsters to learn about development. Although the experiments may seem slightly macabre, the discoveries that result are often really neat. One of my favorite examples that we’ve discussed thus far is the discovery of the zone of polarizing activity.
While an embryo is developing, how does each cell know where it is in the body? How do pinky cells know to make pinkies, and thumb cells know to make thumbs? Saunders and Gasseling (1968) discovered one clue to this puzzle by creating mutant chicken arms. Birds have lost the digits that would correspond to our thumb and pinky, leaving them with three digits on their limbs. But when these researchers took early embryos (before they developed anything beyond stumpy limb buds) and moved bits of the developing limb around they created some interesting mutants. When they removed the back of a limb bud from one developing chicken and attached it to the front of the limb bud in another, the resulting wing had two hands. The small number of transplanted cells were able to direct the formation of an entirely new hand (see figure).

This finding showed that a small number of cells could inform the surrounding cells about their relative positions. In essence, saying, “I’m making a ring finger, if you are close to me, build a middle finger and if you are far away make a pointer finger” (remember that birds have only three digits per wing). Saunders and Gasseling called the area of cells that organized the rest of the limb the “zone of polarizing activity” or ZPA. The ZPA provides information about its position by expressing the sonic hedgehog gene. This creates a protein that diffuses out to the surrounding cells. If there is a lot of the protein around, a cell knows that it’s close to the ZPA and that it should make the back of a wing. If the protein is scarce, a cell is far from the ZPA and should build the front of a wing. The ability of a small number of cells to organize the development of larger structures through the expression of genes is important throughout development.

After Saunders discovered the ZPA, he left the scientific world and started a restaurant franchise. The tagline was: “Colonel Saunders, the chicken wing that twice as good as the competition!”

Fertilization

Because this is a blog about development, perhaps the first post should be called fertilization.

My name is Logan Luce; I am a senior biology major at the University of Minnesota Morris. I am taking a developmental biology course from P.Z. Myers, a man who moonlights as a horrible amalgamation of scientist and atheist, blogger and firebrand. P.Z. has decided to have all of his developmental students start blogs, presumably for the purpose of mocking the diminutive number of hits that we can eke out of the internets. He has hinted that the final exam will be crashing a poll.


A bit about me and the name of this blog: I am primarily interested in ecology and evolutionary biology, and am fascinated by insects and dinosaurs. If you assume that my interests are the same a prototypical 8 year old boy, you would be close to the mark. A naiad is the larval stage of an insect in the orders Odonata, Ephemeroptera or Plecoptera. These insects exhibit incomplete metamorphosis, so the larvae appear similar to the adult except for the lack of fully developed wings or genetalia. Unlike the larvae of other some related insects (such as grasshoppers) naiads do not live in the same environment as the adults that they later become. A naiad may begin as a badass killing machine that hunts in the bottom of a lake, but it will become a badass killing machine that hunts in the sky. Development from a naiad involves moving from freshwater into the air, losing gills and gaining wings, while still maintaining a similar sort of form. As an undergrad that hopes to become a grad student doing cool research on neat bugs someday, I commiserate with the naiad. I don’t want to change too much, but I’m looking foreword to moving to a new environment and the possibility of gaining wings...
and 360 degree vision...
and the ability to hunt and kill on the fly.

(That's what grad school is like, right?)