Sunday, November 7, 2010

"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.


  1. Hi Logan, nice blog!

    I don't see why you mention Lamarck. It seems to me that in a hyperoxic environment, heritable mutations leading to larger body size would be able to provide a selective advantage, whereas in a modern standard atmosphere, such mutations would be selected against because they would lead to the organism being too large to breathe efficiently. The change in environment is just providing a backdrop against which heritable changes leading to large size can be enabled and large arthropods can flourish. Nothing to do with inheriting acquired traits.

    Of course, there would still be a limit for terrestrial arthropod size, based on their need to shed their exoskeletons, thus leaving the body unsupported.

  2. Dave,
    It might be the fact that I can only see the abstract, but they don't demonstrate any evolution, only an acquired trait. They could certainly argue that increased oxygen *might* facilitate evolution of larger body sizes would be quite reasonable, but that's not what they say. They say: "insect groups do... evolve larger body sizes" That is not something you can say if you have only observed phenotypic plasticity

  3. Heya Logan! I knew it was you. Didn't know you were one of PZ's students though: LEGENDARY!

    Drop me a line sometime or check out the blog I (occasionally) co-author:

    Hope to see you this winter. I'll buy you a drink.

  4. It could just be a sloppy use of the word "evolve". Higher oxygen levels might encourage selection in favor of genes for large body size, but as you say, this particular experiment doesn't demonstrate that.

    Isn't it possible, though, that an increase in size could be passed on from one generation to the next even without genetic changes? An exceptionally large female mammal might be expected to have larger-than-average babies just because of having a larger body size, even if her size were the result of good nutrition rather than genes.

  5. Infidel:
    I suspect that you are right, and they used "evolve" in slightly too strong of a context. They're only geologists, so I suppose it's forgivable.

    As for the inheritance of non-genetic traits, large mother = large babies will likely be true, but it seems unlikely that that would lead to any long term changes in a population. Epigenetics seem to point to a different way in which non-genetic changes could be heritable, but I don't really know anything about that. Perhaps you should ask ERV.

  6. Carter:
    Hey! I've been thinking about you guys a lot. I think my geology teacher is frustrated with the fact that I stop taking notes and start daydreaming whenever she mentions eskers.

    I will gladly accept your drink this winter. Although if you try to play a "friend card" I might puke.