Thursday, October 20, 2005

Is this sad?

` I was reading this today...

` Independent specialization of arthropod body segments has led to more than a century of debate on the homology of morphologically diverse segments1, 2, each defined by a lateral appendage and a ganglion of the central nervous system.
` The plesiomorphic composition of the arthropod head remains enigmatic because variation in segments and corresponding appendages is extreme. Within extant arthropod classes (Chelicerata, Myriapoda, Crustacea and Hexapoda—including the insects), correspondences between the appendage-bearing second (deutocerebral) and third (tritocerebral) cephalic neuromeres have been recently resolved on the basis of immunohistochemistry1 and Hox gene expression patterns3, 4. However, no appendage targets the first ganglion, the protocerebrum, and the corresponding segmental identity of this anterior region remains unclear5.
` Reconstructions of stem-group arthropods indicate that the anteriormost region originally might have borne an ocular apparatus and a frontal appendage innervated by the protocerebrum6. However, no study of the central nervous system in extant arthropods has been able to corroborate this idea directly, although recent analyses of cephalic gene expression patterns in insects suggest a segmental status for the protocerebral region7, 8, 9, 10.

` Here we investigate the developmental neuroanatomy of a putative basal arthropod11, the pycnogonid sea spider, with immunohistochemical techniques. We show that the first pair of appendages, the chelifores, are innervated at an anterior position on the protocerebrum. This is the first true appendage shown to be innervated by the protocerebrum, and thus pycnogonid chelifores are not positionally homologous to appendages of extant arthropods but might, in fact, be homologous to the 'great appendages' of certain Cambrian stem-group arthropods.

` And I realized something: "I am seriously out of touch with my inner biologist!"
` Sadly, I can only understood 3/4 of what that means! Am I doomed to continue forgetting what I've learned over the years?

` What is to become of me!??!

` This post brought to you by a severe bout of sarcasm. Laugh monkeys, laugh!


Galtron said...

Exweeze me? Monkey? I am a hummingbird, thank you!

Aaron said...

It was so hard to read that piece and it didn't seem to say much. How do they measure nevrous system activity in insects anyway?

S E E Quine said...

` Aw, well, it's just a summary. They're basically talking about how part of the modern arthropod brain doesn't seem to correspond to a bodily segment... except for in sea spiders, which have fairly primitive features.
` According to the study, the sea spider has appendages which at least seem to correspond to arthropods that lived millions of years ago, rather than anything found in other modern arthropods.
` A 'living fossil' body part, if you will.

` Here, they measured the arthropods by looking at chemical and immune reactions in the tissue under a microscope in order to determine what's hooked up to what.
` However, I'm not very sure how they do that, what they use, or what's involved in it.

Galtron said...

I thought it was describing the [insert surname of some blood-related slimeballs] family.