Evolution, development, and random biological ejaculations from a godless liberal
PZ Myers is a biologist and associate professor at the University of Minnesota, Morris.
…and this is a pharyngula stage embryo.
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Could it not be said that it is improbable that we would have a universe in which life arose anywhere? One answer that might be given is that we do not know whether it is improbable or not. Judgments about a priori probabilities in such cases are arbitrary, and we have no evidence in this case of any relevant empirical probabilities.
Michael Martin, Atheism: A Philosophical Justification, (Philadelphia: Temple University Press, 1990), p. 132.
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Category: Organisms
Posted on: July 14, 2007 9:48 AM, by PZ Myers
It's like a flood of papers on that curious cnidarian worm, Buddenbrockia. Now you can also read about its thoroughly bizarre pattern of development — there are unicellular amoeboids, plasmodial masses, and syncytia involved, so be prepared to be titillated.
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Comments
One aspect of an article I had read on Science Daily which I found interesting is that the Buddenbrockia are useful in studying another parasite, Tetracapsula bryosalmonae:
I wrote a little bit about this on Saturday discussing the convergent evolution aspect.
Posted by: Mike Haubrich, FCD | July 14, 2007 1:14 PM
So these life-history characteristics are myxozoan-like, no? Are there sequences for other myxozoans, and if so are they cnidarian too?
Posted by: Sven DiMilo | July 14, 2007 10:39 PM
Yes and yes, as both papers and both blog posts say.
Posted by: David Marjanović | July 15, 2007 1:12 PM
Yes and most likely, I'd be inclined to say. The recent Science paper mentioned both of the major problems with resolving myxozoan phylogeny - (a) because myxozoans are so derived, their branch lengths are spectacularly long, and (b) because of the difficulty of fully isolating myxosporeans in particular from host tissue, DNA contamination is a serious possibility. Cnidarian relationships for Myxozoa would explain the similarity (and probable identity) of cnidarian nematocysts and myxozoan polar capsules. Some phylogenies do resolve Myxozoa on the bilaterian stem [i.e (Cnidaria, (Myxozoa, Bilateria)] which could indicate that nematocysts are ancestral from cnidarians + bilaterians and were lost in the bilaterian ancestor. While the weight of evidence currently lies with the 'Myxozoa as Cnidaria' scenario, the latter scenario is not impossible.
Posted by: Christopher Taylor | July 15, 2007 10:07 PM
Yes, it seems likely that this worm is a Cnidarian. But I would not say this study nails the thing down. I believe more taxon sampling is needed the break down the long branches (how come no other Myxozoan sequences except Buddenbrockia are included in the study? As noted, some Myxozoan sequences reported in genebank are artifacts from the fish hosts.)
Reading "the small print" (supplementary material):
129 protein sequences from 47 animals and 13 outgroups
- Too good to be true? Yes. More than one third of the gene sequences are missing, particularly 56 Buddenbrockia genes (table S3)
Increasing the amount of phylogenetic information by creating chimeric sequences (e.g. human+dog+cow+rat+mouse, table S2)
-Sounds a little bit like cheating to me...
Choosing taxa on the basis of shortest branch lengths
...and this also. What about if these sequences are somehow special?
WAG+Gamma model
- What is the rationale behind choosing the model of the Bayesian analysis? Just some model?
Four other possible phylogenetic positions of Buddenbrockia could not be rejected.
- Which ones? I really cannot understand figure S2. What are those numbers in the tree?
Simple parsimony grouped Buddenbrockia with Nematodes and Platyhelminthes
-I prefer Bayesian inference, but still. CAT-method should account for across-site heterogenities. Perhaps. How does the missing data affect here?
Posted by: Mikko Kolkkala | July 17, 2007 5:09 AM