Discovery wants to "demote" fungi.

Here’s an interesting story from the Discovery Channel.

Plants and animals: long lost relatives?

“Yes,” I know you’re thinking, “next question?”.

But wait, the story takes a different approach.

Plants and animals may occupy distinct branches on the tree of life, but they could be more alike than we think.

In fact, green plants and animals enjoy a relatively close evolutionary relationship that has been obscured by a narrow focus on DNA sequences to find relatedness, says biologist John Stiller of East Carolina University.

Plants, fungi and animals are all in a group called the eukaryotes — distinguished by their advanced cellular machinery. But some eukaryotes, most notably the fungi, have long been considered more closely related to animals than plants are.

Stiller’s theory suggests organisms such as fungi should be given a demotion — placed further from animals on the tree — while green plants should get a leg up.

Say again???

Another attribute shared by plants and animals, according to Stiller, is the way the genetic material RNA operates in both groups. In both plants and animals, RNA acts as an intermediary between DNA and the protein it codes for. The enzymes that put RNA to work in a cell are similar in plants and animals, but not present in fungi or other organisms, he said.

It is, of course, utterly inconceivable that the common ancestor to all three groups had this trait which was then lost in fungi. Because fungi are, of course, not a derived group that has been evolving for exactly the same amount of time as plants and animals by definition. Oh no.

Maybe the paper makes a good argument. Maybe plants and animals are sister taxa to the exclusion of fungi. But one thing’s for sure — no one’s getting “demoted” one way or another because this idea of rank was should have been abandoned 150 years ago.

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Update:

See Sex, Genes & Evolution for more insights on the actual hypothesis, which should not be judged on the basis of how it was reported in the press.



8 comments to Discovery wants to "demote" fungi.

  • RPM

    It takes chutzpa to determine evolutionary relationships using a single character.

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  • Shalini

    Maybe the paper makes a good argument.

    Apparently not.

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  • Ian

    Actually the paper doesn’t look too bad (taking a quick look at it, as a non-systematist).

    Stiller’s main point seems to be that, despite the fact that the Viridiplantae (land plants + green algae) usually shows up as a sister group of the Red Algae, and animals, fungi and their respective protist relatives usually for another clade, that there’s evidence that the Viridiplantae are actually closest to the animals. His reasonings is based on:

    (a)while there are putative synapomorphies that unite animals and fungi, there are others that unite animals and plants

    (b)that there are highly conserved proteins/pathways that are shared by plants and animals but not fungi

    (c)the shared sequences that unite Viridiplantae with Rhodophyta may actually have been acquired from their plasmid symbionts (originally cyanobacteria).

    (d)the RNA things is: The pre-mRNA capping pathway is perhaps the most compelling example. Green plants and animals are unique in their use of a different class of triphosphatase enzyme that also is fused to guanylyl transferase, thereby producing a multifunctional capping enzyme (CE) [18]…Although this might be attributable to an extensive gene loss from smaller fungal genomes, efforts to sample more broadly and to incorporate weighting based on genome size have not changed the result [26].

    Whether he’s correct or not is another matter, but the idea isn’t as weird as it sounds.

    http://dx.doi.org/10.1016/j.tplants.2007.08.002

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  • Suvrat Kher

    Ian-
    i don’t think T. Ryan Gregory is objecting as much to the proposed new evolutionary relationship between animals, fungi and plants as to the Discovery channel’s report that this new work would mean that fungi will have to be “demoted” and plants will have to I guess “promoted” up the perceived ladder of life.

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  • TR Gregory

    Hi Ian,

    Thanks for the detailed summary — it does sound interesting, though I am not a systematist and I would be perfectly happy with either topology for the deep nodes in the eukaryote tree.

    As Suvrat noted, my issue was with how this was reported in the media. It follows my guide perfectly, by making appeals to common misconceptions about biology. That includes describing the RNA work as though the only possibility is that fungi are not derived.

    I suppose the first question I have from a scientific perspective is: whose genomes did he look at with regard to RNA processing mechanisms? If it’s yeast vs. Arabidopsis vs. animals only, then I would have serious doubts.

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  • TR Gregory

    Ian was kind enough to send me the Stiller paper (though of course I could/should have looked it up myself!). It looks like a decent article, but looking through some of the references it cites, it does seem like a lot of the comparison is based on yeast. I’m not judging the merit of the hypothesis — I actually don’t even have that much interest in it, let alone much expertise — but any time conclusions are based on only a small sample of organisms with convenient properties, such as yeast, I am skeptical. Someone with more knowledge in plant and fungal systematics and genetic diversity could comment further, perhaps.

    In any case, the claim itself was not the point of my post. I was commenting on the Discovery Channel report. In particular, the idea that taxa can be “demoted”, that this would entail moving them away from animals on a phylogeny, and that some groups are “more highly evolved” than others.

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  • Ian

    In any case, the claim itself was not the point of my post. I was commenting on the Discovery Channel report.

    Yeah, that’s part of the problem – thanks to people like you (nah, not really, I was like that before I ever started reading blogs) I just take bad science journalism to be the norm, and try to figure out what the study actually said. Thus, I totally missed your point.

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  • John Logsdon

    To continue this thread, I have posted over at my blog.

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