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Whad’ya Know About Protists?

My advisor has recently got me listening to Whad’ya Know. My first reaction: It’s like Wait Wait…Don’t Tell Me! Only not as funny, not as interesting, and not as good. I’ve been downloading the podcasts for the past couple of weeks, and I’m not sure whether I’ll keep subscribing in iTunes.

I’m only bringing this up because last week’s episode contained a very egregious example of someone knowing just enough biology to get themselves in trouble. The sad part was that the person should have known better. Why? She teaches biology at the university level.

What happened? At the midpoint of the first hour of the show, Michael Feldman conducted the quiz. The in-house participant was Deb, a grasslands ecologist. Deb was asked about the diet of early Americans, which turned out to be seaweed. Deb then pointed out that seaweed is not a plant. Huh? Then she said it’s algae, which is a protist. Really? Deb doth protist too much, methinks.

It’s really sad to watch Deb struggle to display her out-dated understanding of eukaryotic taxonomy. It’s especially disconcerting because she’s extremely proud of her knowledge that eukaryotes (a term she does not use) are divided into four kingdoms — animals, plants, fungi, and protists. And she requires her students to know this. That is, she requires her students to gain an incorrect understanding of eukaryotic evolution.

First off, seaweed is a plant. It’s just not a land plant. The green algae, of which seaweed is a member (one of the few things Deb got right), are aquatic plants. They have no vascular system for transporting water and nutrients because they can absorb those from the surrounding water. The water also provides them with support. Algae also have no roots, no seeds, and no fruits. As plants began to colonize land, they evolved adaptations to the terrestrial environments they encountered. First, came a waxy cuticle to prevent water-loss. Then, they evolved vasculature (xylem and phloem) to transport water and nutrients to and from the roots and leaves. After that came pollen and seeds. The pollen allows individuals to fertilize each other without needing water to transport the male gametes. The seeds provide protection for the developing embryo of the plant. Flowering plants, the largest extant radiation of plants, also evolved flowers and fruits to aid in reproduction. See here for more on the evolution of land plants.

But what about that outdated misnomer, protist? If, as Deb claims, anything eukaryote that’s not an animal, fungus, or land plant, then nearly every eukaryote is a protist. That’s because the majority of eukaryotes don’t fall into one of those three small taxa.

i-5feb4cbd88250bf87fba504db8ff9f8c-Eukaryote_tree.jpg

Land plants make up a small portion of the plant group (shown in green in the top-left of the figure). Many seaweeds are green algae, a close relative of land plants (close in the scope of this tree). Animals are also a single lineage on this tree, highlighted in a red box in the bottom-right. And fungi, the most diverse of the three non-protist taxa, are made up of a few of the lineages closely related to animals in the Opisthokont clade. For more on this topic, see this post on the eukaryotic phylogeny and this article.

Everything else that I didn’t just describe would be classified as a protist according to Deb. That’s all the Excavates, Rhizaria, Chromalveolates, red algae, and green algae. Protists also make up a large portion of the Unikonts, the group containing animals and fungi. You’re probably asking, the whats? Exactly. Much of those organisms are single-celled amoeba-like critters. They’re not worthy of any sophisticated, evolutionarily-accurate taxonomy, and they get thrown in the meaning-less grab-bag known as “protists”.

What’s wrong with that taxonomic strategy? First, it does not reflect the evolutionary relationships of the organisms. Protist is a paraphyletic taxon — essentially, a group of organisms that excludes some organisms within that evolutionary group (like including reptiles to the exclusion of birds). Also, understanding the true evolutionary relationships is essential for studying the biology of these organisms. For example, the “protists” that are closely related to animals help us understand how animals evolved from single-celled organisms. Anyone knowledgeable in eukaryote systematics does not use the term “protist”, except to point out that it is incorrect.

I would hope that Deb, a woman in charge of teaching college students about evolutionary biology, would realize that protist is a meaningless classification. No contemporary introductory biology course worth anything uses that classification scheme. The taxon protist only still lingers because of its historical use. Let’s hope that it does not linger much longer.

Comments

  1. #1 Jim Thomerson
    May 20, 2008

    I bet you would be more upset if you survey how the matter is treated in the half-dozen most widely adopted introductory biology textbooks. Did I miss something here? Indians living in grasslands lived on seaweed?

    Many years ago, in the 60′s, we instituted a three part core course: part one was “wee beasties”; viruses, prokaryotes and protista. The second course was plants, the third animals. This did not work well and has been modified ad infinitum to the present day.

  2. #2 Rev Matt
    May 20, 2008

    The main problem with Whadya Know is it’s too long. Like much of SNL, it would be much funnier if it were half as long.

    Peter Sagal, on the other hand, drives me crazy with the phrase “True fact.” But is otherwise brilliant.

  3. #3 Becca
    May 20, 2008

    Kingdoms are so passe. Even the clades you have there (while highly interesting) are ridiculous in the level of implied eukaryote-centricity. It’s all about the domains, obviously.

    In all seriousness, I was certainly taught the kingdom system; but no one ever said it was particularly informative for evolutionary relationships. It is a way of categorizing things that has some historical relevance, that’s about it. But I think that it’s perfectly valid to point out that seaweed is more similar to single-celled algaes than to a potato- and that is what categorizing them together (as Deb did) achieves.
    I know cladistics has a lot to offer (that diagram is such a totally more informative way of seeing the relationships of apicomplexa to everything else- so that’s really useful for me!). But you are coming across as very pedantic, and a little snobbish. We all have pet peeves about how terminology is (mis)used in our fields, I’m assuming this just hit a nerve in that sort of fashion.

  4. #4 Jacob
    May 20, 2008

    Good points. If you want to be cladistically correct, “seaweed” is a polyphyletic taxon. So you can’t really say “seaweed is a plant.” Some seaweeds are plants, while others, including some of the species found at the archeological site, are not (e.g. Sargassum and Macrocystis are Phaeophytes and therefore Chromalveolates according to your phylogeny). That still doesn’t make “protists” a valid group, though.

  5. #5 RPM
    May 20, 2008

    Becca, yes, Deb had a valid point that some seaweeds are more similar to single-celled algae than they are to land plants. But she also stated that seaweeds are protists, like amoebas. That really bothered me.

  6. #6 Joe Dunckley
    May 21, 2008

    I believe protists are still on the A-level biology curriculum in the UK — I remember being introduced to them seven years ago, anyway (followed by the first year university microbiology lecturer having to explain to everyone why what they had learned belonged in the 18th century).

    When I worked in the US I’d listen to a lot of NPR, as it was the least appalling thing available on the radio. If you’re after a bit of real radio comedy, try some of this:

    http://www.bbc.co.uk/radio4/comedy/
    http://www.bbc.co.uk/bbc7/comedy/index.shtml?Today

  7. #7 Frank Anderson
    May 21, 2008

    I find Whad’ya Know exquisitely annoying and unfunny. Unfortunately, either the programmers of my local NPR affiliate love it, or it’s really cheap, or both…

    Wait Wait Don’t Tell Me… has its moments, though some of the panel members find themselves to be much amusing than I do.

  8. #8 moneduloides
    May 24, 2008

    Not to make the issue appear less serious than it is, but this question of classification, although an important one, is far from the most horrible perversions students encounter in their undergraduate education in the life sciences. I, personally, had the privilege of taking my biology intro course from a professor who equivocated constantly on the legitimacy of evolution. It was pretty annoying.

  9. #9 Jonathan Eisen
    May 26, 2008

    The most common argument I hear for why terms like protist should be kept around is that it is easier to use it that to say what you mean. Yes, that is right, laziness is better than accuracy. Bizarre argument given that the term protist is usually used in the context of a litany of jargon that would confuse just about anyone. I agree with you. Lets do away with using protist. If you mean single celled eukaryote, just say it.

  10. #10 Major Transition
    May 27, 2008

    “Seaweed” and “algae” are also unfortunate terms. Both are polyphyletic and used in confusing ways by both scientists and non-scientists. I once had to explain to an environmental biologist that cyanobacteria are better thought of as photosynthetic bacteria than as algae.

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