Living Inside Someone Else’s House

Photos from UAB in Antarctica group on Flickr, related to this post
By Chuck
Posted on 04/03/07

If something was trying to eat you and you couldn’t get up and run away and you couldn’t fight back physically, what would you do? For some organisms, the answer is to grow and reproduce faster than the things that are trying to eat you usually can eat you. So you “win” by growing fast and leaving offspring while you can.

For many of the large organisms we work on, the answer to that question is to make yourself taste bad using chemical defenses so that the other organism does not want to eat you. Those are the standard “answers.”

But, there is another way. If you are small and really skinny, perhaps you could sneak into someone else’s chemically defended body and slide your cells in between theirs.

That is what we think is a very important strategy for small macroalgae here. If “small” and “macroalgae” seems like an oxymoron, it may well be. But in this context, “macroalgae” means multi-cellular and “macro” means something you can see with your eye, at least some of the time.

You’ve read other posts about how important we think small grazing animals, particularly amphipods, are in structuring the communities here. As Craig’s amphipod gut analyses have been confirming, they like to eat small, filamentous macroalgae.

What does “filamentous” mean? A filament is essentially a string. Think of a string of beads in which every bead was a cell. That is a filament. Sometimes a filamentous alga can be more than one cell across (think several strings of beads stuck together), but in this context, not very many cells across.

As first pointed out in the scientific literature by my colleague Akira Peters, there are very few filamentous macroalgae in Antarctica that grow on rocks, animals, or the outside of large algae. In fact, very, very few. But it appears that there are a lot of filamentous macroalgae that live endophytically.

“Endo” means “within” and “phytically” refers to a plant or alga. So an endophyte literally lives within the body (for an alga, the “thallus”) of another plant or alga. I have seen a whole lot of large algae with small, filamentous macroalgae growing within them here. Far more here than I have seen anywhere else I have been.

Filamentous algae are usually considered “simple” and there are few examples of them defending themselves using chemistry. Mostly they are thought of as growing and reproducing faster than the herbivores can keep up with them. But few places in the world have as many amphipods (or similar small herbivores) specializing on small algae.

As Dr. Peters first hypothesized, we suspect that the reason filamentous endophytes are so common while filamentous algae are otherwise so rare here is because the endophytes are effectively hiding from amphipods within the thalli of the larger, chemically defended algae.

But chemical defenses can have multiple roles. The same chemicals that make something taste bad to a herbivore can also make it chemically inhospitable to an endophyte. So if you are going to live inside another alga, you’d better be able to tolerate its defenses.

Getting all of this back to our studies this season, we want to have an understanding of how common these endophytes are and how specific they are to particular macroalgae. Dr. Peters’ work suggested that particular species of endophytes live only in particular macroalgae, but he didn’t’ have a big enough sample to say that for sure. We hypothesize that he is correct, and that the reason he is correct is because the endophytes have to be able to tolerate their hosts defenses against other endophytes and herbivores.

To test that hypothesis, we need data on how common and how host-species-specific these endophytes are. So my main data-gathering role this year is to do that survey.

I have been collecting individuals of the larger and more common macroalgae from multiple sites around Palmer for the past few weeks and will continue this for the rest of the season. I bring them into the lab and then weigh an measure them. For the flat algae, I cut disks of known diameter (essentially with a fancy “cookie cutter”) and then weigh those. Knowing the weight of the whole plant, and the weight of the disks, with the flat algae I can easily estimate the total surface area of the plant available for the endophytes to lie under.

Next I carefully examine the plant in the light and look for shading from things living within it. I have to sort through small microalgae called diatoms that often live on the surface. But using my eye, and then microscopes of increasing resolving power I can pin down what has endophytes and what does not. All this goes into my data book.

I also have been cutting disks of the larger algae with the endophytes within them in order to have cultures of the endophytes to work with once we get back to UAB. In addition, I am preserving disks for DNA analysis to help determine what endophytes are within.

The problem with these simple endophytes is that there is not much to look at to help you recognize one species from another. So genetic (DNA) analyses are very important in helping us with that.

Maggie spent a lot of time in the lab at UAB before we came down working out these DNA analysis techniques. A lot of her time between this season and next will be looking at what we have preserved in the disks and what grows out of the culture.

All this is a work in progress. But so far, it looks like indeed many species of these “simple” algae are not so simple at all. At least, they are very good at playing hide and seek with the amphipods and other herbivores that would like to eat them if they could!

Comments

  1. Re: Living Inside Someone Else’s House
    Posted by akira peters on 04/05/07

    Dear Chuck,
    I am pleased to see my speculations on the functioning of the Antarctic phytobenthic communities have been translated by Chuck into real hypotheses and are being tested. Here are three comments.
    1. Years ago I tried to cultivate filamentous endophytes growing in different Antarctic macroalgae. This worked well for brown endophytes but failed for the green endophytes in red algae, e.g. in Curdiea racovitzae. Maggie and Chuck make sure you preserve enough material of such infected red macroalgae to get DNA out of the mixture host-endophyte for PCR amplification with green algal-specific primers.
    2. According to Bob Wilce, small free-living or epiphytic algae are also rare in the Arctic region; if this is true, and if endophytes are present there as well, the phenomenon studied by Chuck may be common to very cold regions.
    3. One of the endophyte species I isolated in 1997-8 from Antarctica was Ascoseirophila violodora. It was isolated from the interior of the large brown macroalga Ascoseira mirabilis. Ascoseira is well defended against grazing by polyphenols. I made two independent isolates of Ascoseirophila, both grew well in culture, and both produced a strong sweet odor, beta-ionone, the main odor of violets - thus the name. However, in my cultures these endophyte isolates have after several months ceased to produce beta-ionone. I don't know whether the beta-ionone is involved in the interaction between host and endophyte but possibly a host stimulus is needed to stimulate its production in the endophyte.
    Best wishes Maggie and Chuck,
    Akira

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