ZeFrank on the slime mold

August 6, 2022 • 1:45 pm

UPDATE:  I called a dicty worker and got this answer.

The solution to the “altruism” problem requires two things. First, stalks and spores are formed only when there’s a shortage of food (bacteria, usually). That means that all the genes in all of the individuals in the area will not leave copies if there’s no way to disperse those genes away from the locale of famine.

Second, dicty individuals that are more related to each other are more likely to get into the spore-forming top, but if you share ANY genes for this behavior with other individuals in the spore body, you’re still better off being part of the stalk than simply dying, for there’s still a chance that some of your genes will be in slightly related individuals that form the spores. Better to take that chance that ensure that you leave no descendants.

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ZeFrank has another biology video, this time on the slime mold (one with an amoeba life stage) Dictyostelium discoideum.  This is a strange microorganism that usually reproduces asexually, but can do so sexually. In one stage of the asexual reproduction, the cells aggregate into a slug which then turns into a stalk that produces spores that disperses genes. Some of the cells that aggregate, however, don’t get to reproduce as they form the stalk instead of the reproductive top of the stalk. It seems, in other words, like a form of altruism.

I used to know the answer to this conundrum, because a cell certainly doesn’t want to help other cells reproduce at the cost of its own reproduction.. (If they were  genetically identical it wouldn’t matter, but I don’t think they are.)  And I don’t think ZeFrank gives the solution.

I know some readers here work on “Dicty”, as they call it, so we’ll have an answer soon.

16 thoughts on “ZeFrank on the slime mold

  1. “Imagine if your instinct was to have sex, order a pizza, and then eat the delivery boy — ‘What do you mean, what kind of pizza was it, Jerry! It doesn’t matter! You’re eating the…’ Well meat lovers. No wait, vegetarian, for the irony!”

    A little hat-tip to PCC[E]?

    1. This is great in general because I re-loaded the page to see the update.

      However, I’m not sure it updated yet. Guess it takes a while longer than I do to mash buttons on the computer…

  2. I’ve always just assumed that in the normal course of events, the amebae that aggregate to form a slug are usually members of a single clone, hence genetically identical. It may be possible experimentally to produce slugs with mixed genotypes, but that would not be relevant if, in nature, mixed genotype slugs are rare.

  3. I assume the name in the lower right corner of some of the older video clips, John Bonner, refer to John Tyler Bonner (1920-2019) of Princeton University, who wrote the popular science book “The Social Amoebae: The biology of Cellular Slime Molds” and several other books and textbooks on evolution. Well worth a read if you liked the video.

  4. My knowledge of slime moulds has increased at least 1000-fold. I was delighted to learn that the ubiquitous messenger molecule cyclic AMP, (which in us is an intracellular signal with myriad effects that depend on the differentiation phenotype of the cell,) mediates the aggregation of the amebas when secreted into their extracellular environment. The source molecule is our old energy friend ATP. This is as profound a revelation as if they, like us, used Twitter: an exponentially propagating social medium.

  5. Dictyostelium was one of the earliest species to have its genome fully sequenced, largely because of its fascinating role as a bridge between uni-cellular and multi-cellular organisms. The paper is in Nature 435, 43–57 (2005) [https://doi.org/10.1038/nature03481] and it appears to be open-access.

    Full disclosure: I was a member of the Sanger Institute team that was part of the collaboration to sequence Dicty, and I’m listed among the co-authors of the paper, albeit quite a long way down the list. I provided some bioinformatics support during the genome assembly stages.

  6. Amazing video, although not yet at Attenborough’s level, I kind of find solace in his voice.
    These slime moulds\ building a stalk are a kind of multicellular organism with ‘somatic and ‘reproductive’ cells

  7. I talk about this in my evolution class. I’ve always explained that the appearance of altruism here was a matter of their sharing genes, even if they weren’t all clones from the same recent lineage. So it’s more like a case of kin selection than true altruism. But I see its a bit more “fuzzy” than that.

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