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How similar is today's comb jell to its very first ancestor?

  1. Jan 2, 2019 #1
    I understand that we share a small percentage of genes with the comb jelly.

    Is it known how many genes the contemporary comb jelly would have with the very first "comb jelly" ancestor that is our ancestor too?

    Did comb jellies actually not really change much in all these years?

    Any thoughts appreciated!
     
  2. jcsd
  3. Jan 2, 2019 #2

    berkeman

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  4. Jan 2, 2019 #3
    So its last common ancestor was 65 million years ago and sounds like haven't changed much since then, as I found that it says that "genetic differences between these species were very small".

    But they also pointed out that 65 million years is quite recent, which I guess means that they are perhaps still very different from the earliest comb jelly ancestors.

    Still looking for the answer.
     
    Last edited: Jan 2, 2019
  5. Jan 2, 2019 #4

    jim mcnamara

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    First off there is no good way to know what the early comb jellies looked like, AFAIK there are no good fossils of much of any species jellies - from ~600 million years ago.

    https://www.nature.com/news/genome-reveals-comb-jellies-ancient-origin-1.12176

    This explains that comb jellies were likely the very first animals, probably came before sponges evolved. The researchers are using techniques that compare DNA with modern vertebrates and these little guys - the living ones today.
    My problem with this is you cannot assume comb jellies just stopped evolving ~600 million years ago. So, placing long extinct animals and plants in tree structures based in DNA is interesting from the standpoint of getting a handle on the history of life, but you cannot draw conclusions about what comb jellies looked like way back when. Or how they behaved - or even if that even makes sense. And just because they have cytochome-C for aerobic respiration does not tell us about all of the possible extinct variants. If we could get DNA samples from back then it would be different. All of this data mostly is used to improve cladistics. Kind of like how Ancestry.com can tell where your recent ancestors came from. They can actually go back several thousands of years.

    Cytochrome C is part of mitochondria which comb jellies do have, and so do we:
     
    Last edited: Jan 2, 2019
  6. Jan 2, 2019 #5

    jim mcnamara

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    PS: look up Edicarian this was an early period with lots of unrecognizable life forms.
    https://en.wikipedia.org/wiki/Ediacaran_biota

    The Ediacarian spans from the end of snowball Earth and the start of the Cambrian. The first multicellular "things" were alive back then. Eucaryotic single celled like existed well before snowball Earth started. (Cryogenian) . Look at the second chart in the Edicarian article and go from there.
     
    Last edited: Jan 2, 2019
  7. Jan 2, 2019 #6
    Thanks Jim, super helpful!
     
  8. Jan 3, 2019 #7

    BillTre

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    I don't know how many genes this would be, but a genome comparison of humans and ctenophores (comb jellies) should be able to answer that question.
    Since I could not find that quickly, I found this article, that says: "genes shared between bilaterians and ctenophores (7,771)" (see fig. 3).
    Bilaterians would include humans and therefore be somewhat representative of the comb jellies comparison with them.
    If humans has about 20,000 genes, then the percentage should be >50%, but could be smaller, since not all bilaterian genes will be found in humans.
    Presumably, these genes would be things involved in cell structure and function, as well as things like cell-cell communication, some of which are present in choanoflagellates and which are involved in the development of higher metazoans.

    The article also has interesting information about when specific traits like collagen, miRNAs, Hox genes, neurons, and muscle cells arose, based on the phylogeny they are using.
    Alternative phylogenies would have a different sequence of these events.
    These features are all involved (as well as molecular genome studies) in determining how the most primitive phyla that arose at the base of the metazoa (animals) are related and the order in which these metazoan traits arose.

    The commonly assumed closest outgroup to metazoans are the choanoflagellates.
    This (or actually their ancestors in the distant past) would be the group from which metazoans arose.
    This was originally based upon the great similarity of the choanoflagellates with the choanocytes of sponges (with are often considered the original metazoan), but has been confirmed by molecular studies.

    How exactly the most primitive metazoan phyla, the placozoans, ctenophores, cniderian (jellyfish, anenomes, and corals), and Xenacoelomorphs relate to each other, still seems to be in dispute since recent studies have not yet settled on a common answer.
    Some phylogenies have neurons and muscles arising independently (which seems unlikely to me) or that they were lost in some metazoan lineages. Other phylogenies have other issues.
    Personally, before I am have too much confidence in any particular hypothesis, I want to see more studies converging on a common phylogenetic hypothesis.
    This has not yet happened. The game is still afoot.

    Most Ediacaran fossils have not been related to modern groups of animals, but several of the Cambrian fossils have been.
    Molecular studies have indicated that the first animal groups arose well before the Cambrian.

    Yes, it seems that many earlier Ctenophores died out since they split from the rest of the metazoans.

    I like @berkeman's post since I did not realize there was such a diversity of extant Ctenophores.
     
  9. Jan 3, 2019 #8
    Thank you so much for all this information.

    I was partially hoping that some genetic material might have been extracted from fossils to derive a genetic comparison between the comb jelly and its ancestor.

    I guess the genes that we share with them reveal what genes were "present" back then, but the information that is not really known (yet) is: which extra not-shared genes, and how many, the ancestral com jelly would have had compared to the modern comb jelly.

    Or is it possible to "estimate" this based on the actual physical fossils and the cell components they possessed..?
    (EDIT: never mind that last comment, there just aren't any fossils out there as you said!)
     
    Last edited: Jan 3, 2019
  10. Jan 3, 2019 #9

    jim mcnamara

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    Be careful in assuming how many genes and visible were brought forward. The point I was failing to make with the Ediacarians as related to your question: If you go back far enough you lose a most of DNA in fossils, and morphology is all we have. Morphology sort of fails for Ediacarians in general:

    Those bizarre forms in fossils from then are very hard to work out, other than that they were multicellular, and we assume most were eukaryotic. So, therefore, Ctenophora and therefore mammals must have had relatives in the melange of life forms somewhere back then, but there is no irrefutable way currently known to figure that out. Educated guesses remain.

    The history of the evolution of an organism resides in the extant modern DNA. FWIW, Some biochemicals are also known to persist in ancient fossils. But not actual "missing" DNA for really old fossils like the Ediacarians. So we are left with morphology/ecology on things ~550 million years old. Ediacarians are a good example of this quandary. Bilatarians appear first in later Ediacarian sites. We are Bilateria, bilateral symmetry.

    Dinosaur pigments have been found in fossil material.
    Dinosaur feather colors based on ancient traces of biochemicals: https://news.nationalgeographic.com/news/2010/01/100127-dinosaur-feathers-colors-nature/

    Paper on Ediacarian 'Advent of Animals':
    https://www.pnas.org/content/112/16/4865 look at the graphics of fossils. Some look like annelid worms (e.g., earthworms), so does that mean they are the ancestors of earthworms? I would not care to bet the farm on it.

    BTW: the paper notes that the modern phyla first appear in the Ediacarian.
     
    Last edited: Jan 5, 2019
  11. Jan 3, 2019 #10
    Super helpful. Thank you!

    I think what has been "confusing" me is when articles and papers refer to those "first" organisms as "sponges", or "jellies", or as you pointed out, potentially even "worms", but in reality, all these names refer to contemporary organisms, and calling these ancient organisms by using the same terminology easily makes one assume that they haven't changed much since then, but in reality, that is not (necessarily) true at all.

    Thanks for clarifying that.
     
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