Evolution News stasis

Sponges vs. jellies: Comb jellies still the “oldest” complex life form, researchers say

Spread the love
comb jellyfish/kondratuk, Fotolia

Spotted at about 600 million years ago. From ScienceDaily:

One of the longest-running controversies in evolutionary biology has been, ‘What was the oldest branch of the animal family tree?’ Was it the sponges, as had long been thought, or was it the delicate marine predators called comb jellies? A powerful new method has been devised to settle contentious phylogenetic tree-of-life issues like this and it comes down squarely on the side of comb jellies.

For nearly a century, scientists organized the animal family tree based in large part on their judgement of the relative complexity of various organisms. Because of their comparative simplicity, sponges were considered to be the earliest members of the animal lineage. This paradigm began to shift when the revolution in genomics began providing vast quantities of information about the DNA of an increasing number of species. Evolutionary biologists started to apply this wealth of information to refine and redefine evolutionary relationships, creating a new field called phylogenomics. In most cases, the DNA data helped clarify these relationships. In a number of instances, however, it gave rise to controversies that intensified as more and more data accumulated.

Comb jellies took the lead in 2008 but sponges struck back in 2017.

It seemed so obvious: Sponges are simpler. However, some data offered “apparently irreconcilable” differences:

The researchers determined how much support each gene provides to one hypothesis (comb-jellies first) over another (sponges first). They labeled the resulting difference a “phylogenetic signal.” The correct hypothesis is the one that the phylogenetic signals from the most genes consistently favor.

In this fashion, they determined that comb jellies have considerably more genes which support their “first to diverge” status in the animal lineage than do sponges. Paper. (paywall) – Xing-Xing Shen, Chris Todd Hittinger, Antonis Rokas. Contentious relationships in phylogenomic studies can be driven by a handful of genes. Nature Ecology & Evolution, 2017; 1: 0126 DOI: 10.1038/s41559-017-0126 More.

[comment]

See also: Sponges back in the ring with comb jellies for “oldest” title fight

Comb jelly files: Complex features do not each emerge once

Comb jelly DNA sequence offers “unintuitive facts” about evolution…

and

Researchers: The sponge is the oldest animal phylum after all (2015)

Follow UD News at Twitter!

4 Replies to “Sponges vs. jellies: Comb jellies still the “oldest” complex life form, researchers say

  1. 1
    mahuna says:

    OK, so these 2 “animals” are closely related and their shared parent species is…??

  2. 2
    Armand Jacks says:

    Mahuna:

    OK, so these 2 “animals” are closely related and their shared parent species is…??

    KF? 🙂

  3. 3
    Dionisio says:

    Despite their soft, gelatinous bodies, fossils thought to represent ctenophores, apparently with no tentacles but many more comb-rows than modern forms, have been found in lagerstätten as far back as the early Cambrian, about 515 million years ago. The position of the ctenophores in the evolutionary family tree of animals has long been debated, and the majority view at present, based on molecular phylogenetics, is that cnidarians and bilaterians are more closely related to each other than either is to ctenophores. A recent molecular phylogenetics analysis concluded that the common ancestor of all modern ctenophores was cydippid-like, and that all the modern groups appeared relatively recently, probably after the Cretaceous–Paleogene extinction event 66 million years ago. Evidence accumulating since the 1980s indicates that the “cydippids” are not monophyletic, in other words do not include all and only the descendants of a single common ancestor, because all the other traditional ctenophore groups are descendants of various cydippids.
    https://en.wikipedia.org/wiki/Ctenophora

    How does the cydippids develop?
    How can the cydippids development process turn into the crenophore development process?
    IOW, what changes are required in the cydippids development process in order to get the ctenophore development process?
    Development(ctenophore) = Development(cydippids) + Delta(ctenophore)

    https://en.wikipedia.org/wiki/Cydippida

  4. 4
    polistra says:

    I’ve been thinking about this in terms of language. “Simplest is oldest” seems logical but it doesn’t apply to language and it doesn’t apply to genetics. “Primitive” languages are ferociously complex. As a language spreads out to different groups of people with different requirements, each branch simplifies in a different way. Some lose noun cases, some lose tones, some lose verb forms. Occasionally a new superficial complexity may develop, just as a new decoration or coloration may appear on animals; but the overall structure always wants to get simpler.

    Where else does this rule apply? Governments. The 1787 constitution had a wonderfully organic setup of boundaries and layers and self-governing modules. Now we’re down to one module with no boundaries.

    Music. Bach to rap.

    Art. Rembrandt to elephant dung.

Leave a Reply