Genome and evolvability: going in reverse (Introduction)

by David Turell , Friday, June 21, 2024, 18:26 (155 days ago) @ David Turell

A salmon parasite is a remanent of a jelly fish:

https://www.sciencealert.com/this-is-the-first-animal-ever-found-that-doesnt-need-oxyge...

"In 2020, scientists discovered a jellyfish-like parasite that doesn't have a mitochondrial genome – the first multicellular organism ever found with such an absence. That means it doesn't breathe; in fact, it lives its life completely free of oxygen dependency.

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"...a team of researchers led by Dayana Yahalomi of Tel Aviv University in Israel decided to take another look at a common salmon parasite called Henneguya salminicola.

"It's a cnidarian, belonging to the same phylum as corals, jellyfish, and anemones. Although the cysts it creates in the fish's flesh are unsightly, the parasites are not harmful, and will live with the salmon for its entire life cycle.

"Tucked away inside its host, the tiny cnidarian can survive quite hypoxic conditions. But exactly how it does so is difficult to know without looking at the creature's DNA – so that's what the researchers did.

"They used deep sequencing and fluorescence microscopy to conduct a close study of H. salminicola, and found that it had lost its mitochondrial genome. In addition, it also lost the capacity for aerobic respiration, and almost all of the nuclear genes involved in transcribing and replicating mitochondria.

"Like the single-celled organisms, it had evolved mitochondria-related organelles, but these are unusual too – they have folds in the inner membrane not usually seen.

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"These results showed that here, at last, was a multicellular organism that doesn't need oxygen to survive.

"While H. salminicola is still something of a mystery, the loss is pretty consistent with an overall trend in these creatures – one of genetic simplification. Over many, many years, they basically devolved from a free-living jellyfish ancestor into the much more simple parasite we see today.

"They've lost most of the original jellyfish genome, but retained – oddly – a complex structure resembling jellyfish stinging cells. They don't use these to sting, but to cling to their hosts: an evolutionary adaptation from the free-living jellyfish's needs to the parasite's. You can see them in the image above – they're the things that look like eyes.

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"'Our discovery confirms that adaptation to an anaerobic environment is not unique to single-celled eukaryotes, but has also evolved in a multicellular, parasitic animal," the researchers explained in their paper, published in February 2020."

Comment: sitting in a comfy-cozy host who supplies everything, no wonder the jelly fish shucked off many of the responsibilities of survival. Deleting DNA is a form of editing DNA but is simpler than creating DNA as bacteria do. My guess is the jelly fish, themselves, did the adaptation over time, no designer needed.