Evolution: a different view with loss of traits; jellyfish (Introduction)

by David Turell , Monday, December 03, 2018, 19:14 (2181 days ago) @ David Turell

Jellyfish metamorphasize and use old genes to do it:

https://phys.org/news/2018-12-jellyfish-genome-reveals-ancient-complex.html

"Jellyfish undergo an amazing metamorphosis, from tiny polyps growing on the seafloor to swimming medusae with stinging tentacles. This shape-shifting has served them well, shepherding jellyfish through more than 500 million years of mass extinctions on Earth.

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"'Whatever they're doing has really worked for them," said David Gold, an assistant professor of paleobiology in the UC Davis College of Letters and Science.

"The first in-depth look at the genome of a jellyfish—the moon jelly Aurelia aurita—reveals the origins of this successful survival strategy. The Aurelia genome, published online Dec. 3 in the journal Nature Ecology and Evolution, indicates early jellyfish recycled existing genes to morph from polyp to medusa. The results suggest animals can radiate into new niches and forms fairly easily.

"'These findings provide further evidence that evolution doesn't necessarily make the genetic code more complex," said Gold, a lead researcher on the genome study. "Jellyfish can build a big, complex life history using many of the same genes found in simpler animals." (my bold)

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"At some point in their evolution, jellyfish gained the ability to transition from a stationary polyp to a swimming medusa. The transition involves major changes in the jellyfish nervous system, muscles and weaponry, aka the stinging cells called cnidocytes. To accomplish this, the medusa life stage often co-opts existing developmental gene networks and cell types present in polyps, the researchers found. In addition, Aurelia appears to pattern its different life stages using many of the same genes found in animals such as fruit flies and humans, the study reports. (all of these animals share a common ancestor, albeit an ancient one.)

"There is a second, more controversial explanation for what the scientists found in the jellyfish genome. Perhaps the similarities between the moon jellyfish genome and "higher" animals demonstrates that the Cnidaria originally had a medusa life stage, which animals like corals and sea anemones lost."

Comment: Note my bold. Advances in evolution can use old genes and not more complexity of genes! Devolution is real.