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Science And Nature

What’s new beneath the sun? Researchers offer another take on how ‘novel’ structures evolve

What's new under the sun? Offering an alternate view on how “novel” structures evolve
The freshwater crustacean Daphnia (water flea) is really a common research organism in ecology, toxicology, evolutionary developmental biology, along with other fields. Credit: Proyecto Agua

Many crustaceans, including lobster, crabs, and barnacles, have a cape-like shell protruding from the top that may serve various roles, like a little cave for storing eggs, or perhaps a protective shield to help keep gills moist.

This shell (carapace), it has been proposed, didn’t evolve from any similar structure in the crustacean ancestor, but appeared de novo (or out of nowhere) through somewhat random co-option of the genes that also specify .

However, in a fresh study from the Marine Biological Laboratory (MBL), Research Associate Heather Bruce and Director Nipam Patel provide evidence for another view: The carapace, and also other plate-like structures in arthropods (crustaceans, insects, arachnids, and myriapods) all evolved from the lateral leg lobe in a .

This evidence buttresses their proposal for a fresh idea of how novel structures evolveone that shows that they aren’t so novel, in the end. The analysis, on the carapace of the crustacean Daphnia, appears online in Current Biology.

“How novel structures arise is really a central question in evolution,” Bruce says. “The prevailing idea, called gene co-option, is that genes which are functioning in a single context, tell make insect wings, result in an unrelated context, where they make, say, a carapace,” says Bruce. “But here we show that the Daphnia carapace didn’t just pop out of nowhere.”

Rather, they propose the ancestral, plate-like leg lobe that evolved into both and the carapace was likely within the ancestor of most living arthropods. But as the wing and carapace look so not the same as this ancestral plate, and from other plates in neighboring arthropod lineages, no-one realized they were yet thing.

“We have been starting to recognize that structures that don’t look anything alikewings, carapaces, tergal platesare actually homologous,” Bruce says. “That suggests they will have an individual origin that’s a lot more ancient than anyone could have thought, in the past in the Cambrian period, [500 million] years back.”

It had been there all along (cryptic persistence)

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