Many crustaceans, including lobster, crabs, and barnacles, have a cape-like shell protruding from the head that can serve various roles, such as a little cave for storing eggs, or a protective shield to keep gills moist.
August 1, 2022
Many crustaceans, including lobster, crabs, and barnacles, have a cape-like shell protruding from the head that can serve various roles, such as a little cave for storing eggs, or a protective shield to keep gills moist.
This shell (carapace), it’s been proposed, didn’t evolve from any similar structure in the crustacean ancestor, but appeared de novo (or out of the blue) through somewhat random co-option of the genes that also specify insect wings.
However, in a new study from the Marine Biological Laboratory (MBL), Research Associate Heather Bruce and Director Nipam Patel provide evidence for an alternate view: The carapace, along with other plate-like structures in arthropods (crustaceans, insects, arachnids, and myriapods) all evolved from a lateral leg lobe in a common ancestor.
This evidence buttresses their proposal for a new concept of how novel structures evolve—one that suggests that they aren’t so novel, after all. The study, on the carapace of the crustacean Daphnia, appears online in Current Biology.
“How novel structures arise is a central question in evolution,” Bruce says. “The prevailing idea, called gene co-option, is that genes that are functioning in one context, say to make insect wings, end up 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.
