In an advance online publication February 6 by Nature of a paper scheduled to appear in Nature, the scientists show how mutations in regulatory genes that guide the embryonic development of crustaceans and fruit flies allowed aquatic crustacean-like arthropods, with limbs on every segment of their bodies, to evolve 400 million years ago into a radically different body plan: the terrestrial six-legged insects.
The achievement is a landmark in evolutionary biology, not only because it shows how new animal body plans could arise from a simple genetic mutation, but because it effectively answers a major criticism creationists had long leveled against evolution-the absence of a genetic mechanism that could permit animals to introduce radical new body designs.
"The problem for a long time has been over this issue of macroevolution," says William McGinnis, a professor in UCSD's Division of Biology who headed the study. "How can evolution possibly introduce big changes into an animal's body shape and still generate a living animal? Creationists have argued that any big jump would result in a dead animal that wouldn't be able to perpetuate itself. And until now, no one's been to demonstrate how you could do that at the genetic level with specific instructions in the genome."
The UCSD team, which included Matthew Ronshaugen and Nadine McGinnis, showed in its experiments that this could be accomplished with relatively simple mutations in a class of regulatory genes, known as Hox, that act as master switches by turning on and off other genes during embryonic development. Using laboratory fruit flies and a crustacean known as Artemia, or brine shrimp, the scientists showed how modifications in the Hox gene Ubx-which suppresses 100 percent of
Contact: Kim McDonald
University of California - San Diego