A new study, published in the April 20th issue of Nature, has pinpointed the genetic mechanism responsible for the evolution of spots on fruit fly wings. The new work provides an example of convergent evolution—when two distinct species evolve similar traits in different environments with similar attributes.
Benjamin Prud'homme, a post-doc at the Howard Hughes Medical Institute, part of the University of Wisconsin-Madison, was able to isolate the portion of DNA responsible for spotted wings to within 10 base pairs; the fruit fly genome contains some 180 million pairs of nucleotides.
"[The finding] illuminates some of the fundamental genetic mechanisms and principles driving evolution," Prud'homme said in relation to his research.
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Prud'homme discovered that the cis-regulatory element (or on/off switch) for a gene that controls generation of spots is not the same in all observed fly species. In other words, different species developed separate genetic mechanisms for their wing spots.
This is a textbook case of convergent evolution and, thanks to this new research, we now know exactly what region of the fly genome mutated to cause the evolutionary change in wing coloring.
The task of sifting through such a massive genome was alleviated by the selection of fruit fly species that tended to be very similar genetically—the six species studied in Prud'homme's work were about as similar to one another as humans are to apes, he says. The presence or absence of wing spots on males of the species was the most notable variation between them. In some cases, as much as 92% of the genomes compared were completely identical.
The close similarity between most of the species chosen for analysis allowed the researchers to quickly isolate the genetic material responsible for spotted wings.
"We've pinned it down to just a few [base pairs of DNA]," said Sean Carroll, an investigator at the Hughes Institute and a coauthor of this study, along with Prud'homme.
Patricia Wittkopp, who studies the genetic mechanisms behind pigment variations in fruit flies at the University of Michigan, emphasized the importance of Prud'homme's research as evidence for convergent evolution.
"It provides empirical evidence of phenomena that were previously relegated to the realm of speculation," she said.