Spotting Evolution On The Wing

By Roland Piquepaille

What is responsible for the evolution of forms and shapes of living organisms? Is this our genes or the DNA mechanisms which control where genes are used in the making of the animal's body? Scientists from the University of Wisconsin-Madison have found the answer by studying the various spots on the wings of a common fruit fly. In this article, they explain that molecular switches control where the pigmentation is deployed. Common genes are controlled to produce an endless array of patterns, decoration and body architecture found in animals. And it is almost certain that these molecular switches are at work in other animals, including humans. What is even more fascinating is how it works. According to the researchers, evolution is a combination of chance and ecological necessity, which selects those things that are going to be kept. It means that animals' features are just accidents, but accidents that are preserved because they confer some kind of advantage. Read more...

By analyzing the genetic origin of a modest spot on a fruit fly wing, Howard Hughes Medical Institute (HHMI) researchers have discovered a molecular mechanism that explains, in part, how new patterns can evolve. The secret appears to be specific segments of DNA that orchestrate where proteins are used in the construction of an insect's body.

The researchers chose to study the evolution of the wing spot on the fruit fly because it is a simple trait with a well-understood evolutionary history. While ancient fruit fly species lack the spots, said HHMI investigator Sean B. Carroll, some species that evolved later have developed them under the pressure of sexual selection. The wing spots offer a survival advantage to males, who depend on the decorations to "impress" females to choose them in the mating process.

Like butterflies, different species of fruit flies decorate their wings with a great diversity of spots and patterns. Digging deep into a single gene that produce pigmentation in the flies, a group led by UW-Madison biologist Sean Carroll has found the molecular switches that control where the pigmentation is deployed. The finding explains how common genes can be controlled to produce the seemingly endless array of patterns, decoration and body architecture found in animals. (Credit for photo and caption: Nicolas Gompel and Benjamin Prud'homme, University of Wisconsin-Madison)

You'll find other pictures on this page which also contains a link to a short movie where you can see "the male fruit fly showing off his wing spots in an effort to get the attention of the ladies." (QuickTime format, 35 seconds, 10.1 MB).

The research work has been published by Nature on February 3, 2005 under the name "Chance caught on the wing: cis-regulatory evolution and the origin of pigment patterns in Drosophila" (Vol. 433, No. 7025, Pages 481 - 487). Here is a link to the abstract.

The gain, loss or modification of morphological traits is generally associated with changes in gene regulation during development. However, the molecular bases underlying these evolutionary changes have remained elusive. Here we identify one of the molecular mechanisms that contributes to the evolutionary gain of a male-specific wing pigmentation spot in Drosophila biarmipes, a species closely related to Drosophila melanogaster. We show that the evolution of this spot involved modifications of an ancestral cis-regulatory element of the yellow pigmentation gene. This element has gained multiple binding sites for transcription factors that are deeply conserved components of the regulatory landscape controlling wing development, including the selector protein Engrailed. The evolutionary stability of components of regulatory landscapes, which can be co-opted by chance mutations in cis-regulatory elements, might explain the repeated evolution of similar morphological patterns, such as wing pigmentation patterns in flies.

Here are few more resources if you're interested by this findings.

• Sean Carroll's lab
  
• Scientists find portal to how animals evolve
  An article from the University of Wisconsin-Madison
  
• A news release from the University of Wisconsin-Madison
  

Sources: Howard Hughes Medical Institute, February 4, 2005, and various websites

Related stories can be found in the following categories.

• DNA
  
• Genetics
  
• Nature
  
• Science