An examination of the evolution of a particular type of fruit fly discovered that in a single generation, it was able to undergo tens of thousands of genetic changes.

Scientists recently found that the "apple maggot," a pest that began plaguing growers in upstate New York in the 1850s, evolved enough in a single generation that they were able change the timing of their egg-laying cycle to match the fruiting cycle of a new host fruit for their offspring.

To do so, the fruit fly Rhagoletis pomonella underwent extensive evolution during that single generation, according to a team of biologists from Rice University, the University of Notre Dame, the University of Sheffield in Great Britain, the University of Florida and Kansas State University.

Originally the insects laid their eggs inside the fruit of the hawthorn tree. In the mid nineteenth century however, New York apples began to serve as the host for some of their eggs, in spite of the fact that the apples fruited three to four weeks earlier than the hawthorn fruit.

"Today, there are two forms of Rhagoletis pomonella in the U.S., the ancestral form that times its life cycle to the hawthorn tree and a derived form that is timed to apple trees," said Scott Egan, an evolutionary biologist at Rice. "These two forms have evolved very distinct differences and are on the path to evolving into two new species."

But because about five percent of the two populations interbreed in a given year, biologists question whether R. pomonella will ever become two different species.

The team decided to experimentally replicate the original shift in host fruits by raising flies from the ancestral population in the lab under both hawthorn-like and apple-like conditions for one generation and then measure the genetic differences in the two populations. Of particular interest to them were genetic variations called "single nucleotide polymorphisms," or SNPs.

"For the ancestral flies that had been raised for one generation on the apple cycle, we documented changes in more than 32,000 SNPs," Egan said. "Overall, we found that the genetic changes undergone by this first generation accounted for up to 70 percent of all the genetic changes that had occurred between the two populations since the 1850s."

Kansas State University's Greg Ragland, co-lead author of the study, said, "The changes observed in both experimental and natural populations of R. pomonella underscore the importance of ecological selection at early stages of divergence."