Fruit fly evolution shifted with the seasons during a four-month outdoor experiment in Philadelphia in 2014, researchers reported in a study published in 2022. Changes affected more than 60% of the flies’ genome directly or indirectly, though that does not mean natural selection acted on every affected region.
Key Takeaways
- The experiment followed enclosed fruit fly populations from July to November 2014.
- Some genetic changes may have been carried along by selection on nearby DNA rather than selected directly.
- The researchers observed traits changing direction over time, suggesting adaptation could be missed by sampling only at the beginning and end of a season.
How researchers tracked fruit fly evolution
Scientists introduced 1,000 Drosophila melanogaster fruit flies into 10 outdoor shelters at Pennovation Works. The shelters exposed the flies to weather while preventing outside flies from entering the populations, which grew to around 100,000.
Each month, researchers collected eggs and flies from each shelter and examined six physical characteristics, including reproductive success and cold resistance. They also randomly selected 100 flies from each shelter for genome sequencing.
The experiment ended at the first hard frost on November 7, 2014. Because generations overlapped, the researchers estimated that roughly 10 to 12 generations passed during the study.
Why genetic changes reversed
The researchers found that the direction of adaptation changed several times. Co-lead author Seth Rudman said it was surprising to see a trait evolve in one direction for a few weeks and then move the other way the following month.
Some DNA changes reflected genetic draft: regions were carried along with changes in nearby sections. The study therefore does not establish that selection acted directly on more than half of the genome.
The findings were published in Science in 2022. Whether similar patterns extend to longer-lived, slower-reproducing species, including humans, remains a hypothesis.
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