Study shows that widespread adaptation to the environment can occur in just weeks.

Consider evolution slow and gradual. This is what fruit flies do. A new report is available in ScienceUniversity of Pennsylvania researchers used a controlled field experiment in order to demonstrate that flies adapt quickly to changing environmental conditions. This was due to alterations in their genomes and a variety of physical characteristics.

The experiment lasted only four months and saw changes to 60% the flies’ genomes. This direct observation of rapid and continuous adaptation in response the environment, a phenomenon known adaptive tracking, has given biologists a new paradigm to how to think about timescales of evolution.

Paul Schmidt, a Penn biology professor and senior author of the paper, said that it was an intriguing idea, but that it was unlikely until we demonstrated it.

“What makes it so exciting is that we’re seeing evolution processes in real-time with temporal resolution,” says Seth Rudman who was a colead author of the publication. Rudman is now an assistant Professor at Washington State University.

How fast?

Evolution can happen quickly in short-lived fruit flies that are fast-reproducing. It is not clear how fast, and if multiple traits can evolve simultaneously in response to environmental changes.

Schmidt and his colleagues had previously observed that fruit flies at the beginning of the growing seasons were different from those in the late fall. This was due to differences in stress tolerance, reproductive fitness, pigmentation, and other factors. However, this research didn’t rule out that new flies could be entering the population and causing these dramatic shifts.

The team created an experimental orchard to better control the conditions of their studies. It is located on a parcel of land at Pennovation works, just a few minutes from Penn’s main campus. Schmidt’s laboratory members can use multiple enclosures to study flies under real-life conditions, including heat, rain and heat. They also keep flies out of the enclosures. Therefore, the insects found in the enclosures after an experiment are completed are direct descendants of those that were released into the enclosures at their beginning.

Checking in on evolution

The researchers started the current investigation by releasing 1000 Drosophila melanogaster In July 2014, fruit flies were found in 10 different enclosures. In July 2014, fruit flies were placed in each of the 10 enclosures. They were fed the same diets but left to their own devices. Each population had reached approximately 100,000 at the peak of the experiment.

Each month, the team removed individual insects and 2,500 eggs from each of the enclosures. Then, they analyzed each one for six physical characteristics that are governed by multiple genes.

The researchers also randomly selected 100 flies from each enclosure and sequenced their genomes together as a group during the monthly check-ins. This allowed them to take a snapshot at the evolution of allele frequencies and the variations at different points within the genome over time.

Both the physical and genomic data showed that the flies were adapting to new environments and were developing faster than anyone had ever seen.

Schmidt states, “We have seen that people are able to track environmental changes.” Schmidt says that this was not a response only to a single event such as a drought. Throughout the experiment, the populations changed and evolved throughout.

Fluctuating adaptation

Flies are usually short-lived and the time interval between each analysis was approximately one to four generations. That’s roughly ten generations in total.

Despite this, the scale of adaptation was still surprising. Over 60% of the flies’ genomes changed during the experiment. Schmidt and Rudman point out that this does not mean that evolutionary selection is acting on more of the genome. Instead, DNA is pulled along by other parts changing in a process called “genetic draft”.

What made these findings so compelling was the fact the direction of adaptation changed multiple time, swinging like an oscillator as environmental conditions changed.

Rudman comments, “It was very surprising to think that a trait can evolve over a number of weeks and then reverse direction in the next month.” “This shows adaption and selection as being dynamic. The direction of natural Selection is changing, the targets change, and they are changing very quickly.

The researchers explained that previous studies may have underestimated the rate at which adaptation occurs because they only looked at genomic changes between two distant points in time, such as A and B. This experiment was performed repeatedly and often on the same population to show what happened between the A to B toC and Bfluctuations.

Although fruit flies reproduce much faster than humans, the researchers believe their findings can be applied to other species that are longer-lived and more slowly-regenerating, such as humans.

Schmidt says that although these processes are occurring in many organisms, it’s difficult to measure them over the appropriate timescales. “So, while fruit flies are subject to seasonal changes, humans could face climate change, agriculture, and the need to eat milk. This could be a global phenomenon. It is up to us now to determine the time frame in which it is occurring.”

Rudman and Schmidt coauthored this paper with Penn’s Subhashrajpurohit, Nicolas J. Betancourt and Jinjoo Hanna, as well as Stanford University’s Sharon I. Greenblum and Susanne Tilk, Tuya Yookoyama and Dmitri I. Petrov. Rudman, Rajpurohit and Greenblum were the first authors.