Do you think evolution is a slow, gradual process? Fruit flies prove it wrong much to the annoyance of creationists!

In a new report in Science, researchers  used a controlled field experiment to show that flies rapidly adapted to shifting environmental conditions with alterations throughout their genome and in a suite of physical characteristics.

Over the course of the experiment, which lasted just four months, the researchers documented changes to 60% of the flies' genome. With this direct observation of swift and continuous adaptation in response to the environment—a phenomenon known as adaptive tracking—the biologists have established a new paradigm for how to think about the timescale of evolution.

What makes this so exciting is the temporal resolution with which we're seeing evolutionary processes in real time!

It's long been known that evolution can progress quickly in short-lived and fast-reproducing fruit flies. But exactly how fast has remained in question, specifically whether multiple traits could evolve together, continuously, in response to short-term environmental changes.

In earlier studies  researchers had seen that the fruit flies present at the beginning of the growing season were quite different from those buzzing about in the late fall in measures of stress tolerance, reproductive fitness, and even pigmentation. But that research couldn't rule out the possibility that new flies were entering the population, causing the dramatic shifts.

To more tightly control the circumstances of their studies, the scientists developed an experimental orchard. There, multiple enclosures allowed researchers  to study flies in real-life environmental conditions—cold, heat, rain, and all—while preventing flies from entering or escaping. Thus, the insects in the enclosures at the end of an experiment are known to be the direct descendants of those released into the enclosure at the study's beginning.

The researchers began the current investigation by releasing 1,000 Drosophila melanogaster fruit flies in each of 10 enclosures in July of 2014. The flies were then fed the same diets, but otherwise left to their own devices. At the experiment's peak, each population had grown to roughly 100,000 in number.

Once a month, the team removed individual flies and 2,500 eggs from each enclosure, raised them separately, then analyzed them for six different physical characteristics known to be governed by multiple genes, such as reproductive success and cold tolerance.

In addition, during each of those monthly check-ins, the researchers randomly selected 100 flies from each enclosure's population and sequenced their genomes as a pooled group. In doing so, they could get a snapshot of the changing allele frequencies—the variations in different points in the genome—over time.

The evidence from both the physical and genome data was clear: The flies were evolving, adapting to their environment, and they were doing so faster than anyone had ever measured before.

Because flies are short-lived, the time period of a handful of weeks between each analysis translated to one to four generations of flies, or roughly ten generations over the course of the whole experiment.

Even so, the magnitude of adaptation was unexpected, with more than 60% of the flies' genome evolving directly or indirectly during the experiment.

this doesn't mean evolutionary selection is acting on more than half of the genome—some DNA gets pulled along when other parts change in a process known as "genetic draft."

But what made the findings particularly compelling was that the direction of adaptation changed multiple times, swinging like a pendulum as environmental conditions changed.

To think that a trait could evolve over a certain number of weeks, and then reverse direction the following month, that was very surprising.

This paints a picture of adaption and selection being really dynamic. The direction of natural selection is changing, the targets are changing, and they're changing really quickly.

Seth M. Rudman et al, Direct observation of adaptive tracking on ecological timescales in Drosophila, Science (2022). DOI: 10.1126/science.abj7484. www.science.org/doi/10.1126/science.abj7484

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Another interesting story on evolution:

New, clearest evidence yet that humans are a dominant force driving evolution

Humans reshape the environments where they live, with cities being among the most profoundly transformed environments on Earth. New research now shows that these urban environments are altering the way life evolves.

A ground-breaking study led by evolutionary biologists  examines whether parallel evolution is occurring in cities all over the world. In findings published in the journal Science, the Global Urban Evolution Project (GLUE) analyzed data collected by 287 scientists in 160 cities in 26 countries, who sampled the white clover plant in their cities and nearby rural areas. What they found is the clearest evidence yet that humans in general, and cities specifically, are a dominant force driving the evolution of life globally. From Toronto to Tokyo, Melbourne to Munich, white clover is frequently evolving in direct response to environmental changes taking place in urban settings.

This study illustrates that the environmental conditions in cities tend to be more similar to each other than to nearby rural habitats.

Not only were researchers able to observe global adaptation to cities, they identified the genetic basis of that adaptation and the environmental drivers of evolution. White clover produces hydrogen cyanide as both a defense mechanism against herbivores and to increase its tolerance to water stress, and GLUE found that clover growing in cities typically produce less of it than clover in neighboring rural areas due to repeated adaptation to urban environments.

It is the changes in the presence of herbivores and water stress in cities that is pushing white clover to adapt differently than their rural counterparts.

That finding holds true for cities across various climates, and the implications reach far beyond the humble clover plant.

James S. Santangelo, Global urban environmental change drives adaptation in white clover, Science (2022). DOI: 10.1126/science.abk0989. www.science.org/doi/10.1126/science.abk0989