When faced with the threat of predation, animals adapt surprisingly fast.

According to a new study, water fleas can enact evolutionary changes within just two generations.

Scientists sequenced the genes of water flea generations spanning 20 years, identifying evolutionary changes before, during and after exposure to predators.

The sequencing data -- published Wednesday in the journal Nature Communications -- revealed the remarkable evolutionary power of standing genetic variation.

"Standing genetic variation is the genetic diversity that is at a given moment 'present' in the population," lead author Anurag Chaturvedi told UPI in an email.

"It does not need to come from immigrants -- it is just present in the population," said Chaturvedi, a bioscientist at the University of Birmingham in Britain.

The genetic variety present within a population represents that population's evolutionary potential. The more diversity, the better the odds of a population possessing the genetic tools for adaptation and survival.

Scientists were surprised by the water flea's ability to alter traits and behavior.

"Water fleas are exceptional models to understand evolution," study co-author Luisa Orsini, an associate professor at Birmingham, told UPI.

"They can reveal molecular pathways and functions altered by long-term perturbations of natural environments. Using functional similarities among species, we can learn if the same functions are altered in other species, including humans," Orsini said.

Water fleas are unique in that they produce dormant stages, like the seeds of plants, that remain viable for decades, even centuries. These dormant stages allow scientists to travel backwards on the evolutionary timeline.

"Because sediment layers of lakes are layered, it allows one to hatch animals that lived in nature decades ago," Chaturvedi said. "Using this so-called 'resurrection ecology' approach, we can thus reconstruct evolution as it happened in nature."

For their experiments, Chaturvedi and company retrieved dormant water flea eggs from the sediment of a fish farm pond.

Scientists sourced eggs from several different sediment layers, revealing the population's genome before, during and after exposure to predation from fish.

Though sequencing data showed the water fleas used just 3 percent of their genome to engineer physiological changes -- 300 genes -- the findings suggest the population's standing genetic variation allowed for significant adaptability.

To see the population's genetic variety, researchers sequenced the genomes of water flea populations in nearby bodies of water. They found they could acquire the necessary genetic variety by randomly sampling just five clones from any one population.

"So all this variation that allows such rapid evolution requires only a few immigrants and not hundreds of years to 'accumulate,'" Chaturvedi said.

Genetic diversity isn't always so easy to come by, researchers say. Species must be able to maintain large populations to ensure that new populations have plenty of genetic variety to draw upon.

"From a conservation point of view, [the research] shows that one has to protect species at the regional level, as single populations are genetically diverse because they are colonized by animals that come from genetically diverse populations," Chaturvedi said.

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