Guppies Help Scientists Unlock Answer To Major Evolutionary Question

RIVERSIDE, Calif. — Modern science’s understanding of evolution has come a long way since Charles Darwin first published On the Origin of Species in 1859, but there are still many evolutionary secrets researchers are working to unravel. Now, a new study conducted at the University of California, Riverside may have just definitively answered a key evolutionary question — thanks to, of all creatures, guppies!

Do animals evolve in response to the amount of nearby predators? Or do animals evolve in response to the environments they themselves create after finding a safe place to call home? After taking a group of guppies and placing them in a safe, relatively predator-free environment, researchers tracked the fish for four years. According to their findings, the guppies first changed the environment they were living in, and then began evolving in response to their new surroundings.

Guppies were chosen because they have a unique ability to make their way through waterfalls and rapids to safe places where most predators can’t reach them. Furthermore, the tiny fish are also known to evolve quickly and become genetically distinct from their ancestors after reaching a safe environment.

“We already knew that they evolved quickly, but what we didn’t yet understand was why,” comments professor of biology at UC Riverside David Reznick in a media release.

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In order to answer that very question, Reznick and his team traveled all the way to Trinidad, a native habitat for guppies, to conduct an experiment. Researchers took a group of guppies from one area known to contain various predators, and moved the fish to another area largely devoid of predators. Over the course of the next four years, the research team observed the relocated guppies and compared their evolutionary patterns to other guppies living closer to predators.

“If guppies evolve because they aren’t at risk of becoming food for other fish, then evolution should be visible right away,” Reznick explains. “However, if in the absence of predators they become abundant and deplete the environment of food, then there will be a lag in detectable changes.”

Guppies were tagged so they could be easily tracked. Each guppy’s age and size when they reached full maturity was recorded as well, as that is considered a key trait that affects population growth. As the guppy population in the non-predator area increased, changes in the environment were also tracked. The amount of available food, such as algae or insects, was noted, as well as the presence of any other non-predator fish.

After finishing their analysis at the end of the four year observation period, researchers discovered a 2-3 year lag between when the guppies were brought into the new, safer environment, and when evolution started to become apparent. This suggests that the guppies were not evolving simply because they had escaped the predators, but due to the changes in their environment (denser population, less food) that they had brought on themselves.

“The speed of evolution makes it possible to study how it happens,” Reznick says. “The new news is that organisms can shape their own evolution by changing their environment.”

Reznick is currently working on applying these findings to human evolution.

“Unlike guppies and other organisms, human population density seems to increase without apparent limit, which increases our impact on our environment and on ourselves,” he comments.

The study is published in the scientific journal American Naturalist.

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