Freshwater Fish

Smarter fish live longer

High levels of predation develop larger brains

Guppies are a popular choice for tropical aquariums around the world. It is a small, colorful and active fish found in most freshwater and brackishwater environments around the world.

Native to parts of the Caribbean and northern South America, populations have been introduced elsewhere, and these are extensive, either accidentally or deliberately for mosquito control.

Scientists studying these fish have found that male guppies that are exposed to high levels of predation often develop larger brains compared to their counterparts living in lower-risk environments.

This would suggest that larger brain size is essential to ensure better survival rates under conditions of high predation. Simply put, these smarter guppies live longer.

Smarter Fish Live Longer

Much of the research on guppies has focused on the female brain, which is physically larger than the male’s. This is because females not only reach a larger adult size, they tend to live longer and have a more careful life history.

Previous research found that female guppies with larger brains preferred to mate with the more vigorous and colorful males. However, at the time, it was unclear whether male guppies had anything to gain from developing larger brains.

The recent research was carried out in northern Trinidad, a country in the southern Caribbean that has had much of its waterways colonized by the ubiquitous native guppy. Two independent rivers were selected and evaluated: the Aripo and the Quare.

Both river routes were marked by waterfalls, and in each case, the area above the waterfall was found to have low numbers of predatory fish, and in the region below the falls, predatory fish were prolific. Male guppies were collected from the areas both above and below the falls on both rivers.

Male guppies located in the predator-poor areas above the waterfalls were found to have, on average, smaller brain sizes compared to their counterparts living below the corresponding waterfall in the more dangerous, predator-rich waters..

However, it was unclear whether guppies had developed larger brains as a result of a long and complex evolutionary process, or whether they were able to increase brain size over a single lifetime as a direct result of exposure to a high-risk environment.

Taking a sample of guppies from waters that contain a large number of predators, the scientists then raised the young of this group in the laboratory.

The pups were divided into two separate groups, and the first was exposed to a predatory fish in an adjacent aquarium (which they could sense through sight and smell) for 5 minutes per session, 5 times per week, for the first 45 days. days of his life. it lives. The second group of guppies was monitored as a control group and housed in a predator-free aquarium.

The results indicated that the males that were exposed to predator cues during their development had much larger brains compared to those in the control group.

Remarkably, under the perceived conditions of threat, the brains of those particular male guppies had become 21% heavier in just 45 days, showing that predation conditions could rapidly influence body attributes among the population. of guppies.

Since male guppies are typically much more colorful compared to females and therefore more obvious to predators, they are naturally smaller than females to help evade predation.

However, it appears that when they are exposed to unusually high numbers of predators, an increase in brain size and mental agility are likely to increase their chances of survival.

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