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John McMillan, Oregon State University

Farmed Fish Can Evolve at a Surprisingly Fast Rate

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John McMillan, Oregon State University

From an evolutionary perspective, every creature on Earth has just one objective: to survive long enough to pass on its genetic material to the next generation. In periods of scarcity or intense competition, only those individuals with a genetic edge will succeed. Such is the case with hatchery-raised fish, which scientists say are evolving with astonishing speed. The researchers published their findings in the journal Nature Communications.

Aquaculture is essential for the global food web. Fish and shellfish are bred and raised in human-controlled environments. Some, like steelhead trout (Oncorhynchus mykiss), are raised in hatcheries, released into the wild, and captured later (that’s the “wild-caught” fish you see on your menu).

"A fish hatchery is a very artificial environment that causes strong natural selection pressures," co-author Michael Blouin said in a press statement. "A concrete box with 50,000 other fish all crowded together and fed pellet food is clearly a lot different than an open stream."

Working in tandem with the Oregon Department of Fish and Wildlife, Blouin and his colleagues sequenced the DNA of both hatchery-raised and wild-origin O. mykiss specimens. As the offspring of wild trout, the hatchery-raised fish represented just a single generation’s experience with captivity.

That single generation was enough to make a huge impact on the hatchery-raised trout's DNA. The researchers found changes in 723 genes. Many of these genetic variations seem to be adaptations to the hatchery environment, where injury and illness are common.

"We observed that a large number of genes were involved in pathways related to wound healing, immunity, and metabolism, and this is consistent with the idea that the earliest stages of domestication may involve adapting to highly crowded conditions," lead author Mark Christie said in the press statement.

“We expected hatcheries to have a genetic impact," Blouin added. "However, the large amount of change we observed at the DNA level was really amazing. This was a surprising result."

The researchers say identifying these changes can highlight issues in hatchery management and may eventually lead to improvements in the way the fish are raised. 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Listen to the Impossibly Adorable Sounds of a Baby Sloth
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RODRIGO ARANGUA/AFP/GettyImages

Sometimes baby sloths seem almost too adorable to be real. But the little muppet-faced treasures don't just look cute—turns out they sound cute, too. We know what you're thinking: How could you have gone your whole life without knowing what these precious creatures sound like? Well, fear not: Just in time for International Sloth Day (today), we have some footage of how the tiny mammals express themselves—and it's a lot of squeaking. (Or maybe that's you squealing?)

The sloths featured in the heart-obliterating video below come from the Sloth Sanctuary of Costa Rica. The institution rescues orphaned sloths, rehabilitates them, and gets them ready to be released back into the wild.

[h/t The Kid Should See This]

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