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The Invasive Species That Couldn’t Invade

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The red shiner is just a few inches long, and has no big scary fangs, no claws, no stinger, and no poisonous spines. The little minnow probably isn’t an animal that would ever strike fear in anyone’s heart, but it’s a fierce conqueror. 

In fact, on paper, they seem like the perfect invasive species. They can live and reproduce almost anywhere, tolerate extreme conditions like high-temperature and low-oxygen water, eat almost anything, grow rapidly, and produce large numbers of young. And sure enough, after accidental releases from bait farms, they’re now found in a dozen states outside their native range. In their conquered territory, shiners are considered a serious threat to native species because they displace and outcompete them, prey on their young, introduce tapeworms and other parasites, and dilute gene pools through hybridization. 

All this suggests that red shiners should be able to go wherever they please. But for some reason, they can’t go back home. 

The shiner is native to a broad swath of the Mississippi River basin and, for almost half a century, was abundant in the creeks that fed into Lake Texoma in southern Oklahoma. Over the last few decades, though, they’ve all but disappeared there. Populations that used to number in the hundreds in the 1980s dropped to just single digits in the late '90s and early 2000s. 

This doesn’t seem to be for lack of effort on the minnows' part, though, and surveys from recent years showed a mysterious pattern of reappearance and disappearance. After severe flooding in the area in the summer of 2007, previously impassable stretches of dry land were re-watered and the minnows re-colonized their old stomping grounds. In June 2009, researchers found 81 shiners in one of the creeks. Two months later, there were only four. By November, there was just one. Then that was gone, too. Just as quickly as they settled in, the fish disappeared again. 

The minnows were still abundant in other nearby streams, though, so the problem didn’t appear to be a total loss of the species in the area. It was just this handful of creeks that they couldn’t get a foothold in. 

They say you can never go home again, and it looked like the shiners would agree. The little minnow that couldn’t presented scientists with a natural paradox, one that turned the standard invasive species narrative on its head. Why, biologists wondered, despite their abundance, tolerance of harsh conditions and invasiveness, couldn’t the fish re-invade the creeks they’d come from?

To find out what had locked the shiners out, University of Oklahoma zoologists Edie Marsh-Matthews, William Matthews, and Nathan Franssen decided to watch a shiner homecoming unfold. They built an artificial stream that mimicked the conditions and native fish populations of Brier Creek, where the shiners were losing the most ground after re-invasion. 

After the other fish—which included stonerollers, bigeye shiners, blackstripe topminnows and green sunfish—had time to establish themselves, the shiners were thrown into the mix in a mock invasion. At first, they seemed right at home. They were healthy, they ate well and the males chased and circled the females in the shiner equivalent of courting. By the end of the experiments, though, only 20 percent of the invaders survived. Even in a fake stream, they’d failed again. 

The three scientists searched for reasons for the die-off, but couldn’t find anything. They’d stocked enough shiners at the start of the experiment. The water chemistry looked fine. The filters were clean. The algae cover was ideal. Shiners had successfully reproduced and raised young and thrived in similar experiments when housed alone, so maybe the problem was one of the other fish. 

The researchers found that the more adult sunfish there were in the stream during the experiments, the fewer shiners they wound up with in the end. The sunfish didn’t seem like likely suspects at first glance. They’d been stocked at the start of the experiment as small juveniles, hardly anything to worry about, and no one directly saw them preying on the shiners. But sunfish grow quickly, and by the end of the study, they were significantly larger and could pose a serious threat to the invaders.

Death-by-sunfish fit the timeline for what was happening in the wild, too. A group of invading red shiners, swimming into the creeks during spring and summer floods, would encounter juvenile sunfish that primarily eat insects. Given a summer to grow, the larger sunfish would start mixing small fish into their diet right around the time when the survey noted the shiners disappearing. 

The shiners’ failure to reinvade looks like just a matter of being in the wrong place at the wrong time. They’d come home again just before they would get added to their neighbors’ menu. Their behavior doesn’t help, either. In the experiments, the shiners tended to swim at midwater where sunfish hunt, and engaged in less defensive behavior in the face of danger. The small native fish like the bigeye shiners, on the other hand, mostly swam closer to the surface and stayed in parts of the stream that were too shallow for the larger predators. 

As destructive as invasive species can be, the shiners show that even an invader can sometimes be an underdog.

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Big Questions
Why Do Cats 'Blep'?
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As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
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If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

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
Why Crows Hold Noisy Funerals for Their Fallen Friends
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The next time you hear a murder of crows cackling for no apparent reason, show a little respect: You may have stumbled onto a crow funeral. Crows are among the few animals that exhibit a social response to a dead member of their species. Though their caws may sound like heartbroken cries, such funerals aren't so much about mourning their fallen friends as they are about learning from their mistakes.

In the video below from the PBS series Deep Look, Kaeli Swift, a researcher at the University of Washington's Avian Conservation Lab, investigates this unusual phenomenon firsthand. She familiarized herself with a group of crows in a Seattle park by feeding them peanuts in the same spot for a few days. After the crows got used to her visits, she returned to the site holding a dead, taxidermied crow and wearing a mask and wig to hide her identity. The crows immediately started their ritual by gathering in the trees and crying in her direction. According to Swift, this behavior is a way for crows to observe whatever might have killed the dead bird and learn to avoid the same fate. Flocking into a large, noisy group provides them protection from the threat if it's still around.

She tested her theory by returning to the same spot the next week without her mask or the stuffed crow. She offered the crows peanuts just as she had done before, only this time the birds were skittish and hesitant to take them from her. The idea that crows remember and learn from their funerals was further supported when she returned wearing the mask and wig. Though she didn't have the dead bird with her this time, the crows were still able to recognize her and squawked at her presence. Even birds that weren't at the funeral learned from the other birds' reactions and joined in the ruckus.

Swift was lucky this group of crows wasn't particularly vengeful. Crows have been known to nurse and spread grudges, sometimes dive-bombing people that have harmed one of their own.

[h/t Deep Look]

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