Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0
Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0

A Fish Parasite May Have Compromised Decades of Behavioral Experiments

Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0
Tohru Murakami via Flickr Creative Commons // CC BY-NC 2.0

Science’s image as an objective collection of facts took another hit this week, as researchers report that a common fish parasite may have skewed the results of thousands of behavioral science studies. They published their findings in the journal Fish Diseases.

Pseudoloma neurophilia is a teeny-tiny type of parasitic fungus called a microsporidium. Microsporidia are prolific and diverse, infecting almost every type of animal on Earth. Symptoms of a microsporidium infection vary by parasite and host species. Sometimes it’s fatal. Other times the effects are so subtle that you’d really have to be looking to notice them.

Fortunately, some scientists are looking. Researchers in the biomedicine and microbiology departments at Oregon State University (OSU) have been tracking P. neurophilia for years—specifically, its effect on Danio rerio, commonly known as the zebrafish.

If you follow science news, you’ve probably heard about zebrafish before. These unassuming little fish have become some of the most popular research animals in the world, thanks to their low-maintenance lifestyle, susceptibility to drugs and genetic changes, and enormous broods. They’re also incredibly social, which has led researchers to consider them a good model for people. Consequently, we use them to test pharmaceuticals, hunt for clues to genetic disease, and even explore the roots of human behavior.

Studies of D. rerio’s social activity often center around one specific behavior: huddling. Stressed zebrafish band together in groups called shoals, while healthy, calm fish tend to spread themselves wider apart. So researchers generally assume that clustering fish have been negatively affected in some way by experimental treatment, whether that’s a drug or a gene associated with disease.

But there’s more to it, say the OSU scientists. Their studies of P. neurophilia suggested to them that the parasite could be quietly changing zebrafish behavior. To find out, they brought 140 zebrafish into the lab and divided them into 12 tanks of 10 fish and one “sentinel tank” of 20. They set up cameras by the 12 test tanks and took still images at regular intervals.

Then, the team added water to all the tanks. Six exposure tanks, and the sentinel tank, were topped up with water from a tank of infected fish. The remaining six tanks got water from a parasite-free tank.

Once again, the researchers trained their cameras on the swimming fish, monitoring their movement. Analysis of the tank snapshots showed that fish exposed to the parasite were more likely to stick together than fish in the clean tanks. The researchers noted that fish in the parasite-treated tanks stuck even more closely together than fish in other studies who had been dosed with stress-inducing chemicals.

Postmortem examinations of fish from each group confirmed that the presence of P. neurophilia in the water was more than enough to infect a tank’s inhabitants. None of the fish from the control tanks were infected, but nearly all the fish from the parasite-treated tanks were.

The team’s earlier work has shown that infection with the microsporidium is very, very common in laboratory zebrafish populations. Lead author and veterinary surgeon Sean Spagnoli noted that some researchers might not even check to see if their fish are sick.

“I haven't seen a single paper that stated that ‘fish used were certified pathogen-free for P. neurophilia'," he told Nature.

This wouldn't be the first time scientists have overlooked a big variable. A study published earlier this year found that lab mice get chilled, stressed, and sick at normal laboratory temperatures. Another concluded that software design issues may have led to false positives in thousands of brain scan studies.

University College London geneticist Elena Dreosti isn't sure that's what's happening here. Speaking to Nature, she argued that the study’s results are statistically weak.

“Considerable additional work is needed to know if this is likely to have a significant impact on the type of behaviour research that is done by the community working with zebrafish,” she said in Nature. Other researchers have expressed doubts about the precision of measuring intra-fish distances through snapshots.

The OSU team stands by their methods and findings, but will continue to study the issue.

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Slow Motion Is the Only Way to Appreciate a Chameleon’s Lightning-Fast Tongue

From the unusual way they walk, to their ability to change color, the evolutionary adaptations of chameleons are pretty bizarre, and some of them remain mysterious even to scientists. Their super-powered tongues, for instance, can dart out so quickly that the movement can barely be seen with the naked eye. But modern high-speed cameras have enabled researchers at the University of South Dakota to observe this appendage at work like never before. The video below, shared over at The Kid Should See This, includes some of that groundbreaking footage, and it's pretty amazing to watch.

Shooting at 3000 frames per second, the camera was able to capture every split-second aspect of the chameleon's tongue strike. Slowed down, the video allows you to see how every component of the process works in harmony: First, muscles in the lizard’s tongue contract like the string of a bow. Then, when that tension is released, the bony base of the tongue shoots forward, pushing the sticky, elastic part toward the chameleon’s prey.

According to Christopher Anderson, one of the scientists who conducted the high-speed camera research, larger chameleons can catapult their tongues forward at distances of one to two times their body length. For smaller chameleons, this distance can reach up to two and a half times their body length. “Small chameleons need to be able to eat more food for their body size than large chameleons,” he tells bioGraphic in the video, “and so by being able to project their tongues proportionately further than these large species, they basically are opening up additional feeding opportunities to themselves that they wouldn’t have if they had a shorter tongue.”

To see one of nature’s greatest hunting tools in action, check out the full video below.

[h/t The Kid Should See This]

There May Be an Ancient Reason Why Your Dog Eats Poop

Dogs aren't known for their picky taste in food, but some pups go beyond the normal trash hunting and start rooting around in poop, whether it be their own or a friend's. Just why dogs exhibit this behavior is a scientific mystery. Only some dogs do it, and researchers aren't quite sure where the impulse comes from. But if your dog is a poop eater, it's nearly impossible to steer them away from their favorite feces.

A new study in the journal Veterinary Medicine and Science, spotted by The Washington Post, presents a new theory for what scientists call "canine conspecific coprophagy," or dogs eating dog poop.

In online surveys about domestic dogs' poop-eating habits completed by thousands of pet owners, the researchers found no link between eating poop and a dog's sex, house training, compulsive behavior, or the style of mothering they received as puppies. However, they did find one common link between the poop eaters. Most tended to eat only poop that was less than two days old. According to their data, 85 percent of poop-eaters only go for the fresh stuff.

That timeline is important because it tracks with the lifespan of parasites. And this led the researchers to the following hypothesis: that eating poop is a holdover behavior from domestic dogs' ancestors, who may have had a decent reason to tuck into their friends' poop.

Since their poop has a high chance of containing intestinal parasites, wolves poop far from their dens. But if a sick wolf doesn't quite make it out of the den in time, they might do their business too close to home. A healthier wolf might eat this poop, but the parasite eggs wouldn't have hatched within the first day or two of the feces being dropped. Thus, the healthy wolf would carry the risk of infection away from the den, depositing the eggs they had consumed away in their own, subsequent bowel movements at an appropriate distance before the eggs had the chance to hatch into larvae and transmit the parasite to the pack.

Domestic dogs may just be enacting this behavior instinctively—only for them, there isn't as much danger of them picking up a parasite at home. However, the theory isn't foolproof. The surveys also found that so-called "greedy eaters" were more likely to eat feces than dogs who aren't quite so intense about food. So yes, it could still be about a poop-loving palate.

But really, it's much more pleasant to think about the behavior as a parasite-protection measure than our best pals foraging for a delicious fecal snack. 

[h/t The Washington Post]


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