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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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Animals
Pigeons Are Secretly Brilliant Birds That Understand Space and Time, Study Finds
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Of all the birds in the world, the pigeon draws the most ire. Despite their reputation as brainless “rats with wings,” though, they’re actually pretty brilliant (and beautiful) animals. A new study adds more evidence that the family of birds known as pigeons are some of the smartest birds around, as Quartz alerts us.

In addition to being able to distinguish English vocabulary from nonsense words, spot cancer, and tell a Monet from a Picasso, pigeons can understand abstract concepts like space and time, according to the new study published in Current Biology. Their brains just do it in a slightly different way than humans’ do.

Researchers at the University of Iowa set up an experiment where they showed pigeons a computer screen featuring a static horizontal line. The birds were supposed to evaluate the length of the line (either 6 centimeters or 24 centimeters) or the amount of time they saw it (either 2 or 8 seconds). The birds perceived "the longer lines to have longer duration, and lines longer in duration to also be longer in length," according to a press release. This suggests that the concepts are processed in the same region of the brain—as they are in the brains of humans and other primates.

But that abstract thinking doesn’t occur in the same way in bird brains as it does in ours. In humans, perceiving space and time is linked to a region of the brain called the parietal cortex, which the pigeon brains lack entirely. So their brains have to have some other way of processing the concepts.

The study didn’t determine how, exactly, pigeons achieve this cognitive feat, but it’s clear that some other aspect of the central nervous system must be controlling it. That also opens up the possibility that other non-mammal animals can perceive space and time, too, expanding how we think of other animals’ cognitive capabilities.

[h/t Quartz]

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The Queen's Racing Pigeons Are in Danger, Due to an Increase in Peregrine Falcons
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Queen Elizabeth is famous for her love of corgis and horses, but her pet pigeons don't get as much press. The monarch owns nearly 200 racing pigeons, which she houses in a luxury loft at her country estate, Sandringham House, in Norfolk, England. But thanks to a recent boom in the region’s peregrine falcon population, the Queen’s swift birds may no longer be able to safely soar around the countryside, according to The Telegraph.

Once endangered, recent conservation efforts have boosted the peregrine falcon’s numbers. In certain parts of England, like Norfolk and the city of Salisbury in Wiltshire, the creatures can even find shelter inside boxes installed at local churches and cathedrals, which are designed to protect potential eggs.

There’s just one problem: Peregrine falcons are birds of prey, and local pigeon racers claim these nesting nooks are located along racing routes. Due to this unfortunate coincidence, some pigeons are failing to return to their owners.

Pigeon racing enthusiasts are upset, but Richard Salt of Salisbury Cathedral says it's simply a case of nature taking its course. "It's all just part of the natural process,” Salt told The Telegraph. "The peregrines came here on their own account—we didn't put a sign out saying 'room for peregrines to let.' Obviously we feel quite sorry for the pigeons, but the peregrines would be there anyway."

In the meantime, the Queen might want to keep a close eye on her birds (or hire someone who will), or consider taking advantage of Sandringham House's vast open spaces for a little indoor fly-time.

[h/t The Telegraph]

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