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Wikimedia Commons

Painting Frogs, Licking Wounds & Other Adventures with Poisonous Animals

Wikimedia Commons
Wikimedia Commons

In the current issue of the magazine, I’ve got an article called “Fifty Shades of Prey,” about poison dart frogs and some new research into why they come in so many dazzling colors and patterns. 

I was drawn to the story not only because of what Canadian biologist Mathieu Choteau discovered about these frogs (which is pretty cool all by itself), but also by all the stuff he went through along the way. His research involved hand-molding and painting several thousand fake frogs with the help of his girlfriend, getting them on a plane to Peru (worried what airport security might say when they opened his bag), and then painstakingly pinning them to leaves while trudging through the rainforest. 

Going back even further into what we know about dart frogs and other poisonous animals, there are plenty of other intrepid scientists and strange sounding field work. I couldn’t fit all of their stories into the magazine piece, so I wanted to share a little bit about two of them here. 

The first is a guy named John W. Daly. In the early 1960s, not long after he took a job at the National Institutes of Health, he was sent on a research errand by the head of his lab. Certain native tribesmen in Colombia were known to coat the tips of their hunting arrows and blowgun darts with skin secretions from local frogs, which gave the weapons a toxic punch. The senior scientist wanted someone to go down to the rainforest, harvest some frogs, and analyze the chemicals in their skin. He’d been unable to find someone in the lab, though, who 1) had experience in the field and could handle a trip to the rainforest, and 2) he could afford to commit to research that might not pan out. 

Daly fit the bill perfectly. He was a chemist by training, but always had an interest in biology. He’d grown up in Oregon collecting frogs, snakes, and lizards and keeping them in his own little zoo in the basement. He was also young and a new hire, so they could get away with paying less for the field work than the other scientists. 

Daly was soon in the Amazon collecting frogs for a $16 per diem. Without many resources to work with, he developed an unusual way to figure out which frogs were worth examining and which weren’t. He’d slide a finger along a frog's skin, and then touch his tongue. If he experienced a burning sensation in his mouth, then the frog was worth a look. Fortunately, Daly took the locals’ advice about one particular frog. Even experienced tribal hunters only handled Phyllobates terribilis with the utmost care—it’s the most poisonous of the dart frogs and may be the most poisonous vertebrate in the world. 

Daly’s time tasting frogs in the rainforest eventually led to the discovery of the batrachotoxins (“frog poison”), the class of alkaloid poisons that make some of these frogs so deadly. In the early 1970s, Daly and colleagues published the chemical structure of the toxin and detailed its biological effects. 

Almost 20 years later and thousands of miles away, John Dumbacher, a grad student at the University of Chicago, was studying the courtship and mating behaviors of the Raggiana Bird-of-paradise in Papua New Guinea. He and his research team stretched nets between trees to capture the birds for study, and sometimes caught other birds by accident. Some of these were songbirds known as Hooded Pitohuis

As Dumbacher tried to free these birds, they’d bite or scratch at his hands and sometimes he would get cut. Rather than stopping his work and finding a place to wash his wounds, he would usually just pop the injured finger in his mouth to give the cut a quick clean. Just a few minutes later, though, his tongue and lips would start to tingle and burn a little. The sensation wasn’t awful—Dumbacher has compared it to eating a chili pepper or touching your tongue to a 9-volt battery—but it was puzzling, and after another student experienced the same thing, Dumbacher began to wonder if it was the bird’s fault. 

The next time a pitohui got caught in one of the nets, Dumbacher and the other student tasted one of the feathers. Sure enough, their mouths started to tingle and burn. They asked a few of the team’s forest guides about it and learned that the locals called the pitohuis “rubbish birds” or “garbage birds” and wouldn’t eat them, unless they were skinned and specially prepared for safety and flavor. The birds, Dumbacher realized, might be poisonous. 

While poisonous birds were sometimes rumored to exist, none had ever been scientifically confirmed, and the idea wasn’t always considered legitimate. Dumbacher wanted some pitohui feathers analyzed for toxins, but couldn’t find a chemist who would take his hypothesis seriously. Dumbacher returned to the U.S. with a bunch of feathers in 1990. Knowing about Daly’s experience with poisonous vertebrates, he called the NIH, a little bit worried that Daly would laugh him off as “just a nutty kid.” 

Daly was curious, though, and took the feathers and began to run some tests. When he took extracts from the feather and injected them into a mouse, it began to convulse and quickly died. He called Dumbacher back looking for more samples from the birds—the young man seemed to be onto something. 

Daly eventually isolated what he believed to be the toxic compound and had a colleague run a chemical analysis on it. When the colleague called him with the compound’s analysis, Daly recognized the characteristics and patterns immediately. It was the same chemical he’d found, identified, described, and named decades earlier. Batrachotoxin, the “frog poison,” had turned up in a bird.

Daly, Dumbacher, and their colleagues announced their discovery two years later in a paper in Science, and the hooded pitohui became the first confirmed poisonous bird. A decade later, the blue-capped ifrita became the second

What was frog poison doing in two different types of birds? How could the frogs and birds, separated by vast oceans and so many twists and turns of evolutionary history, produce the same toxin—not a similar toxin, but the exact same one?

More than a decade of work by Dumbacher, Daly and other researchers suggests that these odd, toxic bedfellows get their toxins from their diets. In Papua New Guinea, Dumbacher heard reports from locals of a few types of beetle that caused tingling and burning sensations on contact. He found those same beetles in the stomachs of the pitohuis and later found that they contained high concentrations of batrachotoxin. In a 2004 paper, he suggested that the bugs provided a natural toxin source for the birds, and that other bugs might do the same for poison dart frogs. 

Daly had touched on the same idea before, noticing that a change in the frogs’ diet altered their toxic profile. Around the same time as Dumbacher’s study, Daly and colleagues from the NIH and elsewhere found evidence that ants and “moss mites” in Central America contained some of the same alkaloids as the frogs and made up a large portion of their diet. This second study supporting the toxic diet idea was one of the last papers Daly published before his death in 2008. 

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Ted Cranford
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science
Scientists Use a CT Scanner to Give Whales a Hearing Test
Ted Cranford
Ted Cranford

It's hard to study how whales hear. You can't just give the largest animals in the world a standard hearing test. But it's important to know, because noise pollution is a huge problem underwater. Loud sounds generated by human activity like shipping and drilling now permeate the ocean, subjecting animals like whales and dolphins to an unnatural din that interferes with their ability to sense and communicate.

New research presented at the 2018 Experimental Biology meeting in San Diego, California suggests that the answer lies in a CT scanner designed to image rockets. Scientists in San Diego recently used a CT scanner to scan an entire minke whale, allowing them to model how it and other whales hear.

Many whales rely on their hearing more than any other sense. Whales use sonar to detect the environment around them. Sound travels fast underwater and can carry across long distances, and it allows whales to sense both predators and potential prey over the vast territories these animals inhabit. It’s key to communicating with other whales, too.

A CT scan of two halves of a dead whale
Ted Cranford, San Diego State University

Human technology, meanwhile, has made the ocean a noisy place. The propellers and engines of commercial ships create chronic, low-frequency noise that’s within the hearing range of many marine species, including baleen whales like the minke. The oil and gas industry is a major contributor, not only because of offshore drilling, but due to seismic testing for potential drilling sites, which involves blasting air at the ocean floor and measuring the (loud) sound that comes back. Military sonar operations can also have a profound impact; so much so that several years ago, environmental groups filed lawsuits against the U.S. Navy over its sonar testing off the coasts of California and Hawaii. (The environmentalists won, but the new rules may not be much better.)

Using the CT scans and computer modeling, San Diego State University biologist Ted Cranford predicted the ranges of audible sounds for the fin whale and the minke. To do so, he and his team scanned the body of an 11-foot-long minke whale calf (euthanized after being stranded on a Maryland beach in 2012 and preserved) with a CT scanner built to detect flaws in solid-fuel rocket engines. Cranford and his colleague Peter Krysl had previously used the same technique to scan the heads of a Cuvier’s beaked whale and a sperm whale to generate computer simulations of their auditory systems [PDF].

To save time scanning the minke calf, Cranford and the team ended up cutting the whale in half and scanning both parts. Then they digitally reconstructed it for the purposes of the model.

The scans, which assessed tissue density and elasticity, helped them visualize how sound waves vibrate through the skull and soft tissue of a whale’s head. According to models created with that data, minke whales’ hearing is sensitive to a larger range of sound frequencies than previously thought. The whales are sensitive to higher frequencies beyond those of each other’s vocalizations, leading the researchers to believe that they may be trying to hear the higher-frequency sounds of orcas, one of their main predators. (Toothed whales and dolphins communicate at higher frequencies than baleen whales do.)

Knowing the exact frequencies whales can hear is an important part of figuring out just how much human-created noise pollution affects them. By some estimates, according to Cranford, the low-frequency noise underwater created by human activity has doubled every 10 years for the past half-century. "Understanding how various marine vertebrates receive and process low-frequency sound is crucial for assessing the potential impacts" of that noise, he said in a press statement.

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Scientific Reports, Fernando Ramirez Rozzi
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Stones, Bones, and Wrecks
Humans Might Have Practiced Brain Surgery on Cows 5000 Years Ago
Scientific Reports, Fernando Ramirez Rozzi
Scientific Reports, Fernando Ramirez Rozzi

In the 1970s, archaeologists discovered a site in France containing hundreds of cow skeletons dating back 5000 to 5400 years. The sheer number wasn't surprising—human agriculture in that part of the world was booming by 3000 BCE. What perplexed scientists was something uncovered there a few decades later: a cow skull bearing a thoughtfully drilled hole. Now, a team of researchers has released evidence that suggests the hole is an early example of animal brain surgery.

Fernando Ramírez Rozzi, a paleontologist with the French National Center for Scientific Research, and Alain Froment, an anthropologist at the Museum of Mankind in Paris, published their findings in the journal Nature Scientific Reports. After comparing the opening to the holes chiseled into the skulls of humans from the same era, they found the bones bore some striking similarities. They didn't show any signs of fracturing from blunt force trauma; rather, the hole in the cow skull, like those in the human skulls, seemed to have been carved out carefully using a tool made for exactly that purpose. That suggests that the hole is evidence of the earliest known veterinary surgery performed by humans.

Trepanation, or the practice of boring holes into human skulls, is one of the oldest forms of surgery. Experts are still unsure why ancient humans did this, but the level of care that went into the procedures suggests that the surgery was likely used to treat sick patients while they were still alive. Why a person would perform this same surgery on a cow, however, is harder to explain.

The authors present a few theories, the first being that these ancient brain surgeons were treating a sick cow the same way they might treat a sick human. If a cow was suffering from a neural disease like epilepsy, perhaps they though that cutting a hole in its head would relieve whatever was agitating the brain. The cow would have needed to be pretty special to warrant such an effort when there were hundreds of healthy cows living on the same plot of land, as evidenced by the skeletons it was found with.

Another possible explanation was that whoever operated on the cow did so as practice to prepare them for drilling into the heads of live humans one day. "Cranial surgery requires great manual dexterity and a complete knowledge of the anatomy of the brain and vessel distribution," the authors write in the study. "It is possible that the mastery of techniques in cranial surgery shown in the Mesolithic and Neolithic periods was acquired through experimentation on animals."

Either way, the bovine patient didn't live to see the results of the procedure: The bone around the hole hadn't healed at all, which suggests the cow either died during surgery or wasn't alive to begin with.

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