Isegoria

Like other rodents, hamsters are highly motivated to run in wheels:

It is not uncommon to record distances of 9 km (5.6 mi) being run in one night. Other 24-h records include 43 km (27 mi) for rats, 31 km (19 mi) for wild mice, 19 km (12 mi) for lemmings, 16 km (9.9 mi) for laboratory mice, and 8 km (5.0 mi) for gerbils.

Hypotheses to explain such high levels of running in wheels include a need for activity, substitute for exploration, and stereotypic behaviour. However, free wild mice will run on wheels installed in the field, which speaks against the notion of stereotypic behaviour induced by captivity conditions. Alternatively, various experimental results strongly indicate that wheel-running, like play or the endorphin or endocannabinoid release associated with the ‘runner’s high’, is self-rewarding. Wheel use is highly valued by several species as shown in consumer demand studies which require an animal to work for a resource, i.e. bar-press or lift weighted doors. This makes running wheels a popular type of enrichment to the captivity conditions of rodents.

Captive animals continue to use wheels even when provided with other types of enrichment. In one experiment, Syrian hamsters that could use tunnels to access five different cages, each containing a toy, showed no more than a 25% reduction in running-wheel use compared to hamsters housed in a single cage without toys (except for the running wheel).

In another study, female Syrian hamsters housed with a nest-box, bedding, hay, paper towels, cardboard tubes, and branches used a wheel regularly, and benefited from it as indicated by showing less stereotypic bar-gnawing and producing larger litters of young compared to females kept under the same conditions but without a wheel. Laboratory mice were prepared to perform more switch presses to enter a cage containing a running wheel compared to several meters of Habitrail tubing or a torus of Habitrail tubing.

Running in wheels can be so intense in hamsters that it may result in foot lesions, which appear as small cuts on the paw pads or toes. Such paw wounds rapidly scab over and do not prevent hamsters from continuing to run in their wheel.

A hamster in a running wheel equipped with a generator can generate up to 500 mW electric power, enough for illuminating small LED lamps.

(Hat tip to our Slovenian Guest.)

Eugène Dubois gathered the brain and body weights of several dozen animal species and calculated the mathematical rate at which brain size expands relative to body size:

Dubois reasoned that as body size increases, the brain must expand for reasons of neural housekeeping: Bigger animals should require more neurons just to keep up with the mounting chores of running a larger body. This increase in brain size would add nothing to intelligence, he believed. After all, a cow has a brain at least 200 times larger than a rat, but it doesn’t seem any smarter. But deviations from that mathematical line, Dubois thought, would reflect an animal’s intelligence. Species with bigger-than-predicted brains would be smarter than average, while those with smaller-than-predicted brains would be dumber. Dubois’s calculations suggested that his Java Man was indeed a smart cookie, with a relative brain size — and intelligence — that fell somewhere between modern humans and chimpanzees.

Dubois’s formula was later revised by other scientists, but his general approach, which came to be known as “allometric scaling,” persisted. More modern estimates have suggested that the mammalian brain mass increases by an exponent of two-thirds compared to body mass. So a dachshund, weighing roughly 27 times more than a squirrel, should have a brain about 9 times bigger — and in fact, it does. This concept of allometric scaling came to permeate the discussion of how brains relate to intelligence for the next hundred years.

Seeing this uniform relationship between body and brain mass, scientists developed a new measure called encephalization quotient (EQ). EQ is the ratio of a species’s actual brain mass to its predicted brain mass. It became a widely used shorthand for intelligence. As expected, humans led the pack with an EQ of 7.4 to 7.8, followed by other high achievers such as dolphins (about 5), chimpanzees (2.2 to 2.5), and squirrel monkeys (roughly 2.3). Dogs and cats fell in the middle of the pack, with EQs of around 1.0 to 1.2, while rats, rabbits, and oxen brought up the rear, with values of 0.4 to 0.5. This way of thinking about brains and intelligence has been “very, very dominant” for decades, says Evan MacLean, an evolutionary anthropologist at the University of Arizona in Tucson. “It’s sort of a fundamental insight.”

A century later, Suzana Herculano-Houzel found a (gruesome) way to count neurons efficiently:

An entire rat brain contains about 200 million nerve cells.

She looked at brains from five other rodents, from the 40-gram mouse to the 48-kilogram capybara (the largest rodent in the world, native to Herculano-Houzel’s home country of Brazil). Her results revealed that as brains get larger and heavier from one species of rodent to another, the number of neurons grows more slowly than the mass of the brain itself: A capybara’s brain is 190 times larger than a mouse’s, but it has only 22 times as many neurons.

Then in 2006, Herculano-Houzel got her hands on the brains of six primate species during a visit with Jon Kaas, a brain scientist at Vanderbilt University in Nashville, Tennessee. And this is where things got even more interesting.

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As the primate brain expands from one species to another, the number of neurons rises quickly enough to keep pace with the growing brain size. This means that the neurons aren’t ballooning in size and taking up more space, as they do in rodents. Instead, they stay compact. An owl monkey, with a brain twice as large as a marmoset, actually has twice as many neurons — whereas doubling the size of a rodent brain often yields only 20 to 30 percent more neurons. And a macaque monkey, with a brain 11 times larger than a marmoset, has 10 times as many nerve cells.

[...]

The usual curse of an ever-expanding neuron size may stem from the basic fact that brains function as networks in which individual neurons send signals to one another. As brains get bigger, each nerve cell must stay connected with more and more other neurons. And in bigger brains, those other neurons are located farther and farther away.

[...]

A large rodent called an agouti has eight times as many cortical nerve cells as a mouse, while its white matter takes up an astonishing 77 times as much space. But a capuchin monkey, with eight times as many cortical neurons as a small primate called a galago, has only 11 times as much white matter.

[...]

Kaas thinks that primates managed to keep most of their neurons the same size by shifting the burden of long-distance communication onto a small subset of nerve cells. He points to microscopic studies showing that perhaps 1 percent of neurons do expand in big-brained primates: These are the neurons that gather information from huge numbers of nearby cells and send it to other neurons that are far away. Some of the axons that make these long-distance connections also get thicker; this allows time-sensitive information, such as a visual image of a rapidly moving predator, or prey, to reach its destination without delay. But less-urgent information — that is, most of it — is sent through slower, skinnier axons. So in primates, the average thickness of axons doesn’t increase, and less white matter is needed.

This pattern of keeping most connections local, and having only a few cells transmit information long-distance, had huge consequences for primate evolution. It didn’t merely allow primate brains to squeeze in more neurons. Kaas thinks that it also had a more profound effect: It actually changed how the brain does its work. Since most cells communicated only with nearby partners, these groups of neurons became cloistered into local neighborhoods. Neurons in each neighborhood worked on a specific task — and only the end result of that work was transmitted to other areas far away. In other words, the primate brain became more compartmentalized. And as these local areas increased in number, this organizational change allowed primates to evolve more and more cognitive abilities.

All mammal brains are divided into compartments, called “cortical areas,” that each contain a few million neurons. And each cortical area handles a specialized task: The visual system, for example, includes different areas for spotting the simple edges of shapes and for recognizing objects. Rodent brains don’t seem to become more compartmentalized as they get larger, says Kaas. Every rodent from the bite-sized mouse to the Doberman-sized capybara has about the same number of cortical areas — roughly 40. But primate brains are different. Small primates, such as galagos, have around 100 areas; marmosets have about 170, macaques about 270 — and humans around 360.

Imagine emerging into the sun after 17 long years spent lying underground, Ed Yong suggests, only for your butt to fall off:

That ignominious fate regularly befalls America’s cicadas. These bugs spend their youth underground, feeding on roots. After 13 or 17 years of this, they synchronously erupt from the soil in plagues of biblical proportions for a few weeks of song and sex. But on their way out, some of them encounter the spores of a fungus called Massospora.

A week after these encounters, the hard panels of the cicadas’ abdomens slough off, revealing a strange white “plug.” That’s the fungus, which has grown throughout the insect, consumed its organs, and converted the rear third of its body into a mass of spores. The de-derriered insects go about their business as if nothing unusual has happened. And as they fly around, the spores rain down from their exposed backsides, landing on other cicadas and saturating the soil. “We call them flying saltshakers of death,” says Matt Kasson, who studies fungi at West Virginia University.

Massospora and its butt-eating powers were first discovered in the 19th century, but Kasson and his colleagues have only just shown that it has another secret: It doses its victims with mind-altering drugs. Perhaps that’s why “the cicadas walk around as if nothing’s wrong even though a third of their body has fallen off,” Kasson says.

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Greg Boyce, a member of Kasson’s team, looked at all the chemicals found in the white fungal plugs of the various cicadas. And to his shock, he found that the banger-wings were loaded with psilocybin—the potent hallucinogen found in magic mushrooms. “At first, I thought: There’s absolutely no way,” he says. “It seemed impossible.” After all, no one has ever detected psilocybin in anything other than mushrooms, and those fungi have been evolving separately from Massospora for around 900 million years.

The surprises didn’t stop there. “I remember looking over at Greg one night and he had a strange look on his face,” Kasson recalls. “He said, ‘Have you ever heard of cathinone?’” Kasson hadn’t, but a quick search revealed that it’s an amphetamine. It had never been found in a fungus before. Indeed, it was known only from the khat plant that has long been chewed by people from the Middle East and the Horn of Africa. But apparently, cathinone is also produced by Massaspora as it infects periodical cicadas.

[...]

Infected cicadas behave strangely. Despite their horrific injuries, males become hyperactive and hypersexual. They frenetically try to mate with anything they can find, including with other males. They’ll even mimic the wing-flicking signals of females to lure males toward them. None of this does them any good—their genitals have either been devoured by the fungus or have fallen off with the rest of their butts. Instead, this behavior only benefits the fungus, allowing its spores to find new hosts.

Kasson suspects that cathinone and psilocybin are responsible for at least some of these behaviors. “If I had a limb amputated, I probably wouldn’t have a lot of pep in my step,” he said. “But these cicadas do. Something is giving them a bit more energy. The amphetamine could explain that.”

Psilocybin’s role is harder to explain. The drug might make humans hallucinate, but no one knows if cicadas would similarly trip. There is, however, a theory that magic mushrooms evolved psilocybin to reduce the appetites of insects that might compete with them for decaying wood. Perhaps by suppressing the appetites of cicadas, Massospora nudges them away from foraging and toward incessant mating.

There are many parasitic fungi that manipulate the behavior of insect hosts, including the famous Ophiocordyceps fungi, which can turn ants into zombies.

This is how a zombie outbreak could (semi-plausibly) happen.

The saiga is “an endearing antelope” that roams Central Asia. Its “bulbous nose gives it the comedic air of a Dr. Seuss character,” Ed Yong says:

It typically wanders over large tracts of Central Asian grassland, but every spring, tens of thousands of them gather in the same place to give birth. These calving aggregations should be joyous events, but the gathering in May 2015 became something far more sinister when 200,000 saiga just dropped dead. They did so without warning, over a matter of days, in gathering sites spread across 65,000 square miles — an area the size of Florida. Whatever killed them was thorough and merciless: Across a vast area, every last saiga perished.

At first, the team suspected that a new infectious disease had spread through the population, but the pattern of deaths just didn’t fit. The saiga were dying too synchronously and too quickly. Also, all of them had died. “In biology, there’s certain rules, you know?” says Kock. “We accept that sometimes microbes can cause us harm, but not like this. Even very severe viral diseases or anthrax don’t do this. A good proportion of the animals would be fine.”

News of the die-off sparked outlandish explanations about Russian rocket fuel, radiation, and even aliens. But while conspiracy theories raged, a huge international team of scientists, led by Kock, got to work. Vets autopsied as many saigas as they could. Ecologists sampled the soil. Botanists checked the local plants. They couldn’t find any signs of toxins that might have killed the saiga. Instead, the actual culprit turned out to be a bacterium, one that’s usually harmless.

Pasteurella multocida normally lives in the saiga’s respiratory tract, but Kock’s team found that the microbe had found its way into the animals’ blood, and invaded their livers, kidneys, and spleens. Wherever it went, it produced toxins that destroyed the local cells, causing massive internal bleeding. Blood pooled around their organs, beneath their skin, and around their lungs. The saigas drowned in their own bodily fluids.

But that answer just led to more questions. Pasteurella is common and typically harmless part of the saiga’s microbiome. In livestock, it can cause disease when animals are stressed, as sometimes happens when they’re shipped over long distances in bad conditions. But it has never been linked to a mass die-off of the type that afflicted the saigas. What could have possibly turned this docile Jekyll into such a murderous Hyde?

The team considered a list of possible explanations that runs to 13 pages. They wondered if some environmental chemical or dietary change had set the microbe off. They checked if biting insects had transmitted a new infection that interacted with Pasteurella. They considered that Pasteurella might have gone rogue because of an accompanying viral infection, in the same way that Streptococcus bacteria can bloom during a cold, leading to strep throat. “We tested for everything and we couldn’t find anything,” says Eleanor Milner-Gulland from the University of Oxford.

Only one factor fit the bill: climate. The places where the saigas died in May 2015 were extremely warm and humid. In fact, humidity levels were the highest ever seen the region since records began in 1948. The same pattern held for two earlier, and much smaller, die-offs from 1981 and 1988. When the temperature gets really hot, and the air gets really wet, saiga die. Climate is the trigger, Pasteurella is the bullet.

It’s still unclear how heat and humidity turn Pasteurella into a killer, and the team is planning to sequence the bacterium’s genome to find out more.

Blackbirds, Ed Yong explains, aren’t actually all that black:

Their feathers absorb most of the visible light that hits them, but still reflect between 3 and 5 percent of it. For really black plumage, you need to travel to Papua New Guinea and track down the birds of paradise.

Although these birds are best known for their gaudy, kaleidoscopic colors, some species also have profoundly black feathers. The feathers ruthlessly swallow light and, with it, all hints of edge or contour. They make body parts seem less like parts of an actual animal and more like gaping voids in reality. They’re blacker than black. None more black.

By analyzing museum specimens, Dakota McCoy, from Harvard University, has discovered exactly how the birds achieving such deep blacks. It’s all in their feathers’ microscopic structure.

A typical bird feather has a central shaft called a rachis. Thin branches, or barbs, sprout from the rachis, and even thinner branches—barbules—sprout from the barbs. The whole arrangement is flat, with the rachis, barbs, and barbules all lying on the same plane. The super-black feathers of birds of paradise, meanwhile, look very different. Their barbules, instead of lying flat, curve upward. And instead of being smooth cylinders, they are studded in minuscule spikes. “It’s hard to describe,” says McCoy. “It’s like a little bottle brush or a piece of coral.”

These unique structures excel at capturing light. When light hits a normal feather, it finds a series of horizontal surfaces, and can easily bounce off. But when light hits a super-black feather, it finds a tangled mess of mostly vertical surfaces. Instead of being reflected away, it bounces repeatedly between the barbules and their spikes. With each bounce, a little more of it gets absorbed. Light loses itself within the feathers.

McCoy and her colleagues, including Teresa Feo from the National Museum of Natural History, showed that this light-trapping nanotechnology can absorb up to 99.95 percent of incoming light. That’s between 10 and 100 times better than the feathers of most other black birds, like crows or blackbirds. It’s also only just short of the blackest materials that humans have designed. Vantablack, an eerily black substance produced by the British company Surrey Nanosystems, can absorb 99.965 percent of incoming light. It consists of a forest of vertical carbon nanotubes that are “grown” at more than 750 degrees Fahrenheit. The birds of paradise mass-produce similar forests, using only biological materials, at body temperature.

Swamp Park, in southeastern North Carolina, is at the northern extreme for American alligators, which means it can get a little cold for the cold-blooded reptiles:

At first, [George Howard, the park’s general manager] thought the water had too many cypress knees – woody projections from tree roots that are a common sight in swamps.

Then he saw teeth.

When it’s cold but not icy, the alligators disappear, sinking to the bottom of the swamp for most of the day or burrowing into the mud, Howard said. “You don’t see them, but they’re under there.”

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Right before the surface freezes, they stick their snouts out of the water so they can continue breathing.

Iguanas, by the way, react somewhat differently to the cold:

And in Florida, where temperatures took a rare dip into the 40s last week, iguanas also slowed their bodily functions. But because many are tree dwellers, some just fell to the ground.

It was a repeat of a cold snap in 2010, when the iguana situation caught people similarly unawares.

“Neighbourhoods resounded with the thud of iguanas dropping from trees onto patios and pool decks, reptilian Popsicles that suggested the species may not be able to retain its claw-hold on South Florida,” the Sun-Sentinel’s David Fleshler wrote.

But the story had a happy ending, Fleshler reported. The iguanas “have rebounded, repopulating South Florida neighbourhoods and resuming their consumption of expensive landscaping.”

By the way, the term brumation was coined in 1965, so reptiles could have their own term for hibernation.