peregrine falcon

<p>See the world through the eyes of nature’s fastest animal: the peregrine falcon. Though once perilously endangered in the U.S., this spectacular predator is now thriving again in American cities and on every continent but Antarctica. What is the secret to its predatory prowess? To find out, follow a young family of peregrines in urban Chicago as the chicks hatch and learn from their parents to fly and hunt. And join expert falconer Lloyd Buck as he trains a captive peregrine and puts its hunting skills to the test. What’s the secret behind the peregrine falcon’s blistering speed, able to reach nearly 200 mph? (Premiered November 21, 2018)</p>

<p>See the world through the eyes of nature’s fastest animal—the peregrine falcon.</p>

World's Fastest Animal

Camila_ferrara_tartaruga P expansa hatchling.jpg

<p>Forty years of community engagement has brought the freshwater turtles of Brazil back from the brink—but lack of funding may imperil conservation.</p>

Amazon Turtles Recovering, Thanks to Local Volunteers

Whit Welles Wikimedia Commons Humpback Whale, breaching, Stellwagen Bank National Marine Sanctuary.jpg

<p>Drowned out by the din of passing ships, humpback whales attempting to breed off the coast of Japan are cutting their conversations short.</p>

Ship Noises Mute the Songs of Humpback Whales

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Nature

Koch Foundation

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      <div class="rich-text"><p>It might sound nuts. But the squirrels are <i>definitely</i> listening.</p><p>For years, researchers have known that squirrels can eavesdrop on other species’ alarm calls to cue into dangerous situations that they might not notice themselves. Now, a team of scientists has uncovered another facet of these rodents’ nosy nature: To figure out when a threat has passed, squirrels may also snoop on the casual conversation of birds—a clear sign that things are, once again, all good in the wooded neighborhood.</p></div>
  

  
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      <div class="rich-text"><p>The <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0221279">study</a>, published today in the journal <i>PLOS ONE,</i> hints that, even for wildlife, the language of safety operates on something of a sliding scale. Rather than relying on the mere <i>absence</i> of an alarm, squirrels will prick their ears for the <i>presence</i> of another signal to confirm the coast is clear—even if that means dissecting the dialect of another species.</p><p>This rudimentary multilingualism is a testament to squirrels’ cognition, which is “much more complex than people give them credit for,” says <a href="https://suzannemacdonald.ca/">Suzanne MacDonald</a>, who studies animal behavior at York University in Canada, but was not involved in the study. “Safety is sometimes seen as the default: When you don’t hear this sound, it’s safe. But this takes it a step further...and that makes it much more interesting.”</p>
            <figure class="richtext-image full-width"><img alt="iStock-1131581504.jpg" class="richtext-image full-width" height="565" width="800"
            src="/wgbh/nova/media/images/iStock-1131581504.width-800.jpg"/><figcaption><p>The world is a scary, scary place. Image Credit: Dgwildlife, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>Most humans may not care for it (<a href="https://www.ammoland.com/2019/01/is-the-tradition-squirrel-hunting-dying-out/">anymore</a>), but squirrel meat has lost none of its allure with the rest of the animal kingdom. Whether they’re traversing the trees or skittering across manicured lawns, these rodents have plenty of predators to fear—which means they need all the help they can get to avoid becoming lunch.</p><p>So perhaps it’s no surprise that they’ve learned the lingo of certain birds, which will squawk, caw, chirp, or even shriek out a warning after they sense a predator on the prowl. Though these alarm calls are probably intended for the birds’ feathered kin, keen-eared squirrels have been caught <a href="https://onlinelibrary.wiley.com/doi/pdf/10.1111/eth.12145">tuning in as well</a>.</p></div>
  

  
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      <div class="rich-text"><p>But a few years ago, Oberlin College behavioral ecologist <a href="https://www.oberlin.edu/keith-tarvin">Keith Tarvin</a> started to wonder if alarm calls were only half of the squirrel eavesdropping equation. “There’s a lot of information in alarm calls,” he says. “It dawned on us that cues of safety might be equally informative.”</p><p>When a squirrel has reason to believe a crisis is afoot, it’ll drop whatever it’s doing and reallocate all its energy into a set of vigilance behaviors, like rearing up on its hind legs to scan its surroundings, freezing in place, or fleeing the danger zone entirely. But staying in this stressful state is exhausting, and saps time and energy from other essential tasks like foraging for food or wooing a potential mate. That means having an obvious off switch for predator surveillance could be as important as the trigger that turns it on.</p><p>To explore this side of the story, Tarvin and his students, <a href="https://www.linkedin.com/in/marie-lilly-a237a612b/">Marie Lilly</a> and Emma Lucore, both Oberlin undergraduates at the time, decided to scare the crap out of a scurry of eastern gray squirrels (<i>Sciurus carolinensis</i>)—and then try to calm them back down. On mild winter days, Lilly would hoist a set of speakers onto her bicycle and search out squirrels near the university’s campus. Once she found a potential candidate, she’d play it a brief recording of the cries of a red-tailed hawk (<i>Buteo jamaicensis</i>)—a known squirrel predator—and wait for the rodent to react.</p><p>Unsurprisingly, the squirrels went on high alert the moment they heard the fearsome bird’s calls, exhibiting the classic suite of vigilance behaviors. Then, as the rodents began to slowly eke their way back to baseline, Lilly played some of them another track: the chatter of several species of songbirds, gabbing away as if all was hunky dory.</p><p>These sounds are distinct from cries known as sentinel or “all clear” calls, vocalizations that evolved specifically to communicate that a known threat has passed, Tarvin says. Chatter, on the other hand, is more like blase bird babble that probably wouldn’t be happening if danger was nigh.</p>
            <figure class="richtext-image full-width"><img alt="iStock-1134938131.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-1134938131_ALtpBa0.width-800.jpg"/><figcaption><p>Good food, good conversation. Image Credit: Jennifer Coulter, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>Hearing this soothing soundtrack seemed to speed up the squirrels’ return to business as usual, compared to a second group that had been played a recording of only background noise, sans bird chatter. Both sets of rodents were probably ultimately headed toward the same fate, Tarvin says. But in the aftermath of panic, bird chatter might be a special something that puts a nervous squirrel at ease.</p><p>“This really adds something to the [scientific] literature,” MacDonald says. “Not only does [bird chatter] say there’s no predator...it tells the squirrels, ‘Now, you can really relax.’”</p><p>Of course, the timing of these events is probably a lot more variable under natural circumstances. After all, squirrels aren’t always in the vicinity of birds shooting the breeze. But ambient chatter is “free, public information” that anything within earshot could potentially take advantage of, Tarvin says. In the wild, it’s the closest squirrels can get to wiretapping their loud-mouthed feathered friends.</p><p>“Squirrels are incredibly successful,” says <a href="https://www.squirrelgazer.com/who-we-are.html">Amanda Robin</a>, a squirrel researcher at the University of California, Los Angeles who was not involved in the study. “This could be one more example of how they’re able to take advantage of things that are in their environment.”</p>
            <figure class="richtext-image full-width"><img alt="shutterstock_667418098.jpg" class="richtext-image full-width" height="529" width="800"
            src="/wgbh/nova/media/images/shutterstock_667418098.width-800.jpg"/><figcaption><p>Shh, it&#x27;s okay. Image Credit: Jud goodwin, Shutterstock</p><div class="credit"><p></p></div></figcaption>
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            <p>It’s still not clear how squirrels learn to tune in to avian chitchat. But the calls played in the study spanned about a dozen different birds, hinting at the possibility that these rodents have the cognitive flexibility to decipher similar signals from a wide range of species (including, perhaps, some of their noisiest neighbors: humans).</p><p>“This highlights how interconnected ecosystems are,” Robin says. “If you removed one species [like a bird], you might be changing the entire life of another species and not know.”</p><p>Understanding these subtle ecological networks will be essential for future conservation efforts, Lilly says. With noise pollution levels on the rise, we humans may already be covering up communication in the environment that we’re not even aware of yet.</p><p>MacDonald agrees. “Animals aren’t just paying attention to other squirrels—they’re paying attention to everything in the environment,” she says. “That’s why biodiversity is so important.”</p></div>
  

  
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<p>These nosy rodents may not speak bird-ese, per se, but they can still use avian chatter as a safety cue.</p>

Squirrels eavesdrop on bird chatter to tell when a threat has passed





  
      <div class="rich-text"><p>Apart from the whole bird versus mammal thing, crows and humans have a lot in common. Like us, these clever corvids have excellent memories and a penchant for puzzles. They can make and use tools, and move through the world in complex social groups. They’re even somewhat <a href="https://corvidresearch.blog/tag/are-crows-monogamous/">monogamous</a>—just like us.</p><p>Now, the less delightful news: Crows, too, are gluttons for junk food—and their bodies are not immune to its effects. In a <a href="https://academic.oup.com/condor/article-lookup/doi/10.1093/condor/duz040">study</a> published today in the journal <i>The Condor: Ornithological Applications,</i> scientists found that city-dwelling crows tend to have higher cholesterol than their rural cousins. The culprit, it seems, are the human-like diets they adopt, including the fatty, calorie-dense McDonald’s cheeseburgers that line many an urban alleyway.</p></div>
  

  
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      <div class="rich-text"><p>This fatty spike isn’t necessarily caws for alarm, though, and there’s not yet evidence that elevated cholesterol has a long-term impact on crow health. But the case with crows has always been complex, as these birds are among the few species that actually <i>thrive</i> in urban environments.</p><p>In the United States, the American crow (<i>Corvus brachyrhynchos</i>) effectively commands a coast-to-coast range, due in part to its plucky combination of mental acuity and apparent stomach of steel. While countryside crows are often found munching on fruits, nuts, insects, and small mammals, given the opportunity, these opportunistic omnivores will gobble up pretty much anything they can get their beaks in, including straight-up garbage.</p><p>In a lot of cases, this indiscriminate dining comes in handy: Food is food, whether it’s served on a silver platter or fished out of the sludge at the bottom of a dumpster. But the modern human diet—especially in Western countries—contains a lot of <a href="https://www.pbs.org/wgbh/nova/article/ultra-processed-foods-weight-gain/">highly processed, calorie-rich fare</a>, and the contents of city refuse are often a far cry from what these birds (or any other animal) evolved to eat.</p>
            <figure class="richtext-image full-width"><img alt="crow-3263985_1280.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/crow-3263985_1280.width-800.jpg"/><figcaption><p>Didn&#x27;t get there fast enough, bud. Image Credit: MabelAmber, Pixabay</p><div class="credit"><p></p></div></figcaption>
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            <p>For years, researchers have known that people in urban areas <a href="https://gh.bmj.com/content/4/1/e001017">tend to have higher cholesterol</a> than those in rural regions. So study author <a href="https://www.hamilton.edu/academics/our-faculty/directory/faculty-detail/andrea-townsend">Andrea Townsend</a>, a behavioral biologist at Hamilton College, wasn’t terribly surprised when an analysis of 140 American crow nestlings from Davis, California showed the same pattern.</p><p>To tie the find more directly to diet, the researchers then devised a <i>Super Size Me</i> setup with a new cohort of crows in upstate New York. During the nesting seasons of 2017 and 2018, Townsend and her colleagues spent their days tossing cheeseburgers within sight of known crow nests—bait that inevitably piqued the interest of parent birds, which hauled the greasy treats back to their young.</p><p>The experiment required a steady supply of fast food, and the team became regulars at the local McDonalds in the village of Clinton, where they’d often place orders of around 100 burgers at a time. “We got a lot of looks of shock and horror from the employees,” Townsend says. (The crows, on the other hand, “seemed delighted with the whole study design,” she says.)</p></div>
  

  
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      <div class="rich-text"><p>After several weeks on the cheeseburger diet, nestlings had more cholesterol in their blood than baby birds that hadn’t been provided with extra food. Crows only remain in the nest until they’re about a month old, after which point they get much tougher to catch, Townsend says. Because of this, it’s not clear whether these particular birds maintained higher cholesterol, or suffered any ill effects in the long term.</p><p>The fast food fix may have even <i>helped</i> the birds: Before the cheeseburgered nestlings flew the coop, they were larger and heavier. In the crow community, it’s actually a good thing to be “chubby” as a kid, Townsend says, and portly young birds tend to be healthier as adults.</p><p>This result seemed to be bolstered by another one from the nestlings the team had studied in California. During the two or three years after these crows fledged, the researchers kept tabs on them to see if having higher cholesterol at a young age impacted survival. Contrary to Townsend’s expectations, it didn’t: In broad strokes, crows from across the cholesterol spectrum seemed to fare about the same.</p><p>The reasons for this aren’t entirely clear. But while there’s a clear cutoff for <a href="https://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_cholesterol.htm">“desirable” cholesterol levels</a> in humans, no such statistic exists for our feathered friends—and having <i>higher</i> cholesterol in youth doesn’t necessarily translate to having <i>high</i> cholesterol in adulthood.</p><p>In other words, crows may simply be putting the molecule to good use. Despite its bad rap in nutrition circles, cholesterol is <a href="https://www.cdc.gov/cholesterol/about.htm">essential for animal life</a>, and forms an important structural component of cells. It’s important enough that our livers churn it out on the regular—and unusually low cholesterol levels in humans can <a href="https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/expert-answers/cholesterol-level/faq-20057952">cause health problems</a> of their own.</p><p>So when it comes to bird health and cholesterol, “there isn’t a simple answer at this point,” says <a href="https://www.binghamton.edu/biology/people/profile.html?id=aclark">Anne Clark</a>, an ecologist and crow expert at Binghamton University who was not involved in the study. But, she adds, maybe that’s to be expected. “The relationships between humans, food, and urban animals is bound to be complicated, in the same way that getting a good diet in the modern age is complicated.”</p><p>Still, the lack of negative effects in these birds shouldn’t be taken as an invitation to throw caution (or cheeseburgers) to the wind, Townsend says. The study only followed its feathered subjects for a couple years—but crows can live more than 15 years in the wild, and upwards of 50 years in captivity. Had the cheeseburger intervention or its follow-up been more prolonged, it’s possible things might have looked different, she says.</p>
            <figure class="richtext-image full-width"><img alt="crow burger 2.JPG" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/crow_burger_2.width-800.jpg"/><figcaption><p>An American crow inspects a McDonalds cheeseburger deposited by researchers in Clinton, New York. Image Credit: Andrea Townsend, Hamilton College</p><div class="credit"><p></p></div></figcaption>
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            <p>These results also won’t necessarily hold true in other species. <a href="https://sora.unm.edu/sites/default/files/journals/condor/v088n03/p0279-p0284.pdf">Sparrows</a>, <a href="https://www.jstor.org/stable/3802807?seq=1#page_scan_tab_contents">foxes</a>, <a href="https://academic.oup.com/conphys/article/1/1/cot032/365540">iguanas</a>, and <a href="https://www.sciencedirect.com/science/article/pii/S0048969717328371?via%3Dihub">turtles</a> also seem to get a cholesterol boost from urban environments, but the ultimate consequences of these changes remain mostly unclear. With their dietary flexibility, crows may be among the creatures best adapted to scarf down the occasional burger, says <a href="https://hunterlab.weebly.com/people.html">Corina Newsome</a>, a wildlife biologist and conservation ecologist at Georgia Southern University who was not involved in the study. But that won’t be the case for all animals—or even all birds, she says.</p><p>Things get even more complex when considering the impact of urbanization as a whole on animal wellbeing, says <a href="https://www.clemson.edu/cafls/faculty_staff/profiles/lanhamj">J. Drew Lanham</a>, a wildlife conservationist and ornithologist at Clemson University who was not involved in the study. While Townsend’s team didn’t find a relationship between cholesterol levels and crow mortality, one troubling trend did emerge: The more urban a bird’s habitat was, the lower its likelihood of survival.</p><p>“There’s something going on in the urban environment, either psychological or physiological, that’s having an impact on wellbeing,” Lanham says. “It makes me wonder about things like stress...and what an urban environment exacts on body and mind.”</p><p>These lingering uncertainties are perhaps all the more reason to <a href="https://www.smithsonianmag.com/science-nature/when-it-comes-humans-and-wildlife-whos-bothering-whom-180969567/">keep wildlife wild</a>, Newsome says, especially when it comes to nutrition. After all, “if it’s not healthy for us, it’s probably not healthy for them.”</p></div>
  

  
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<p>But it’s not clear whether elevated cholesterol is bad for birds.</p>

Cheeseburgers give urban crows higher cholesterol—just like us





  
      <div class="rich-text"><p>Despite their name, shy, slow-moving catsharks aren’t all that catlike—or even sharklike, really—compared to their chompier cousins of <i>Jaws</i> fame.</p><p>Running just 2 to 3 feet in length, these bashful bottom feeders spend much of their time holed up in seafloor crevices, where their intricately spotted skin camouflages them against the rocks.</p><p><a href="https://www.baruch.cuny.edu/wsas/academics/natural_science/dgruber.htm">David Gruber</a>, a marine biologist at Baruch College, puts it bluntly: “These are not the Michael Phelps of sharks,” he says.</p><p>But something about catsharks like the swell shark (<i>Cephaloscyllium ventriosum</i>) and chain catshark (<i>Scyliorhinus retifer</i>) has captivated Gruber for years—a secret power that can make even the most demure of these underwater wallflowers light up a room.</p></div>
  

  
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      <div class="rich-text"><p>Swell sharks and chain catsharks can transform the ocean’s blue light into a luminous green hue. This phenomenon, called biofluorescence, has been studied in other marine creatures that are known to convert light through the action of a well-known protein.</p><p>But as Gruber and his colleagues <a href="https://www.cell.com/iscience/fulltext/S2589-0042(19)30244-5">report</a> today in the journal <i>iScience</i>, catsharks have found their own way to glow, relying instead on an unusual class of small molecules in their skin to produce their signature shimmer. In doing so, these fluorescent fish initiate a discreet dialogue with their peers—one that might play a role in mating displays and more.</p><p>“This is a reminder that fish may look different to each other than they do to us,” says <a href="https://www.switzernetwork.org/users/natalya-gallo">Natalya Gallo</a>, a marine ecologist at the Scripps Institution of Oceanography who was not involved in the study. “When we’re thinking about marine ecology, we need to consider this landscape of light.”</p>
            <figure class="richtext-image full-width"><img alt="Biofluorescent shark Scyliorhinus retifer ©David Gruber (1).jpg" class="richtext-image full-width" height="422" width="800"
            src="/wgbh/nova/media/images/Biofluorescent_shark_Scyliorhinus_retifer_Davi.width-800.jpg"/><figcaption><p>Chain catsharks (Scyliorhinus retifer) use small molecules in their skin to convert blue light into green. Image Credit: Courtesy of David Gruber, Baruch College</p><div class="credit"><p></p></div></figcaption>
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            <p>Unlike air, water isn’t terribly good at transmitting light. By the time the sun’s rays have trickled down to the seafloor, most wavelengths have been filtered out, save for those that our eyes see as blue.</p><p>One of the most effective ways to stand out in this monochromatic world is to undergo a colorful costume change—a strategy that’s been taken up by a <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0083259">menagerie of marine creatures</a>, from jellyfish to corals. In most cases, this trick involves a protein, aptly named green fluorescent protein, or GFP, that absorbs the ocean’s abundant blue light and emits it as a far rarer shade of green. (This is totally different from bioluminescence, in which animals create their own light from scratch, or host bacteria that do it for them.)</p><p>Several years ago, Gruber led a team of researchers in <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0083259">describing how</a> the skin of swell sharks and chain catsharks <a href="https://www.nature.com/articles/srep24751">accomplishes a similar feat</a>. They also found that the sharks had evolved specially adapted eyes to match, allowing them to glimpse each other while flying under the radar of less enlightened fish (and, perhaps, nosy scientists).</p><p>For sharks, at least, fluorescence can create “high contrast in a dim environment,” says <a href="https://oceanexplorer.noaa.gov/edu/oceanage/04widder/welcome.html">Edie Widder</a>, CEO and senior scientist at the Ocean Research and Conservation Association (ORCA), who was not involved in the study.</p><p>What’s less clear, though, is how the sharks produce their green glow in the first place.</p></div>
  

  
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      <div class="rich-text"><p>Under normal white light, swell sharks are covered in splotches of tan and brown, with tiny beige spots sprinkled throughout. But when viewed through a special camera that mimics shark vision, the tan skin glows green. Brightest of all are the beige freckles, which, when illuminated, almost make the fish look like finned Christmas trees.</p><p>To home in on the source of the twinkling, Gruber recruited Baruch chemist <a href="https://www.baruch.cuny.edu/wsas/academics/natural_science/jgaffney.htm">Jean Gaffney</a> to identify chemicals more abundant in the lighter parts of swell shark skin. After a battery of procedures and tests, Gaffney was pretty sure she’d managed to extract the glowing catshark compound. But the find came with an unexpected twist: Unlike the ocean’s most famous fluorescent agent, GFP, this new molecule didn’t appear to be a protein.</p><p>This revelation put Gruber, a protein chemist, a little out of his depth. So he contacted <a href="https://chem.yale.edu/people/jason-crawford">Jason Crawford</a>, a biochemist at Yale University whose team quickly confirmed that the culprit was a small molecule—a series of them, actually. Together, the molecules comprised a metabolic pathway that processed a modified form of tryptophan, a protein building block that’s found throughout the bodies of humans and the foods we eat. A follow-up experiment revealed that the same compounds were present in the skin of chain catsharks, which are mottled with a more snakeskin-like pattern than their cousins.</p><p>Similar metabolic pathways exist in humans and many other animals, where they’re thought to play roles in immunity, brain function, and more. This versatility sets these molecules apart from proteins like GFP, Crawford says, which tend to serve only one explicit function: fluorescence. So the researchers weren’t all that shocked when they discovered that some of the catsharks’ fluorescent molecules also halted the growth of two potentially pathogenic bacterial strains.</p>
            <figure class="richtext-image full-width"><img alt="Fig 7 swell shark montage Photos by David Gruber.jpg" class="richtext-image full-width" height="914" width="800"
            src="/wgbh/nova/media/images/Fig_7_swell_shark_montage_Photos_by_David_Grub.width-800.jpg"/><figcaption><p>The swell shark (Cephaloscyllium ventriosum) is marbled with splotches of light and dark skin, speckled with spots of beige. These beige spots shine especially bright when viewed through a camera that mimics the catshark eyes. Image Credit: Courtesy of David Gruber, Baruch College</p><div class="credit"><p></p></div></figcaption>
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            <p>It’s not known what came first—the molecules’ microbe-fighting properties, or their eerie green glow. Either way, Crawford says, this likely represents a case of evolutionary co-opting, in which one set of biological tools was repurposed for a second, perhaps equally important, task.</p><p>“This study is really well done,” says <a href="https://lampichthys.com/about">Rene Martin</a>, a marine biologist studying deep-sea fish at the University of Kansas who was not involved in the study. “Biofluorescence is a field that hasn’t been as widely explored [compared to bioluminescence]...and it’s great to have a more molecular approach.”</p><p>But chemistry isn’t the whole picture, Widder points out. Researchers still aren’t entirely sure why these catsharks evolved into toothsome glowsticks.</p><p>Gruber thinks a hint might lie in the intricate patterns of light the fish give off. Shark skin is almost entirely blanketed by rough, pointed scales, and in the chain catshark, a subset of these spiny projections are studded with transparent stripes, illuminating a path like the lit aisle of an airplane. Species-specific patterns like these, Gruber says, could help sharks tell each other apart—or avoid cases of mistaken identity.</p><p>What’s more, males and females of both catshark species glow in noticeably different ways. Though it hasn’t been confirmed, Gruber says it’s possible green light functions as a sort of sexual beacon, allowing catsharks to identify or even attract potential mates. In other words, fluorescent might be kind of flirty.</p>
            <figure class="richtext-image full-width"><img alt="Catshark lightguiding denticle2 Photo by James Weaver.png" class="richtext-image full-width" height="354" width="800"
            src="/wgbh/nova/media/images/Catshark_lightguiding_denticle2_Photo_by_James.width-800.png"/><figcaption><p>The light-transmitting cells of the chain catshark (Scyliorhinus retifer), seen under fluorescence on the right. Image Credit: Courtesy of James Weaver, Wyss Institute for Biologically Inspired Engineering, Harvard University</p><div class="credit"><p></p></div></figcaption>
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            <p>Whatever catsharks are using their fluorescence for, they’re probably not alone. Biofluorescence <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0083259">evolved several times</a> in different families of fish, and is present in at least 180 marine species. And there are probably many more that have yet to show their true colors—which means catsharks will almost certainly have to share their subtle spotlight. “We don’t know how deep this goes yet,” Gruber says. “We’re just at the tip of the iceberg.” (For what it’s worth, Gruber is pretty sure that the whale shark, a catshark cousin that can weigh <a href="https://www.pbs.org/wgbh/nova/article/whale-sharks-go-without-food/">up to 20 tons</a>, is not among the luminous. He’s checked.)</p><p>“Even in this blue environment, [these sharks] have found a way to make their world more rich,” Gruber says. “I hope this calls attention to these animals, and the mysteries that are still out there.”</p></div>
  

  
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<p>Two kinds of glow-in-the-dark catsharks convert blue light to green, and now we know how.</p>

Super-shy catsharks have a weird way of lighting up





  
      <div class="rich-text"><p>If your kiwi vine isn’t producing fruit, it might be languishing under substandard care. Or maybe it’s a boy.</p><p>Let me explain.</p><p>Kiwi plants (genus <i>Actinidia</i>) segregate into two biological sexes—male and female—that are determined by X and Y sex chromosomes. Female plants, with two X chromosomes, are the fruit-bearing ones, and they need to be fertilized by the pollen of genetically XY male plants before they can produce their tangy, bright-fleshed orbs.</p></div>
  

  
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      <div class="rich-text"><p>To us humans, who also use an XY sex determination system, that might not sound all that strange. But in the world of flowering plants, where the <a href="https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.1400196">vast majority of species</a> are hermaphrodites that contain both male and female sex organs in the same individual, kiwifruit is an anomaly.</p><p>Now, an international team of researchers may have pinpointed the two genes—a dynamic duo named <i>Shy Girl</i> and <i>Friendly Boy</i>—responsible for determining a kiwi vine’s sex. And their backstory, revealed in two <a href="http://www.plantcell.org/content/plantcell/30/4/780.full.pdf">recent</a> <a href="https://www.nature.com/articles/s41477-019-0489-6">studies</a>, is quirkier than one might imagine.</p>
            <figure class="richtext-image full-width"><img alt="Actinidia_fruits.jpg" class="richtext-image full-width" height="651" width="800"
            src="/wgbh/nova/media/images/Actinidia_fruits.width-800.jpg"/><figcaption><p>Kiwifruit by species. A = <i>Actinidia arguta</i> (hardy kiwifruit), C = <i>Actinidia chinensis </i>(golden kiwifruit), D = <i>A. deliciosa </i>(fuzzy kiwifruit), E = <i>Actinidia eriantha</i>, I = <i>Actinidia indochinensis</i>, P = <i>Actinidia polygama </i>(silver vine), S = <i>Actinidia setosa</i>. Image Credit: Crowhurst et al., <i>BMC Genomics</i>, 2008</p><div class="credit"><p></p></div></figcaption>
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            <p>Only <a href="https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.1400196">about 5 to 6 percent</a> of flowering plants split themselves into separate sexes. However, many members of this exclusive club—which includes asparagus, papaya, persimmon, marijuana, and kiwi—are only distantly related, suggesting that plants ditched hermaphroditism several times throughout their evolutionary history.</p><p>This sexual switcheroo can be a powerful one, because it essentially forces single plants to mingle. With sex organs divvied up, any act of reproduction must involve two individuals, upping the chances of offspring being more genetically diverse. In the case of the kiwi, this probably helped plants rapidly adapt to a wide range of environments in its native China, says <a href="https://www.linkedin.com/in/sarah-pilkington-7155579/">Sarah Pilkington</a>, a plant geneticist and kiwifruit expert at the New Zealand Institute for Plant and Food Research Limited and author on the more recent study.</p></div>
  

  
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      <div class="rich-text"><p>But rejiggering your entire sex determination system is no small feat. To figure out how the gonadal split evolved in kiwis, a team of researchers led by <a href="https://www.hakubi.kyoto-u.ac.jp/eng/02_mem/02akagi.shtml">Takashi Akagi</a>, a plant geneticist at Kyoto University and Okayama University in Japan and author on both studies, sequenced the genomes of dozens of male and female kiwi plants.</p><p>When compared side by side, the vines’ genomes revealed that male plants contained a gene that appeared to halt the development of would-be-female reproductive parts. Because this spaying agent led to the cloaking of female gonads, Akagi and his colleagues cheekily dubbed the gene <i>Shy Girl,</i> publishing their results <a href="http://www.plantcell.org/content/plantcell/30/4/780.full.pdf">last year in the journal <i>Plant Cell</i></a><i>.</i></p><p>But even then, Akagi knew the story was likely incomplete. According to a <a href="http://evol.bio.lmu.de/_teaching/Seminar_EvolSex/Charlesworth%20and%20Charlesworth%20-%201978%20-%20A%20Model%20for%20the%20Evolution%20of%20Dioecy%20and%20Gynodioecy.pdf">decades-old theory</a>, <i>Shy Girl</i> should have a partner in crime—a second, male-gonad-promoting gene to complement its female-gonad-suppressing effects.</p><p>In this evolutionary model, male and female gonads develop like a pair of light switches, operating side by side. Turn both on, and you’ll get an entire species of hermaphrodites. Transitioning to a two-sex system requires two genetic changes: one that turns off the female switch in males, and another that shuts down the male switch in females. <i>Shy Girl</i> was only enough to accomplish the first.</p><p>To find the missing link, Akagi, Pilkington, and their colleagues teamed up to wrangle a new set of kiwi vines. This time, the researchers went through the plants’ genomes with a finer-toothed comb, hunting for genes that were expressed at higher levels in males during a critical point in kiwi sexual development. Sure enough, the search bore fruit, revealing a hunk of DNA that actively encouraged male reproductive parts to develop. The team named the gene <i>Friendly Boy—</i>the etymological yang to <i>Shy Girl</i>’s yin.</p>
            <figure class="richtext-image full-width"><img alt="iStock-537403487.jpg" class="richtext-image full-width" height="529" width="800"
            src="/wgbh/nova/media/images/iStock-537403487.width-800.jpg"/><figcaption><p>When looking into the sex lives of kiwifruit, things can sometimes get hairy. Image Credit: nata_vkusidey</p><div class="credit"><p></p></div></figcaption>
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            <p>But as the researchers report <a href="https://www.nature.com/articles/s41477-019-0489-6">today in the journal <i>Nature Plants</i></a><i>, Friendly Boy</i> didn’t work exactly like <i>Shy Girl</i> did. While <i>Shy Girl</i> put the brakes on female development by shutting <i>off</i> a switch, <i>Friendly Boy</i> exerted its effects because it <i>was</i> an “on” switch. The critical second genetic change, then, was actually the loss of <i>Friendly Boy</i> from the female kiwi genome: Rather than fussing over which way the male switch was turned, female plants dispensed with the entire contraption.</p><p>There’s a flip side to this, too. Because only two roadblocks exist between hermaphroditic kiwis and unisex kiwis, messing with this delicately reconfigured system is kind of, well, low-hanging fruit.</p><p>Over the years, kiwi farmers have discovered that at least one species—<i>Actinidia deliciosa,</i> an especially hairy cultivar commonly sold in stores—can be bred to yield hermaphrodites, in the form of genetically XY vines that still produce shrunken female fruits. When the researchers scoured these hermaphrodites’ DNA, they discovered that the plants had discarded <i>Shy Girl</i> from their genomes, allowing female gonads to emerge. (Presumably, the converse of this—a plant with a broken copy of <i>Friendly Boy—</i>would leave a vine in a sexual no plant’s land, yielding a “neutered” male, Akagi says.)</p><p>The final nail in the coffin, Pilkington says, was one last experiment in which the team plunked a copy of <i>Friendly Boy</i> into the genome of a fast-flowering female kiwi plant. Within months, the seedlings had sprouted hermaphroditic flowers—and, after a round of self-pollination, the plants even began to yield small but fertile fruit.</p>
            <figure class="richtext-image full-width"><img alt="kiwi hermaphrodite combo.jpg" class="richtext-image full-width" height="276" width="800"
            src="/wgbh/nova/media/images/kiwi_hermaphrodite_combo.width-800.jpg"/><figcaption><p>Left: A self-pollinating kiwifruit, created when researchers added a copy of <i>Friendly Boy</i> to a female plant. The fruits shown are fertile. Right: A female plant that was only able to bear fertile fruit when pollinated by another vine. Image Credit: Akagi et al., Nature Plants, 2019</p><div class="credit"><p></p></div></figcaption>
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            <p>“This team has done beautiful science,” says <a href="http://www.celinecaseys.ch/">Céline Caseys</a>, a plant biologist at the University of California, Davis who was not involved in either study. “They knew the [first study] was just half the story...and seeing the full story come together is really nice.”</p><p>The study’s findings add to the growing list of unusual strategies plants use to split up the sexes. While <a href="https://www.nature.com/articles/s41467-017-01064-8">asparagus</a> seems to adhere to a somewhat similar system, <a href="https://science.sciencemag.org/content/346/6209/646.long">persimmons</a> don’t. Clearly, there’s more than one path to unisexuality, and so far, all appear to be ripe for the picking.</p><p>These results also hint at the possibility of genetically manipulating <i>Shy Girl</i> and <i>Friendly Boy</i> in kiwi cultivars to generate self-pollinating, hermaphroditic vines, Akagi says. In theory, this could give breeders a simple way to mass-produce the fruit.</p><p>Several plants, including common cultivars of grapes and papaya, are already purposefully bred to yield hermaphrodites. Though none of these modifications have involved direct gene editing so far, this study shows it’s possible, says <a href="https://sib.illinois.edu/profile/rayming">Ray Ming</a>, a plant biologist at the University of Illinois at Urbana-Champaign who was not involved with the study.</p><p>All this highlights just how loose sexual delineations can be—even from a kiwifruit’s point of view. Something to chew on the next time you slice open one of these bad boys (er, girls).</p></div>
  

  
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<p>These two genes are all it takes to determine the sex of a kiwifruit.</p>

How kiwi plants’ Shy Girls and Friendly Boys helped them evolve separate sexes





  
      <div class="rich-text"><p>It’s a scary world out there.</p><p>That’s why yellow-legged gulls (<i>Larus michahellis</i>) have figured out a clever way to gauge their surroundings while still encased within their speckled eggs. Before they hatch, these birds can tune in to the alarm calls of their parents, who emit a series of signature squawks when they sense the presence of ravenous, chick-chomping mink.</p><p>These chicks then take Mom and Dad’s warnings to heart—and after hatching, they behave in ways that may help them avoid getting eaten.</p><p>But even before busting out of their shells, these little gulls do something else unusual.</p></div>
  

  
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      <div class="rich-text"><p>After hearing their parents’ calls of distress, embryos prepping for potential predators will toss and turn in their eggs. The resulting vibrations, it seems, are then picked up by their unhatched nestmates, which, when they emerge, look and act similarly to their siblings—even if they never got the original memo.</p><p>It’s a bizarre game of avian telephone, and researchers still aren’t completely sure how the underlying process works. But this strikingly sophisticated display of communication, reported in a <a href="https://www.nature.com/articles/s41559-019-0929-8">study</a> published today in the journal <i>Nature Ecology &amp; Evolution,</i> reinforces the notion that eggs are more than passive embryonic vessels. The findings also suggests that, by picking up subtle signals from siblings, chicks-to-be can prep for hardship without actually having to experience it firsthand.</p><p>“Any information an animal gleans from its environment...will help it prepare for the world it’s about to be born into,” says <a href="http://calisilab.ucdavis.edu/">Rebecca Calisi Rodríguez</a>, a bird behavioral biologist at the University of California, Davis who was not involved in the study. “But the mind-blowing thing here is that there’s communication between siblings...in a way that changes how all of them develop.”</p>
            <figure class="richtext-image full-width"><img alt="combo pip.jpg" class="richtext-image full-width" height="599" width="800"
            src="/wgbh/nova/media/images/combo_pip_copy.width-800.jpg"/><figcaption><p>Yellow-legged gull chicks. Adults will lay eggs days apart, resulting in clutches of embryos at different stages of development. Image Credit: Jose C. Noguera, University of Vigo</p><div class="credit"><p></p></div></figcaption>
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            <p>This isn’t the first time researchers have eavesdropped on animals chattering at their unborn offspring. In 2016, Deakin University researchers <a href="https://www.deakin.edu.au/about-deakin/people/mylene-mariette">Mylene Mariette</a> and <a href="https://www.deakin.edu.au/about-deakin/people/kate-buchanan">Katherine Buchanan</a> discovered that rising temperatures can prompt adult zebra finches to <a href="https://science.sciencemag.org/content/353/6301/812">belt out ballads</a> that broadcast the warm conditions to their eggs, which in turn hatch chicks better adapted to the heat. Others have shown that siblings, too, can convey prenatal messages to their nestmates—and several <a href="https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1439-0310.1999.10512489.x">birds</a>, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4796811/">reptiles</a>, and <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(18)31490-8">insects</a> are known to coordinate hatching times through cues passed from egg to egg.</p><p>But neither of these processes is well understood, and they’ve never been linked together like this in the same species, says study author <a href="https://sites.google.com/view/josecnoguera/home">Jose Noguera</a>, a behavioral ecologist at the University of Vigo in Spain.</p></div>
  

  
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      <div class="rich-text"><p>So Noguera and his advisor, <a href="http://avelando.webs.uvigo.es/alberto.html">Alberto Velando</a>, decided to see if eggs could act as yolky intermediary in ferrying crucial intel—like the presence of a predator—from parent to offspring to sibling.</p><p>Such a familial relay might seem redundant, since all the eggs in a single nest should be exposed to the same cries. But some birds, like the yellow-legged gull, lay their eggs several days apart, which means each embryo in a given nest is at a different point along its developmental trajectory.</p><p>Because hearing crystallizes relatively late in development, older siblings are better equipped to receive their parents’ vocal warnings. Touch, on the other hand, is an early-emerging sense—which could make inter-egg vibrations a way to get a hard-to-hear message across to the junior members of a clutch, Noguera says.</p><p>To test this theory, Noguera and Velando gathered 90 second-laid yellow-legged gull eggs—the natural middle children of clutches—and divvied them up into 30 trios. During each day of the eggs’ last week of development, the researchers briefly exposed two of the eggs in each clutch to either recordings of adult alarm calls or static from a speaker, then returned them to incubate with an undisturbed foster sibling.</p><p>Clutches whose eggs weren’t privy to the prenatal panic yielded uniformly carefree chicks. But embryos that had regularly encountered alarm calls took longer to emerge from their eggs—and though they eventually hatched, these chicks never fully came out of their figurative shells. Their blood brimmed with stress hormones, and they were quieter and quicker to hide when they heard more of the adults’ cautionary caws. There were even changes in how the chicks broadly expressed different sets of genes.</p><p>And the hatchlings didn’t just internalize these subliminal messages: They passed them on to their uninformed siblings, too. After listening to squawks of distress, eggs shook and shimmied, knocking up against their nestmates—which then made moves of their own.</p>
            <figure class="richtext-image full-width"><img alt="35805201206_14cce4a62f_o.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/35805201206_14cce4a62f_o.width-800.jpg"/><figcaption><p>A trio of yellow-legged gull chicks in Galicia, Spain. Image Credit: Contando Estrelas, flickr</p><div class="credit"><p></p></div></figcaption>
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            <p>These secondhand signals, Noguera says, were enough to seal the fates of the unexposed chicks—even in the absence of direct auditory input. From blood to behavior, these eggs and the hatchlings they bore were identical to their stressed-out siblings by every metric measured.</p><p>“It’s not just about what happens to you during development,” Noguera says. “It matters what happens to your siblings, too.”</p><p>Because the researchers didn’t follow the chicks into adulthood, it’s difficult to say just how adaptive these behavioral and physiological changes were, says Mariette, who wrote a <a href="https://www.nature.com/articles/s41559-019-0955-6">commentary</a> to accompany the study, which she wasn’t involved in. (The changes also probably come with costs, she notes: For instance, chicks exposed to alarm calls—both directly and by proxy—grew slower and were smaller than their counterparts.)</p><p>However, the sophisticated demonstration of clutchmate coordination still sets this paper apart, Mariette adds. Unhatched chicks aren’t just <i>aware</i> of the world around them; they’re able to convey information about it, too. “Embryos are really not as isolated as we tend to think of them,” she says.</p>
            <figure class="richtext-image full-width"><img alt="3 chicks.JPG" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/3_chicks.width-800.jpg"/><figcaption><p>Yellow-legged gull chicks huddled in their nest. Image Credit: Jose C. Noguera, University of Vigo</p><div class="credit"><p></p></div></figcaption>
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            <p>Fussy bird parents might deliberately chirp at their eggs to convey information. But Noguera cautions that the study’s findings don’t necessarily mean that unhatched siblings are engaging in any kind of <i>intentional</i> conversation among themselves. Rather, there’s a good chance these eggs are just sponging up whatever intel they can get. And though he hasn’t yet shown it for this species, Noguera thinks there are probably other cues, such as smells, that might play a role in the prenatal avian milieu.</p><p>That might not be all that surprising, given how sensitive other <a href="https://www.pbs.org/wgbh/nova/article/prozac-may-transcend-generations/">embryos</a> (including those of <a href="https://www.pbs.org/wgbh/nova/article/male-twin-might-change-the-trajectory-of-a-womans-life/">humans</a>) are to their environments. But when it comes to the nuclear family, knowledge may flow more freely than once thought. The routes it takes probably aren’t always direct—and maybe that’s the point.</p><p>“We’re subconsciously gathering information from each other all the time,” Calisi Rodríguez says. “There’s that saying: ‘By failing to prepare, you are preparing to fail.’ By having these particular capabilities, these organisms are preparing to succeed.”</p></div>
  

  
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<p>Even while still in their eggs, baby birds can hear their parents’ alarm calls. They then pass the message along to unhatched siblings so the entire clutch emerges aware of the dangers ahead.</p>

Quivering bird eggs prep each other for predators before they hatch





  
      <div class="rich-text"><p>In 2013, a deadly swine virus popped up on a handful of U.S. pig farms and quickly spread to 30 states. Over the next year, it wiped out around 10 percent of the U.S. pig population, and <a href="https://www.nationalhogfarmer.com/animal-well-being/economic-impacts-pedv">pork prices jumped.</a></p><p>This was the first appearance of porcine epidemic diarrhea virus (PEDV) in the United States. And although this particular outbreak was mostly contained in 2014, the virus remains a lingering threat to pig farms: An outbreak can cost a farm about $300,000 once dead pigs have been replaced and barns disinfected.</p><p>The virus, which does not affect humans, is spread through pig feces. Scientists still don’t understand exactly what triggers, or perpetuates, an outbreak. But that may be changing.</p></div>
  

  
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      <div class="rich-text"><p>After the initial outbreak, North Carolina State University epidemiologist <a href="https://cvm.ncsu.edu/directory/machado-gustavo/">Gustavo Machado</a>, along with colleagues from the University of Minnesota and Brazil’s Universidade Federal do Rio Grande do Sul, set out to study PEDV in sow farms across the United States. Using data on the virus’ prevalence in farms, pigs’ movements between farms, and environmental factors like wind speed and temperatures, they developed an algorithm to predict PEDV outbreaks. They used data from 2014 to “predict” outbreaks on a week-by-week basis, testing their results against what had actually unfolded each week.</p><p>In a <a href="https://www.nature.com/articles/s41598-018-36934-8">study</a> published in January in the journal <i>Nature</i>, Machado’s team showed that its algorithm was able to predict whether a PEDV outbreak would occur during a given one-week period with about 80 percent accuracy. They also determined that the movement of pigs between farms was the most important factor in the spread of the virus, but there may also be a risk of airborne spread.</p><p>“What we know is about 75 percent of the PEDV outbreak is reasoned by the movement of animals and the proximity with other farms,” Machado says. Pigs carrying PEDV can infect both their barn mates and pigs at nearby farms.</p><p>The virus infects the cells that line pigs’ small intestines, causing severe diarrhea and dehydration. The symptoms come on quickly and run a short—and sometimes severe—course. Piglets younger than a couple weeks old are most vulnerable, and often die from dehydration, diarrhea, and vomiting.</p><p><a href="https://www.vetmed.wisc.edu/people/kbernard/">Kristen Bernard</a>, a virologist at the University of Wisconsin-Madison’s School of Veterinary Medicine who was not involved in the latest study, says <a href="https://journals.sagepub.com/doi/full/10.1177/1040638713501675?url_ver=Z39.88-2003&amp;rfr_id=ori:rid:crossref.org&amp;rfr_dat=cr_pub%25253dpubmed">genomic sequencing studies</a> of PEDV suggest it originated in from a viral strain in China in 2012. <a href="https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0194509&amp;type=printable">Experts</a> suggest that PEDV may have spread to the U.S. through animal feed ingredients from China.</p><p>“It wouldn’t have been carried in the wind or water or anything like that,” Bernard says of the first U.S. outbreak. “And the fact that [initial PEDV infections] happened almost within days of each other, it’s very unlikely that it was transferred from farm to farm.” But, Bernard says, concrete evidence that PEDV came from China is still lacking.</p></div>
  

  
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      <div class="rich-text"><p>A vaccine for the virus exists, but it isn’t 100 percent effective. The vaccine does boost the herd immunity of piglets, Machado says, but researchers have found traces of PEDV in piglet fecal samples from farms where vaccination occurred.</p><p>This could be because of how the vaccine is administered, Machado says: Veterinarians vaccinate sow mothers for PEDV rather than injecting piglets directly. Mothers pass antibodies against the virus to their offspring through their milk, which should protect them from infection. But this doesn’t always pan out.</p><p>“They have immunity, but maybe it’s not enough,” Machado says of the piglets. “What we really don’t understand is if the immunity is enough to protect for a new outbreak.”</p><p>Machado says additional measures, like installing air filters, can potentially reduce the circulation of the virus. Meanwhile, his lab continues to gather data weekly from 50 percent of U.S. sow farms to model the virus’ spread.</p><p>Based on the lab’s data, Machado predicts a 10 percent decrease in PEDV in the next two years.</p><p>The swine farms that participate in Machado’s study can receive an algorithm-based prediction of any upcoming outbreaks of PEDV and other diseases.And Machado’s team is developing an online portal in which farmers can check to see if their farm is within a PEDV outbreak-expected zone. The researchers believe this will encourage precautionary measures and enable farmers to address any PEDV outbreaks immediately.</p><p>Machado also hopes to figure out why PEDV outbreaks still occur in regions where virus immunity seems to be high. “We don’t know,” he says. “Maybe the virus is inside the farm circulating at low prevalence and then something happens, and then we have [an] explosion of the virus again.”</p><p>To find answers, he and his team aim to continue to study PEDV and model its spread for another five or 10 years. Currently, they are looking into other factors that might be associated with the virus spread, including the movement of feed mill trucks into farms.</p><p>Epidemiological models like Machado’s, Bernard says, extend beyond PEDV. Analyzing pigs’ movement and population as well as factors like food and water contamination, “can be really applicable to lots of different diseases,” she says. “That’s what’s useful about these kinds of epidemiological models,” she continues. “It’s to help us know what to do in the face of a new outbreak.”</p></div>
  

  
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<p>A swine virus that appeared in the U.S. in 2013 has proven hard to track. But an algorithm might help researchers predict the next outbreak.</p>

This algorithm is predicting where a deadly pig virus will pop up next





  
      <div class="rich-text"><p>If you’re an organism with a hankering for flesh, a few things can come in handy. Fast feet, for one, to give chase, and maybe some claws and a sharp set of teeth. Good vision doesn’t hurt, either—especially when it’s teamed up with a keen nose and big, sensitive ears.</p><p>Unfortunately, the carnivorous Venus flytrap (<i>Dionaea muscipula</i>), which dines on bugs and spiders to compensate for the nutrient-poor soil of its natural wetland environment, has none of these lethal assets at its disposal.</p><p>But there’s no need to pity these predatory plants: An exquisite sense of touch is all it takes for Venus flytraps to snare their tiny prey. That’s all thanks to the sensory capabilities of a few stiff, sensitive hairs poking out from the inner surfaces of their mouth-like leaves—each tuned to discern the infinitesimally small shudders of an insect on the go. Now, scientists have finally put numbers to just how perceptive these trigger-happy hairs can be.</p></div>
  

  
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      <div class="rich-text"><p>A <a href="https://www.nature.com/articles/s41477-019-0465-1">study</a> published today in the journal <i>Nature Plants</i> shows that Venus flytrap hairs are sensitive enough to detect critters that weigh as little as 3 milligrams—less than a typical sesame seed. While this threshold may exclude the most petite of prey species, having a size cutoff may actually help the plant avoid meals too small to be worth the trouble.</p><p>When vacant, a Venus flytrap leaf resembles an open pairs of jaws. In reality, each trap is an entire digestive tract collapsed into a single, bi-lobed pouch, rimmed with fang-like protrusions. Studding the inside of the trap are a handful of thin, rigid hairs, each attached to a flexible base that can register the movements of the rod above—a bit like a joystick.</p><p>This unusual setup allows the hairs to function like tripwires. When something bumps up against them, electrical signals spread through the trap’s leafy lobes. Digestion then proceeds in a series steps: First, the trap slams shut; then, it hermetically seals. Eventually, the now-airtight chamber will flood with flesh-melting fluid, transforming whatever’s inside into sticky sludge.</p><p>Once this process begins, it can take over a week for the trap to reopen—making mistakes very costly.</p>
            <figure class="richtext-image full-width"><img alt="Venus_Flytrap_showing_trigger_hairs.jpg" class="richtext-image full-width" height="545" width="800"
            src="/wgbh/nova/media/images/Venus_Flytrap_showing_trigger_hairs.width-800.jpg"/><figcaption><p>The inside of a Venus flytrap trap is studded with a small handful of thin, stiff hairs that can be triggered by touch. Image Credit: Noah Elhardt, Wikimedia Commons</p><div class="credit"><p></p></div></figcaption>
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            <p>Luckily, the Venus flytrap has evolved a few safeguards to avoid responding to false alarms like breeze-borne debris, or the pitter-patter of intermittent raindrops. Three years ago, a team of researchers led by <a href="https://www.biozentrum.uni-wuerzburg.de/en/bot1/research/prof-dr-rainer-hedrich/">Rainer Hedrich</a>, a plant physiologist at the University of Würzburg in Germany, discovered that traps can <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(15)01501-8">“count” the number of times their hairs are nudged</a>. Each bump triggers its own electrical impulse—and the more times the hairs are touched in a row, the further along the path of consumption the plant will progress. Two touches, and the two halves of the leaf come together in a loose cage; a third zippers them tightly shut. A few more, brought on by the catch struggling within, and the whole contraption morphs into an acidic stomach, liquifying its contents.</p><p>Before any of this can happen, though, a trap’s hairs need to know when it’s appropriate to sound the alarm. “It was a simple question,” says study author <a href="https://wueaddress.uni-wuerzburg.de/person/23336">Sönke Scherzer</a>, who conducts research under Hedrich’s supervision. “But we just wanted to know how sensitive these hairs really are.”</p></div>
  

  
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      <div class="rich-text"><p>To define the limits of flytrap touchiness, Scherzer and his colleagues hooked a series of plants up to a computer that monitored their electrical activity. They then used a small, motorized device to flick the trap’s hairs, all the while looking for the subtlest movements sufficient to trigger a response.</p><p>It didn’t take much. For a signal to be sent, a tilting hair had to meet three criteria: It needed to bend more than 2.9 degrees, move fast enough to traverse at least 3.4 degrees within the span of a second, and feel a force of at least 29 micronewtons (roughly equivalent to being stepped on by a three-milligram bug, like a small mosquito).</p><p>These numbers, Scherzer says, matched up nicely with what the hairs experienced when the researchers allowed them to be trampled by a colony of ants—a common meal for wild flytraps.</p><p>Though several of the team’s findings are pretty intuitive, their paper is the first to quantitatively assess how these hairs are triggered, says <a href="https://biology.wustl.edu/people/barbara-pickard">Barbara Pickard</a>, an expert in plant sensory physiology at the Washington University in St. Louis who was not involved in the study. “Plant mechanosensing [response to detection of touch] is far more generalized and sensitive than people realize,” she says.</p><p>Not all traps are created equal, however. Each Venus flytrap hosts several sets of “jaws” of different sizes—and they don’t appear to behave in the same way. In the study, the researchers found that larger traps contained hairs that were both thicker at the base and less sensitive than those in smaller traps.</p>
            <figure class="richtext-image full-width"><img alt="iStock-118316941.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-118316941.width-800.jpg"/><figcaption><p>On a Venus flytrap, bigger traps have less sensitive trigger hairs, biasing them toward larger prey. Image Credit: Jim1123, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>From a physical standpoint, this simply reflects the fact that bulkier hairs are more difficult to bend. But there may be an evolutionary impetus behind this adaptation as well, points out <a href="https://laurahamonsite.wordpress.com/">Laura Hamon</a>, a Venus flytrap researcher at North Carolina State University who was not involved in the study.</p><p>While the teeniest traps can still get a nutritious meal out of insects and spiders weighing only a couple milligrams, it may be less advantageous for larger traps to invest in such puny portions. The higher threshold of big traps, then, might function as a precaution that prevents them from biting off less than they can chew, Hamon says.</p><p>Pickard supports the notion of size selection, highlighting the work of plant biologists <a href="http://www.hartmeyer.de/">Siegfried Hartmeyer</a> and <a href="https://www.researchgate.net/profile/Stephen_Williams21">Stephen Williams</a>, which indicates that Venus flytraps have an entire suite of traits to help them avoid unsatisfying meals. “Closing and reopening the trap takes a lot of the leaf’s available energy,” she says. “So catching small prey can be a net loss.”</p><p>According to Hartmeyer and Williams’ research, which is currently being submitted for peer-reviewed publication, the plants may use specialized scent glands to lure especially tiny prey, like certain types of ants, to the edges of their traps and away from the trigger hairs. Even after the leaf shuts, bugs small enough to slip out of the leaf’s gap-toothed grin are able to escape before the trap seals completely.</p>
            <figure class="richtext-image full-width"><img alt="DSC09485 copy.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/DSC09485_copy.width-800.png"/><figcaption><p>Even after a trap first closes, it doesn&#x27;t seal completely shut until its hairs are triggered again. Small prey can escape through the sparsely-spaced prison bars. Image Credit: Courtesy of Sönke Scherzer, University of Würzburg</p><div class="credit"><p></p></div></figcaption>
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            <p>All this goes to say that Venus flytraps may be even more calculating killers than once thought. “Plants are a lot more complex than we give them credit for,” says <a href="https://pages.wustl.edu/haswell/people/angela-schlegel">Angela Schlegel</a>, who studies mechanical signals in plants at Washington University in St. Louis, but was not involved in the study. “This paper is a highlight of how we can study that complexity.”</p></div>
  

  
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<p>Good news for bugs that weigh less than a sesame seed.</p>

Topic: Nature

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