Citizen Scientists Dig Up the Truth about Decomposing Dung

The amount of cow dung plopped into the world every day is almost unthinkable, but Tomas Roslin is thinking about it.

"We can regard it as either an immense waste problem or an enormous ecosystem service," he says. He means that what starts out as a turd in a field turns into a wealth of nutrients for plants—assuming it can make its way below ground. So understanding how dung gets broken down can help us ensure an ecosystem is running smoothly. To address such a messy, large-scale question, Roslin recruited a big mess of young volunteers.

Roslin is an ecologist at the University of Helsinki, and he found his citizen scientists through the Finnish 4H Federation. In all, 79 volunteers signed up, ranging from 10 to 27 years old (most were under 20). They agreed to sample 82 cattle farms that spanned Finland nearly from end to end.

From each farm, the volunteers collected 20 liters of "fresh dung" in late spring or early summer. They divided their dung into 15 pats (using an official dung measurer that had been provided to them) and put the pats back onto cow pastures. Some of the manmade cow patties were left open to the air, while others were covered with cages of coarse or fine mesh to keep out certain insects.

Roslin and his coauthors were especially interested in large dung beetles called dor beetles. In some cases they prevented dor beetles from burying the dung (as the beetles enjoy doing) by putting mesh underneath the patty, and in other cases a full wire cage kept dor beetles from getting into the dung at all. Smaller insects were kept out with finer mesh cages, and earthworms were blocked from the dung by putting a layer of cloth underneath it.

Volunteers weighed the dung piles periodically over the next two months to see how much was left of them. As the summer went on, the patties dried out and were broken down by whatever insects could reach them, as well as by microbes that couldn't be kept out. (Only 73 farms were left in the final analysis, since a few sites were lost to "lack of sufficient commitment by the volunteer" and others to "cows trampling on the experimental pats.")

The results showed that 13 percent of dung decomposition is done by insects. Microbes and rainstorms take care of the rest. The farther north you are in Finland, the more slowly your dung will disappear, perhaps because cooler weather slows bacterial growth.

Each added barrier around the dung made it decompose a little more slowly, showing that all the groups of insects were helping to break it down. But the biggest contribution came from dor beetles. This was in line with what previous, small-scale research had shown—but his network of citizen scientists let Roslin confirm that dor beetles are equally important all across Finland.

It matters because "our dor beetles are not doing that well," Roslin says. Out of three species in Finland, one has gone regionally extinct and another is on the decline. Knowing how important the dor beetle is to healthy farms gives Finland more reason to keep it alive.

Additionally, Roslin says, "just figuring out the basics of how the system works" is critical. In the United States, most cattle waste goes into manure lagoons, where beetles or ecosystems don't really enter the equation. But when waste is returned to the soil, Roslin says, "we need to understand who is behind it." He points out that cattle were initially brought to Northern Europe in part to fertilize the fields.

"We love citizen science," Roslin declares. He and his lab have previously organized citizen investigations of dung beetles and gall-wasps, and they're now working with volunteers to study the hermit beetle Osmoderma barnabita. "The volunteers involved have come to appreciate completely new aspects of their own environment," he says.

There are some drawback to the approach, of course —experiments have to be kept simple, and sometimes a volunteer loses interest or flattens a cow patty. But by pairing small-scale lab research with large citizen projects, Roslin says, "we have managed to collect scientific data sets unachievable by relying on professional biologists."

Riikka Kaartinen, Bess Hardwick, & Tomas Roslin (2013). Using citizen scientists to measure an ecosystem service nationwide. Ecology DOI: 10.1890/12-1165.1

Images: top Timo Marttila/Satakunnan Kansa; bottom Riikka Kaartinen.

Found: A Rotten-Smell Button in the Brain

Window or aisle? Hamburger or hot dog? Bouquet of flowers or rotting flesh? Not all your preferences are up to you—some have been hammered into your genes by evolution.

If you're an average human, you avoid the smell of decay. It signals unsafe food and the threat of infection or disease. Other animals run toward the stench of a stale carcass, maybe because they're flies and it signals a place to lay their eggs.

Whether they love it or hate it, animals identify the scent of rot from two signature molecules. German doctor Ludwig Brieger discovered these molecules in the late 1900s; in English, they're rather cutely named "cadaverine" and "putrescine." Bacteria create the two culprits by breaking down down amino acids in animal bodies. Not solely the sign of a rotting carcass, cadaverine and putrescine also show up in urine and bad breath.

Despite the importance of these smells (or avoiding these smells) in animals' lives, no one had found receptors for these molecules—that is, the locks to which the molecules are keys. Scent receptors are attached to one end of a neuron inside the nose (or whichever body part an animal smells with); when a certain chemical wafts up the nose and latches onto the receptor, a signal travels along the neuron to the brain at the other end. Researchers at the University of Cologne in Germany and Harvard University think they've found one of those receptors for rot.

The authors, led by the University of Cologne's Ashiq Hussain, studied zebrafish, which are commonly used to model the sense of smell in vertebrates. First they checked to make sure zebrafish respond to the smell of decay. When they put putrescine and cadaverine into a tank, zebrafish swam to the other end, showing they feel the same way we do about these smells. When the authors plugged the zebrafishes' little nostrils with glue, the fish were no longer bothered by the odor.

The researchers searched for a receptor in a family of proteins called TAARs (trace amine-associated receptors). Related receptors in rodents are thought to detect other unpleasant odors that come from living things. Zebrafish make 112 different kinds of these receptors, but the molecules that attach to them hadn't been found yet.

After testing 93 smelly chemicals on representative zebrafish TAARs, the authors found a match: cadaverine turns on a receptor called TAAR13c. But could the receptor detect cadaverine in real life, and not only when it was dripped on in purified form by a scientist? To test it, the researchers used an extract of dead fish. When exposed to liquid made from a recently deceased zebrafish, the receptors didn't respond. Liquid from a week-old, rotten fish carcass, though, easily activated the receptor—even when diluted to 1 part in 1,000.

Finding a receptor for cadaverine means scientists now understand a little bit more about how the vertebrate brain responds to awful smells. The receptor protein itself "will not be similar in humans, because mammals do not have close relatives of this zebrafish receptor," says Sigrun Korsching, the paper's senior author. Still, she adds, "There are very few cases where you can show activation of a single receptor leads to a behavioral response." Studying how the zebrafish's neurons respond to cadaverine could lead to a better understanding of how animals process all kinds of odors, whether they enjoy them or not.

Image: by Bill Gracey (via Flickr)

Ashiq Hussain, Luis R. Saraiva, David M. Ferrero, Gaurav Ahuja, Venkatesh S. Krishna, Stephen D. Liberles, & Sigrun I. Korsching (2013). High-affinity olfactory receptor for the death-associated odor cadaverine. PNAS DOI: 10.1073/pnas.1318596110

Note: This post has been edited from an earlier version.

Fungus-Farming Beetles Start Tending Their Crop as Babies

Inside the stems of Japanese bamboo plants, tiny farmers are working in secret. They tend to their crop of fungus, growing it in plump white clusters on their walls for eating, all while sealed safely away from the rest of the world. They begin farming the day they hatch—and when they retire, tuck some of their crop into their pockets to pass on to the next generation.

The farmer is Doubledaya bucculenta, a species of lizard beetle. Many social insects (those that live in colonies) are well-known farmers. Leafcutter ants, for example, cut up all those leaves to feed to their own fungus crop. But farming in nonsocial insects, like the loner lizard beetles, is more mysterious.

Wataru Toki of the University of Tokyo has been gradually uncovering the farming habits of D. buccalenta. Last year, Toki and other researchers announced that the beetle grows a certain kind of yeast (which is a fungus) inside bamboo plants. Each spring, female beetles come to bamboo stems, chew a hole through their hard walls, drop a single egg inside, and then seal the cavity back up. Bamboo stems have hollow sections separated by solid nodes. Inside this protected home, the egg hatches into a larva. The walls of its home end up covered in white fungus, which the larva eats.

Once it's grown into an adult, the beetle chews its way back out of the bamboo and into the world. But female beetles, the researchers found, carry a little bit of their yeast crop with them. They store it in a kind of pocket built into the ends of their abdomens. Is this stash somehow passed on to the next generation of eggs?

To find the answer, Toki and others carried out a number of experiments, including slicing bamboo stalks in half and videotaping the egg-laying process from the inside. After the mother beetle hacks into the plant (she has an asymmetrical head, which Toki suspects somehow helps her crack the tough bamboo), she turns around and sticks an organ called her ovipositor through the hole. She extrudes a single long, tubular egg, then makes several squeezing motions with her ovipositor before sealing the hole back up with bamboo fibers.

This squeezing action seems to deliver the yeast from the mother's pocket into the bamboo plant. The researchers found yeast cells concentrated on the end of the egg and at the sealed-up bamboo hole. Left alone, this yeast can grow into a meager colony. But when the egg hatches, the larva emerges from the yeasty end of the egg and begins to wriggle around its home. Soon, lush yeast colonies sprout in its path.

In other words, "The larvae actively spread the yeast," Toki says. Mothers pass down the crop to their offspring, and larvae start nurturing it as soon as they hatch. For the beetles, farming is a family business.

Toki says it's still not known how mother beetles collect yeast in their pockets. "However, it is clear that they get the yeast before they leave the home—bamboo cavity—where they grew up." Next, Toki hopes to figure out how D. buccalenta prevents other microorganisms from invading its yeast farms. They may not be social, but the beetles have plenty to tell us.


Image: Toki et al.

Wataru Toki, Yukiko Takahashi, & Katsumi Togashi (2013). Fungal Garden Making inside Bamboos by a Non-Social Fungus-Growing Beetle. PLOS ONE DOI: 10.1371/journal.pone.0079515

Schrödinger's Turtle: How Observing Ocean Animals Can Harm Them

We rely on roving ocean creatures to fetch us all kinds of data we couldn't get otherwise. Carrying cameras or GPS units or sensors glued to their bodies, marine animals collect data for human scientists about the health of ocean ecosystems or how their own species migrate. Yet lugging our equipment through the sea may be harder for these creatures than we realize. By tagging them, we might be slowing down or even harming the same species we're trying to preserve.

When scientists tag birds, the authors of a new paper in the journal Methods in Ecology and Evolution explain, they follow the "five percent rule": any transmitters they attach to a bird must be less than five percent of its body mass. This ensures the animal can still take off and fly without trouble. But underwater, heaviness doesn't matter as much. Everything gets a boost from buoyancy. What matters more, the authors say, is drag.

To study how drag from tags affects marine animals, NOAA scientist T. Todd Jones and his coauthors put turtles into a wind tunnel. They chose turtles because they're popular—more than 50 published studies per year involve sticking some kind of device to a turtle. Some sea turtle species migrate across entire oceans, so they may carry these devices for hundreds or thousands of miles. And most are endangered.

Instead of propping up live endangered animals inside their wind tunnel, the researchers built fiberglass models. These were casts of 11 types of turtle bodies, minus the front flippers, made from frozen or stuffed carcasses. (The carcasses themselves were too heavy to mount in the wind tunnel.) The researchers also compared a fiberglass cast to a real turtle carcass in water, to make sure the shell materials themselves didn't cause different amounts of drag.

Turtles, of course, don't fly. "Air and water are both fluids," Jones explains; by matching the Reynolds number—a measurement representing turbulence—of the wind to that of water, the scientists could simulate a swimming turtle. Wind speeds of 8 to 20 meters per second corresponded to turtle swimming speeds of 0.5 to 1.3 meters per second.

Attaching seven different kinds of tags to their fake turtles, the researchers saw that most devices increased drag on adult turtles by 5% or less. With a young turtle and a bulky tag, though, it's possible to double the normal drag on the animal. The authors provide charts that other scientists can use to estimate how much drag they're adding to a turtle, based on the animal's size and species as well as the size and shape of their equipment.

It's nearly impossible to tell how tagging equipment affects animals in real life, thanks to a Schrödinger's-turtle paradox: we can't follow the long-term activities of ocean animals that aren't tagged in some way, so we can only compare tagged animals to other tagged animals. However, Jones worries that putting a lot of extra drag—or even a little extra drag—on an animal like a sea turtle could be harmful. These species may burn through every last bit of their energy as they make long-distance migrations, so any extra burden could hurt their odds of surviving and reproducing. (The added brake on their swimming speed might also make them more vulnerable to predators.)

"By following our guidelines, researchers can minimize the drag effects to their study organism," Jones says. This should help keep animals as safe as possible, and keep scientists' results in line with natural conditions for the animals. "However," Jones adds, "sometimes the guidelines will suggest that a certain tag simply should not be used on a particular animal."

Since sea turtles sometimes carry barnacles on their shells, which also add drag, Jones recommends that researchers take the time to pry off a few barnacles while they're gluing on equipment. That way they can make up for some of the extra burden on the turtle, and perhaps alleviate their own guilt about replacing one pest with another.


T. Todd Jones, Kyle S. Van Houtan, Brian L. Bostrom, Peter Ostafichuk, JonMikkelsen, EmreTezcan, Michael Carey, Brittany Imlach, & Jeffrey A. Seminoff (2013). Calculating the ecological impacts of animal-borne instruments on aquatic organisms. Methods in Ecology and Evolution DOI: 10.1111/2041-210X.12109

Images: top, USGS/photo by Kristen Hart; middle, T. Todd Jones.

What Left-Handed Ultimate Fighters Tell Us (or Not) About Evolution

Don't despair, left-handers who have just smeared the ink across your paper yet again. You have a true purpose in life, some scientists say—and it's walloping other people in the head. A flying elbow drop would work too. Researchers recently pored over video of hundreds of UFC fights to test the idea that lefties evolved with an edge in hand-to-hand combat.

Various other animals show a preference for one paw, or one swimming direction, over the other. But humans are notable for almost always preferring the right side. Only about 10 or 12 percent of us are lefties. Is this because there's a cost to being a left-handed human (aside from the ink thing)? Lefties are smaller in stature, and there's some evidence that they don't live as long. If these effects really add up to a raw evolutionary deal, perhaps the reason there are any lefties is that there's some advantage too.

Enter the so-called fighting hypothesis, which says that lefties have persisted at low numbers because they have the element of surprise in a fight.

In order for this theory to make sense, you have to imagine that sometime after our ancestors came down from the trees but before they built weapons, punching each other became very important to their survival. And that despite our squishy outer coverings, valuable dextrous hands, and vulnerable heads, we are a species built for combat. It's a speculative theory. A recent review paper about the fighting hypothesis—which shared an author with the current paper—called evidence for the idea "not particularly strong."

Nevertheless, a group of researchers in the Netherlands chose to explore the theory using mixed martial arts fighters. The UFC "seemed like a very interesting arena to test this hypothesis," says lead author Thomas Pollet, "pun intended." Pollet is a psychologist at VU University Amsterdam. Since the UFC is "a fierce fighting sport hardly constrained by rules," the authors write, it might be a good representation of humans scrapping in an ancestral state.

Pollet studies handedness but didn't have a particular interest in the Ultimate Fighting Championship when he began the study. To get perspective from a fan, I wrote to my friend Ryan, who happens to love watching MMA fighting. He's also a lefty. "A left-handed fighter will lead with their right foot, jab with their right, and cross with their left," Ryan explained. This is all unexpected to an opponent who mainly fights righties. "The speedy jab will come from the opposite side, and the lefty fighter will naturally circle the ring in the opposite direction as well."

Studying recordings of 210 UFC fights, Pollet found that lefties were significantly more common than in the general population. More than 20 percent of the 246 fighters were left-handed. (You can tell by checking their feet; the back leg corresponds to the dominant hand. "UFC fighters only rarely switch between stances within or between fights unless their lead leg is...severely injured," the authors write.)

To look for a left-handed advantage, Pollet analyzed all the fights between a lefty and a righty. The results were an exact tie. A computer simulation in which the fighters' handedness was randomized led to the same conclusion: left-handers had no advantage over righties.

This alone might not disprove the fighting hypothesis. That's because the UFC represents the cream of the lawless-brawling crop. "A fighter must go through a minor league promotion in their home town before making it to the big stage," Ryan told me. On their way to the professional level, left-handed fighters might have an advantage, which would explain why there are so many of them in the UFC. But once they become more common—and face more opponents who are experienced at fighting lefties—their edge might disappear.

"I think it is a very attractive hypothesis," Pollet says. The advantage of being left-handed in a fight may depend on how many other lefties are around, but "testing frequency dependence can be hard," he says. He's hoping to compare results in the UFC to other competitions that include more amateurs.

Currently, Pollet and his colleagues are working on a meta-analysis of lefties in different sports. In tennis, for example, being left-handed can give players a boost. (My friend Ryan, who just happens to also play tennis, said that being a lefty gave him "a great advantage growing up." A lefty cross-court forehand shot, he explained, forces your right-handed opponent to return the ball with a weaker backhand.)

In addition to the UFC, left-handedness is especially common among badminton players, cricketers, and recent U.S. presidents. Maybe lefties can look to those areas to find their evolutionary reason for being. If they still feel existential angst, they can always go out and punch someone.


Image: by Krajten (via Wikimedia Commons)

Thomas V. Pollet, Gert Stulp, & Ton G.G. Groothuis (2013). Born to win? Testing the fighting hypothesis in realistic fights: left-handedness in the Ultimate Fighting Championship. Animal Behaviour DOI: 10.1016/j.anbehav.2013.07.026

Thanks to Ryan Sponseller for his thoughtful comments on handedness and punching dudes.

Beetles Show There Is Such Thing as a Free Lunch, and It's a Weapon Attached to Your Face

If the rhinoceros beetle were the size of an actual rhinoceros, its horn could be 16 feet long. Male beetles grow this gargantuan face-fork so they can win mates (why else?). And even though evolutionary science would predict that the beetle pays a price for this appendage, it seems to come absolutely free.

Males of many animal species wear showy accessories: antlers on deer, long tails on birds. Growing one of these accessories often comes at a cost. For example, energy spent growing one large body part may leave another body part smaller, as seems to be the case with the dung beetle's horns. Or the showy feature may make the animal more vulnerable, as in the Bahamas mosquitofish, which grows a large sperm-delivery organ to impress females but then can't swim away as quickly when chased by predators. Females benefit from being choosy, because males that can afford to spend resources on a fancy headpiece or tail demonstrate that they're hardy or have good genes.

Erin McCullough, a PhD student at the University of Montana, Missoula, and her advisor, Douglas Emlen, have been putting rhinoceros beetles through the wringer to try and find the cost they pay for their giant horns. Individual males grow horns of widely varying sizes. In the Japanese rhinoceros beetle, Trypoxylus dichotomus, horns range from a stubby 7 millimeters to a towering 32. In other species, the largest horns are 10 times the length of the smallest ones.

In a previous paper, the researchers showed that larger horns—somehow—don't hurt the rhinoceros beetle's ability to fly. Now, they measured the horns of T. dichotomus beetles and compared their size to the insects' legs, wings, eyes, and genitalia. They also tested the strength of the beetles' immune systems. And by marking beetles with paint, releasing them outdoors, and recapturing them later from the same area, the researchers assessed whether larger horns make a beetle more likely to die.

The result was a big goose egg. Nothing. If you're a rhinoceros beetle, there is apparently no trade-off to growing the biggest horn you can.

So why aren't all horns huge? Males with larger bodies are able to grow disproportionately longer horns than smaller beetles; Emlen found in an earlier study that this is tied to the beetles' insulin levels. "Males that have poor nutrition and therefore have low levels of circulating insulin simply can’t produce big horns," McCullough explains.

Still, if big horns are so great, evolution might favor males who can use their good nutrition to grow ever-larger appendages. Why is there any limit on the size of the horn? "I think the primary reason...is because they are weapons that are continuously tested in combat," McCullough says. Male rhinoceros beetles use their horns to fight each other for the best territory on tree trunks and branches. Grappling over sap-rich sites, they wield their horns like pitchforks to pry rivals loose. "So it doesn’t benefit a male at all to have a horn that’s so large that he can’t use it properly," she says.

McCullough is currently testing that idea by measuring the force needed to pry a male beetle from a tree and comparing it to the force needed to snap the beetle's horn. She thinks longer horns are at more risk of breaking, and that this may be what limits their size.

The reason rhinoceros beetles escape paying for their horns might be that they're functional, and not merely a decoration. When birds pay a price for a showy tail, it ensures that only the genetically strongest birds can give the best display to females. If unhealthy birds could cheat and grow fancy tails at no cost, females would no longer benefit from favoring good tails—so they'd stop paying attention at all, and males would stop bothering. But because there's a cost, the system works. In the case of the rhinoceros beetle, McCullough and Emlen believe cheaters are weeded out because they can't fight with their oversize horns. This means the flashy gear comes for free—as long as the beetle knows how to use it.


Erin L. McCullough, & Douglas J. Emlen (2013). Evaluating the costs of a sexually selected weapon: big horns at a small price. Animal Behaviour DOI: 10.1016/j.anbehav.2013.08.017

Image: McCullough & Emlen.

Snoozing on the Weekend Won't Undo Workweek Sleep Loss

Does your workweek schedule dig you into an ever-deepening hole of sleep deprivation? Do you sleep in on the weekends to try to boost yourself back out? You're in good company. But even if you feel recovered by the following week, your brainpower might be suffering.

In a survey by the National Sleep Foundation, 40 percent of respondents said they try to "catch up" on sleep during the weekend. Pennsylvania State University professor and physician Alexandros Vgontzas, along with a group of colleagues, recruited 30 subjects to study how well this catching up really works. The subjects were healthy men and women between 18 and 34 (who didn't mind the prospect of sleeping with a catheter in their arm).

For two weeks before the study, researchers made sure subjects got 7.5 to 8 hours of sleep every night. Then the subjects came into the sleep lab. The experiment began with three "baseline" nights of 8 hours' sleep. For the next five nights, their sleep was restricted to just 6 hours, mimicking a full workweek of uncomfortably early rising. Then subjects had two "recovery" nights where they were left sleeping for 10 hours.

During most days of the experiment, subjects were allowed to go home and follow their normal routine—though monitors on their wrists made sure they followed strict no-napping instructions. At night, they returned to the lab. And after each phase of the experiment, subjects spent a full 24 hours undergoing tests: researchers tracked the levels of hormones circulating in their blood and gave them cognitive tests. They also asked subjects to rate how sleepy they felt. To measure their actual sleepiness, researchers had subjects lie down to nap, recorded how long it took them to conk out, and woke them up again—six times a day.

Predictably, subjects were sleepier during their week of sleep deprivation. It took them less time to fall asleep during the day, and the easiest time for them to nap was 9:00 in the morning (as opposed to 3:00 in the afternoon during the baseline period). After their two recovery days, subjects' sleepiness returned to normal.

One hormone the scientists monitored was IL-6, a marker of inflammation in the body. They found that IL-6 increased when subjects lost sleep. This fits with what earlier studies have found, and suggests one way sleep deprivation is bad for your health. IL-6 levels dropped back to normal after the two nights of recovery sleep.

The only measurement that didn't go back to normal was performance on a test called the psychomotor vigilance task (PVT). Subjects did this test every two hours during their lab days. In it, they watched a screen for ten minutes and pressed a button every time a certain number appeared. It's a test that measures a person's ability to sustain attention; astronauts on the International Space Station do a similar test on themselves to check for fatigue.

Subjects in the sleep study did worse on the PVT after their sleep-deprived week, and continued to do poorly even after two nights of catch-up sleep. Vgontzas says he doesn't know why this is. But apparently some function in people's brains hadn't recovered fully by the end of the experiment, even though they felt well rested.

It's worth noting that because there was a 24-hour testing period after each stage of the experiment, subjects actually had a sixth night of poor sleep before their "weekend." And some champion snooze-button users can sleep well past 10 hours on their real makeup days. Still, Vgontzas's findings suggest our brains are slow to catch up after losing sleep—specifically, our ability to pay attention suffers—and we might not know when we're mentally fatigued.

Vgontzas also doesn't know what the cumulative effect might be of living this way every week. On average, he writes, we need seven hours of sleep a night. (Though if you really can't sleep any later, a nap during the day will also help you recover.)


Image: by Phae (via Flickr)

Pejovic S, Basta M, Vgontzas AN, Kritikou I, Shaffer ML, Tsaoussoglou M, Stiffler D, Stefanakis Z, Bixler EO, & Chrousos GP (2013). Effects of recovery sleep after one work week of mild sleep restriction on interleukin-6 and cortisol secretion and daytime sleepiness and performance. American journal of physiology. Endocrinology and metabolism, 305 (7) PMID: 23941878