Field of Science


12 Days of Inkfish, Day 7: Yearbook

With the year drawing to a close, Inkfish's class officers have chosen superlatives to bestow on the posts of 2012. Please note that a prom king and prom queen were not elected this year because everyone was too busy cheering on the mathletes. (Hey, wildfires in the Cretaceous won Most Popular. Anything's possible.)

Most Popular

Cutest Couple

Class Clown

Worst Hygiene

Most Talkative

Most Athletic

Class Goth

Most Likely to Attend Culinary School*
*This post was also nominated for Most Disgusting Use of an Innocent French-Toast Photo.

Most Likely to Join AA

Best Mustache 

Thanks for taking a minute to reflect on 2012 with me; I'll see you next year. Have a great summer!

Image credits can be found at their respective posts.

12 Days of Inkfish, Day 6: Zion Canyon

Stories about earth science have all the transformations and power struggles of a fairy tale. When I asked my friend Tyler Auer—a photography blogger who studied geoscience in college—to tell me the story behind a favorite photo, he sent me a tale that’s part Princess and the Pea and part Jurassic Park.

Tyler took this picture at Zion Canyon, one of the many national park areas (including the Grand Canyon) within the 130,000-square-mile formation known as the Colorado Plateau.

“Around the time the dinosaurs roamed the western US, the Colorado plateau was a giant sea of sand dunes,” Tyler says. Over millions of years, these sand dunes kept forming on top of one another and compressing into layered sandstone. You can see the outlines of the ancient dunes, like so many stacked mattresses, in the striations of the canyon walls.

While the sand dunes were turning to rock, they were also being pushed upward by tectonic activity. Cracks formed in the ground like the crust of a bread loaf in the oven. Zion Canyon began as one of these cracks. But “sandstone is really soft, as far as rocks go,” Tyler says, “and running water carves through it quickly.” Rainwater and the flow of the Virgin River gradually deepened this split into a half-mile chasm with almost vertical walls.

Since the Colorado Plateau may be the thickest sandstone layer that’s ever formed, it's provided nature with a deep toolkit. “The Colorado Plateau is magnificent example of the slow but beautiful work nature can do,” Tyler says. You can find more fairy-tale pictures at his blog.

Image: Virgin River Narrows north of Zion Canyon, by Tyler Auer

12 Days of Inkfish, Day 5: Running on Water

Human courtship rituals—if you believe television commercials, anyway—are lame. The guy who kneels down right at the jewelry store counter ("It fits perfectly!" "Well honey, that's because I already had it sized") has nothing on birds who walk on water for each other.

Grebes are diving waterbirds that live in the Americas and Eurasia. To pair off, they follow an elaborate courtship choreography that includes trading bits of food and mimicking each other's motions. In the ritual's conclusion, both birds suddenly haul their ungainly bodies out of the water and run together on its surface. The grace of the birds and the physics of the maneuver both seem impossible.

You can see a pair of Clark's grebes do their courtship dance in this incredible video from the BBC. Jewelry companies, take note: there's no prelude to romance quite like swallowing a live fish.

Image: screen grab from BBC Life: Birds: Partners for Life

12 Days of Inkfish, Day 4: Help Desk

When you use website analytics, you quickly learn that there are a lot of people out there Googling things like "how do i make robot" and "which is best medicine for make baby." This year I've seen many visitors whose search queries were probably not answered here. To make things up to them, I'll try to address a few of those questions now.

orangutan stop following me
Unless you live in Borneo or Sumatra and spend a lot of time in rainforest trees, it's very unlikely that you're being followed by an orangutan. Are you sure it isn't a very hairy human or a large orange dog? If an orangutan is, in fact, following you, don't worry—they mostly eat plants.

can you use ab toning belt on butt for bigger muscles
Ab toning belts will not make your muscles stronger (they only stimulate the surface of the muscle) or more toned (because the contractions are involuntary). But if you're really attached to the idea, don't bother strapping the belt around your rear: they sell toning shorts too.

what pills can make a man's hair fall out in clumps
I don't know the answer to that but it sounds like you're working on a super hilarious prank.

toilet training pigeon
Here's a website with some advice on potty-training pet birds. Consistency is key! But if I had a pigeon I'd skip the toilet training and teach it to carry messages, or to find its home from hundreds of miles away. Or to take pictures, like those cool pigeons in World War I.

is science harmful or useful
Did you not just see that pigeon with a camera strapped its chest?

giant barbies on the loose
Please send a picture so I can better assess the problem. Maybe you and the person with the orangutan problem should coordinate.

that story about the monkeys in the room
Your faith in organic search is touching. I don't know what you're looking for, but here's a story about rhesus macaques raised by water bottles instead of mothers.

if you swap brains will you still have the knowledge inside?
Even if this question is only research for a science-fiction story, I really think you should reconsider.

unnecessary otter

sex robot sperm go?
Since you clearly know search terms don't have to be in the form of a coherent sentence, I'm confused about why you think they still need a question mark at the end. On the off-chance you're wondering what the similarities are between a sperm cell and a Roomba, here are some.

why is sperm brown
Wow, please see a doctor. Why are all the sperm people coming here?

i have to pee
No one is stopping you. 

what company makes placebo
Okay, I quit.

Images: Help desk by Aryc Ogre; war pigeon via Wikimedia Commons 

12 Days of Inkfish, Day 3: Reverse Sun

"Astronomy! People go crazy studying that!" a Christmas tree farmer said this week after asking my younger sister her college major. He made a head-exploding gesture to illustrate his point.

That farmer might have been distressed by this image. Despite its similarity to sperm tackling an egg, it's really a color-inverted picture of our sun. The background is a field of stars, also with its colors reversed.

Turning the colors around lets us see features on the sun's surface we might not otherwise. The little bumps and crinkles are called granules; they're where hot gas is rising to the outside of the sun before cooling and sinking again. According to a textbook of my sister's, these bumps are "typically the size of Texas."

The image comes from NASA's Astronomy Picture of the Day, which provides new head-explosions every 24 hours.

Image: Jim Lafferty

12 Days of Inkfish, Day 2: Upside-Down Jelly

Cassiopea jellyfish spend much of their adult lives lying on their backs. Or maybe their heads. However you look at it, they're upside-down: they rest in warm, shallow waters, holding their branching arms up toward the sun. Inside those tentacles are single-celled algae, which photosynthesize and provide food for their jelly farmers.

Cassiopeia, the jellyfish's differently spelled namesake, was a queen in Greek mythology. After bragging that she was even more beautiful than sea nymphs called the Nereiads, the queen was punished by having her constellation placed where it sometimes appears upside-down as it rotates in the sky.

The jellyfish are passive but have a mild sting. Some crabs hoist Cassiopea jellyfish onto their backs for self-protection, carrying them around gardens and all.

Image: Cassiopea jellyfish at Shedd Aquarium, taken by me. If you like seeing bizarre animals up close (or adults with their faces pressed up to glass like kids), go see this exhibit.

12 Days of Inkfish, Day 1: Gifts

Consider this a big, many-tentacled squeeze from me to you.

This year, I've expanded into new habitats, learned new tricks (like driving the Shambulance), and seen lots of new readers swimming by. I'm grateful to every person who visits and shares these pages. You've given me a reason to learn about wine-making wasps and anti-placebos, to taste no-calorie noodles and verbally abuse sheep. Say hello in the comments!

For each of the 12 days of Christmas I'll be leaving a little something here to unwrap. The first is a video of an octopus receiving a live crab in a jar. After menacing the crustacean briefly, it unscrews the jar's lid and squeezes its whole body inside to devour its prey. Talk about a stocking stuffer.

Video from CBCtv.

Fossil Scan Reveals Ghost of Lizard Past

Peering into the past life of this fossil took an x-ray scanner powered by a particle accelerator. What scientists saw there was mysterious: an ancient lizard had left behind its skin and teeth, but none of its bones. To tell the ghost's tale, they relied on some very modern equipment.

At Stanford University, an accelerator called a synchrotron sends electrons zipping around a track fast enough that x-rays spin off of them. These x-rays are collected into an extremely bright x-ray beam that scientists can use for various projects. One application, x-ray fluorescence, lets researchers map the actual chemical elements inside on object.

Other methods of analyzing an item's chemical makeup require scientists to focus on tiny slices, destroy their samples entirely, or creep along at a rate of one square centimeter a day. But the setup at Stanford lets scientists look quickly and thoroughly at larger objects while keeping them in one piece. The synchrotron has previously been used to reveal writings of Archimedes that were scraped away and painted over, and to deduce the pattern on the feathers of the 120-million-year-old Confuciusornis.

University of Manchester paleobiologist Phillip Manning and his colleagues, who had worked on scanning Confuciusornis and other fossils, now turned the synchrotron's powerful x-ray beam onto an unusual fossil. The 50-million-year-old lizard specimen comes from Colorado. What's unusual is that the animal's skin is beautifully preserved, right down to the scales—but the skeleton is gone.

Scanning the fossil for sulfur (in the photo above) or copper produced ghostly silhouettes of the lizard's whole body, since these elements are naturally present in trace amounts throughout an organism. Tuning their scans for phosphorous brought a surprise: dots popped out of the lizard's ghostly head in the shape of a jaw.

In the image above, green is a map of sulfur in the head and neck (check out the scales!). Phosphorous and magnesium are overlaid in red and blue. The authors write that this chemistry is "typical for biomineralized structures." A close look revealed two overlapping bites: a full set of lizard teeth.

Before the synchrotron scanning, researchers thought the unusual Colorado fossil was a 50-million-year-old molted lizard skin. But even animals that shed their skin don't tend to leave behind their entire jaws when they do so. This animal died in one piece.

Although bones and teeth have similar ingredients, the authors write that the structure of teeth makes them more resistant to dissolving. But how did the delicate skin stay intact? "If the acidity of the ground waters are high, bone would be vulnerable," Manning says. "However, high acidity is often helpful in 'tanning' skin to preserve [it]. Think bog bodies from northern Europe."

As researchers continue to peer into the past with the synchrotron, Manning is narrating their progress at his blog. He doesn't anticipate running out of subjects. "We have a few million life forms to wade through," he says. In other words, there are plenty of ghosts of fossils yet to come.

Edwards, N., Wogelius, R., Bergmann, U., Larson, P., Sellers, W., & Manning, P. (2012). Mapping prehistoric ghosts in the synchrotron Applied Physics A DOI: 10.1007/s00339-012-7484-3

Images: Edwards et al.

Are You Healthy Enough to Be a Space Tourist?

Space travel for regular folks is almost here. But before jumping on board the nearest spacecraft, amateur astronauts and their doctors might want to consider the health risks. Although standard air travel is more boring than spaceflight, it's also less likely to shrink your bones or deform your eyeballs.

"Practically only the healthiest people have flown in space so far," says Marlene Grenon, a vascular surgeon at UCSF who researches the effects of microgravity on the body. Government astronauts go through extensive medical testing and training. But even these extra-fit fliers have suffered ailments ranging from cardiac dysrhythmia to good old-fashioned vomiting. What's in store for the rest of us?

Grenon is the lead author of a paper in BMJ asking that question. The researchers say that doctors will have plenty to consider before sending their patients to boldly go where no civilian has gone before.

"Space motion sickness would be expected to be the most common" medical problem, Grenon says, "particularly for short-duration flights." If your inner ear is easily confused by sitting still in a moving vehicle, just imagine what happens when that vehicle has no up or down.* NASA's parabolic flights—trips on aircraft that fly in steep up-and-down waves, simulating weightlessness for astronauts in training and scientists researching low gravity—have earned the nickname "vomit comets" for a reason.

Life without gravity is hard on the bones and muscles as well as the barf reflex. NASA astronauts onboard the space station exercise for two hours every day to counteract bone loss, muscle atrophy, and a decrease in cardiovascular fitness. Grenon says she doesn't yet know how weightlessness might act on people who are less fit to begin with, or overweight.

Exercise may prevent muscle atrophy but it doesn't do much for squished eyeballs. A study last year found that after a six-month space mission, astronauts were likely to have "flattened globes" and other eye problems. The shifting of fluids inside the head, free to bounce off the walls just like the astronauts themselves, might be to blame. Even after shorter trips, many astronauts reported worsened eyesight.

The authors of the new paper name several medical conditions that might worsen in microgravity. For people with diseases of the blood vessels, fluids drifting around might be dangerous. Aneurysms could rupture during takeoff. Bone loss in space could be especially bad for people who already have osteoporosis. Acid reflux could worsen when the esophagus no longer knows which way is up. And don't forget radiation exposure.

But the most ordinary complaint that might ground you is an infection. Grenon writes that even people with simple ear or skin infections should consider postponing trips to space.

That's because the immune system changes during spaceflight, Grenon says. Although these changes are not well understood, they "could place the spaceflight participants at higher risk of infection." Additionally, she says, "Some research has also hinted [at] the fact that bacteria grow stronger in microgravity." And radiation might make people more susceptible to infection—or make bacteria mutate more quickly. Overall, the changes in space favor bacteria over your immune system. These risks would be greater on longer flights.

Still want to fly? Virgin Galactic is accepting reservations. If you're willing to put down $200,000 up front, you can still get a spot on their first round of flights. For a cool million you can reserve a private trip for yourself and five friends—that's a buy-five-spaceflights, get-one-free deal. Make sure you pack enough barf bags.

Grenon, S., Saary, J., Gray, G., Vanderploeg, J., & Hughes-Fulford, M. (2012). Can I take a space flight? Considerations for doctors BMJ, 345 (dec13 8) DOI: 10.1136/bmj.e8124

Image: U.S. Air Force

*For an exceedingly thorough discussion of space barfing, as well as other bodily functions performed in microgravity, I recommend Mary Roach's book Packing for Mars.

Malaria Makes Its Victims More Tempting to Mosquitos

Think mosquitos have a special fondness for you? Do they choose to target you over adjacent humans? No matter how badly you have it, things might be worse if you were infected with malaria. New research in birds shows that malaria parasites somehow make their victims more attractive to mosquitos. After all, the parasite needs a lift to its next destination—so it forces its sick host to flag down a ride.

Malaria, one of the top killers worldwide among infectious diseases, isn't caused by a virus or a bacterium. The culprit is a one-celled protozoan, called Plasmodium, that comes in a couple hundred disease-causing flavors. Plasmodium falciparum is the species that causes most malaria deaths in humans.

Various other Plasmodium species infect birds, reptiles, and mammals ranging from apes to anteaters. Whichever animal it prefers, the parasite needs to travel to new hosts via the belly of a mosquito. If possible, Plasmodium shouldn't just rely on chance—it should encourage mosquitos to bite its host.

In a 2005 study, researchers found hints that mosquitos are more attracted to the smell of a malarial child than a healthy one. (This was only true once the parasite had reached the right life-cycle stage for spreading to other people.) Giving malaria to kids is hard to justify ethically, though, even if you then treat them with antimalarials as those researchers did.

To pursue the question without leaving behind a trail of sick children, researchers in France turned to birds. Author Stéphane Cornet, of the Centre d'Ecologie Fonctionnelle et Evolutive, says the avian malaria parasite the team used infects more than 30 bird species around the world. For their experiments, they used canaries.

Mosquitos could prefer sick animals simply because they're easy targets. "Infection often renders hosts lethargic, as we are when we feel sick," Cornet says, "so that they are less able to defend themsleves against [mosquito] attacks." But he and his coauthors were more interested in whether malaria changes the particular bouquet of an animal to tempt to passing mosquitos. So they placed all their canaries inside PVC tubes with only their legs sticking out. This way, the birds' behavior and appearance wouldn't matter.

Fifty canaries were divided into pairs. Then the researchers released 70 hungry female mosquitos into a cage with each pair of birds (or, from the mosquitos' perspective, a cage holding four bird legs). After the mosquitos had feasted, the authors checked the DNA of the blood in their bellies to find out which bird each mosquito had chosen. Every mosquito choice test was repeated three times.

After testing mosquitos on healthy birds, the researchers infected one bird in each pair with avian malaria and repeated the tests 10-13 days later, when the birds were sickest. Two weeks after that, they tested the mosquitos and birds a final time. By then, 9 birds had died. But the surviving infected birds had entered the "chronic" stage of infection, when the parasite lies low and the victim isn't as sick.

Mosquitos weren't any more interested in acutely ill birds than in healthy birds, the researchers found. This might have been because the malaria had driven down their red blood cell counts, making their blood less delicious to mosquitos. But once the canaries entered the chronic stage of malaria, mosquitos clearly preferred to feed on the infected birds. The authors report their findings in Ecology Letters.

Cornet believes malarial birds give off some signal to attract mosquitos, such as extra carbon dioxide or a specific odor. What exactly that signal is, and how the Plasmodium parasite manipulates its host into sending the signal, remains a mystery.

A canary is of course not a person, and their malaria parasites are different from ours as well. But there are similarities in how the two parasites act on their hosts, Cornet says. Humans, like birds, might give off some mosquito-enticing perfume when infected with malaria. Finding this perfume could help prevent malaria transmission in the future. And even before that happens, Cornet says, it's useful for people who model the spread of malaria to know that mosquitos aren't choosing their victims randomly.

If you're still feeling resentful toward mosquitos, it may help to know that the malaria "perfume" is really a trap. Mosquitos that carry Plasmodium parasites are about a third less fertile than they would be otherwise, another study this year found. Drinking from infected hosts is bad for mosquitos just like it's bad for the next animal they bite. But, like us, they're helpless to Plasmodium's wiles.

Cornet, S., Nicot, A., Rivero, A., & Gandon, S. (2012). Malaria infection increases bird attractiveness to uninfected mosquitoes Ecology Letters DOI: 10.1111/ele.12041

Image: Travis S. (Flickr)

Ancient Insect Carried Built-In Trash Basket for Camouflage

Covering yourself with garbage is a great way to look less delicious to predators. More than a hundred million years ago, one insect species took this strategy to the extreme by growing a kind of giant trash can on its back. Scientists could identify the new species thanks to a remarkable specimen that was preserved—along with an informative topping of trash—in amber.

The insect that kindly died in a blob of tree resin in early-Cretaceous Spain was a young green lacewing. Modern-day green lacewings are predatory insects common in North American and Europe. Before they develop their lacy adult wings, the larvae of some species protect themselves by carrying trash around. They collect plant material, insect carcasses, and other debris in their jaws, then twist their heads around to tangle the material into short appendages growing out of their backs. The trash camouflages them and provides a physical, untasty shield when predators (which can include ants, wasps, and cannibalistic green lacewings) attack.

But the Cretaceous lacewing was so wildly different from its modern-day relatives that scientists named it Hallucinochrysa—that is, an insect bizarre enough to seem like a hallucination. (For its second name they chose diogenesi in honor of Diogenes syndrome, a trash-hoarding disorder in humans. The disorder, in turn, is named after a Greek philosopher who lived in a tub.)

University of Kansas entomologist Michael Engel, one of the authors of the new paper in PNAS, describes the ancient lacewing's trash-carrying apparatus as "dramatic and unique." Unlike the short appendages on modern green lacewings, the old insects grew a thicket of extremely long, hairy tubes from their backs (illustrated above).

Coauthor Ricardo Pérez-de la Fuente, of the University of Barcelona, points out another unusual feature of the trash basket: the tiny hairs growing out of the tubes have "trumpet-shaped endings," which he says would have helped anchor the trash in the basket. Once the refuse was in place, it stayed there.

Almost as exciting as the hallucination-worthy insect was the collection of trash preserved with it. "What attracted our attention since the very beginning was the high density and intricacy of the trash packet," Pérez-de la Fuerte says. Peering into the amber with a microscope, the researchers identified the thread-like plant parts trapped on the insect's back as bits of ferns.

The plants seem to match a tropical group of ferns that, these days, move into areas swept clean by wildfire or lava. Since ancient wildfires also encouraged amber to form, and this particular sample was part of an abundant amber cache, it seems likely that the area had experienced fire. At least one trash-toting insect had filled its basket with bits of the ferns that sprouted afterward. Then this insect carried its garbage collection up into a tree and died.

Since the ferns lived on the forest floor, their remains would have been "extremely unlikely to be found otherwise," says Pérez-de la Fuerta. The day this little trash hoarder walked into a sticky tree was a bad one for the insect, but a very lucky one for scientists.

Ricardo Pérez-de la Fuente, Xavier Delclòs, Enrique Peñalver, Mariela Speranza, Jacek Wierzchos, Carmen Ascaso, & Michael S. Engel (2012). Early evolution and ecology of camouflage in insects PNAS : 10.1073/pnas.1213775110

Image: J. A. Peñas

Cold and Hungry? Scientists Suggest Remembering Soup

Regrettably, and despite what the Breatharians will tell you, a person can't live on a diet of air. But you can keep hunger pangs at bay, scientists say, simply with the power of memory. And feelings of nostalgia can help you withstand cold, according to another group of scientists. Now that winter is settling in, it might be a good time for all of us to start collecting some really good soup experiences.

Researchers studied the effect of nostalgia on body temperature in a series of experiments reported in the journal Emotion. People may describe their fond thoughts of the past as "warm feelings," but do they really mean it?

In one experiment, 64 subjects individually sat in a room kept at a cool 16 degrees C (60 F). They were asked to recall either a memory that made them nostalgic or an "ordinary autobiographical event." After taking some time to reflect on the memory and record their feelings, subjects estimated the temperature of the room. The ordinary-memory people guessed about 17 C (63 F). But the nostalgic ones put the temperature higher, at around 20 C (a comfortable 68 F).

Another group of 80 volunteers reflected on a nostalgic or non-nostalgic memory, like the earlier group had. Afterward, they had to plunge one hand into a bowl of ice-cold water and hold it there for as long as they could. The non-nostalgic subjects lasted about 20 seconds before yanking their hands out of the bowl. Those fortified by warm, nostalgic memories, though, stuck it out for an average of 26 seconds.

A separate study, published this week in PLOS ONE, looked at how memory affects hunger. Patients with severe memory problems, the authors note, sometimes eat one full meal right after another—without recalling what they've eaten, they apparently don't feel full. For people with intact memories, does hunger also depend on our memory of our last meal?

To find out, researchers at the University of Bristol relied on a trick soup bowl. A hidden pump in the bowl's base, connected to a tube under the table, let scientists sneakily refill or drain the bowl while subjects were eating (surely this is the plot of a Greek myth I'm forgetting).

Researchers gave 100 subjects a bowl of "creamed tomato" soup that initially held either 500 ml (about 2 cups) or 300 ml (1 1/4 cups). Half the subjects were allowed to eat their soup with no funny business. A quarter of them saw a bowl holding the larger amount of soup but only ate the smaller amount as their bowls were secretly drained. And the final group saw a small bowl of soup but ate a larger portion as it refilled.

Over the next three hours, subjects rated how hungry they felt. By the end, people who had seen a small portion of soup felt significantly hungrier than those who had seen a large portion—regardless of the amount they'd actually eaten.

This suggests, the authors write, that appetite is closely tied to our memory of what we've eaten recently. We take visual hints from our food about how full it will make us feel, and those hints can override the information coming from our stomachs.

If you don't have a magic soup bowl, you might still be able to use your memory to your advantage by paying attention to what you eat. Previous research has shown that watching TV, or otherwise distracting ourselves during meals, can make us hungrier later on. Taking in all the visual information from our plates, so we remember it later, can keep us feeling fuller. And, of course, recalling fond memories might make us warmer. Maybe all that time Eliza Doolittle spent standing on the street and singing about "warm face, warm 'ands, warm feet!" would have been better spent looking to the past.

Zhou, X., Wildschut, T., Sedikides, C., Chen, X., & Vingerhoets, A. (2012). Heartwarming memories: Nostalgia maintains physiological comfort. Emotion, 12 (4), 678-684 DOI: 10.1037/a0027236

Brunstrom, J., Burn, J., Sell, N., Collingwood, J., Rogers, P., Wilkinson, L., Hinton, E., Maynard, O., & Ferriday, D. (2012). Episodic Memory and Appetite Regulation in Humans PLoS ONE, 7 (12) DOI: 10.1371/journal.pone.0050707

Image: Maria Pontikis (Flickr)

Fishing Yanks the Best Parents from the (Gene) Pool

A fishing rod and reel aren't just gear for human recreation: they're the tools of evolution. The difference between fish we pull out of lakes or commercial fisheries by their lips and those we leave behind can drive change in entire fish populations. And that change may be for the worse. In at least some species, the fittest fish are the ones that end up on our hooks.

The largemouth bass (Micropterus salmoides) lives all over the United States and is a popular target of recreational anglers. You wouldn't guess it from the bug eyes and mailbox mouth, but M. salmoides males are also doting dads. For several days after the female lays her eggs and before they hatch, the male stays close to the nest. He fans the eggs with his tail and chases off any other creatures who come looking for a snack.

The more aggressively a male largemouth bass attacks intruders near his nest, the more of his offspring are likely to survive. But when fending off threats, a bass doesn't necessarily notice the difference between a hungry fish and a dangling lure. So the fish that guard their nests most aggressively might also be the most likely to bite into a fishhook.

David Sutter, a PhD student at the University of Illinois at Urbana-Champaign, and other researchers used specially bred largemouth bass in artificial ponds to investigate this question. Their fish had been bred into two lines: one that's especially likely to attack a fishhook, and one that's especially unlikely.

(Vulnerability to being caught on a rod and line is heritable, Sutter explains—a kind of personality trait for fish. Largemouth bass were first bred this way starting in the late 1970s. Researchers kept the bass in a reservoir where any fish that got caught were marked and rereleased. Eventually researchers drained the reservoir, revealing some fish with multiple marks and others that had never been caught. These extremes were separated into new ponds where the experiment was repeated. After a few generations of this, the researchers had created one line of fish that was consistently catchable and a second line that was consistently hard to catch.)

Sutter and his colleagues put the two kinds of male bigmouth bass together in a pond, along with ordinary females. Once the fish had spawned, snorkelers visited their nests to count their eggs. By spying on the fish remotely, researchers could observe how attentive the fish dads were to their nests—and how aggressive they were to "intruders," which in this case were hookless fishing lures.

The fish bred for catchability, as expected, attacked the fishing lures more often than other fish. In addition to chasing these imaginary predators away from their eggs, they also spent more time hanging out near the nest and fanning their eggs with their tails. By comparison, the fish bred to ignore fishhooks spent more time away from the nest and didn't bother chasing away intruding lures. Overall, as the authors report in PNAS, the easiest-to-catch largemouth bass are also the best dads.

Hooking one of these fish from a body of water obviously removes him—and his good-dad DNA—from that population's gene pool. It also dooms any eggs he was guarding, which carry those same genes, to become food for roving predators.

There's another way fishing fouls up the next generation of fish. The researchers found that females spent more of their eggs on aggressive males, especially large ones. Apparently the female fish can tell which males will guard a nest well. When these sexy bass are removed from a pond, they leave behind more eggs (and more potential young) than a smaller and less aggressive male would.

All this means that humans can drive the evolution of a whole fish population. Thanks to our fishing lines, male largemouth bass (or species with similar behaviors) can become less aggressive, less capable as parents, and less attractive to females. And, of course, less catchable by us. The authors suspect these changes are already happening in popular angling spots, though it hasn't been studied yet.

Sutter says fisheries might be able to prevent the problem by leaving largemouth bass alone during their spawning season. "It would probably be best to allow fish to successfully reproduce and minimize disturbances," he says—by disturbances he means fishhooks—"especially in areas where fish only have limited opportunities to reproduce." Otherwise, the only fish that are left alive may be the deadbeats.

David A. H. Sutter, Cory D. Suski, David P. Philipp, Thomas Klefoth, David H. Wahl, Petra Kersten, Steven J. Cooke, & Robert Arlinghaus (2012). Recreational fishing selectively captures individuals with the highest fitness potential PNAS : 10.1073/pnas.1212536109

Image: (Not a largemouth bass) by Blake Facey (Flickr)