Be Fear Free

(This post first appeared in April 2011. See you all next year!)

If you have a fear of heights, called acrophobia, you probably consider activities such as standing on a glass ledge 103 stories high to be stressful. But a scientist in Switzerland says that cortisol, the stress hormone, can actually help banish your fear.

A team of researchers led by Dominique de Quervain at the University of Basel recruited 40 patients with serious acrophobia. All the patients received a series of virtual reality sessions, in which they traveled across virtual bridges and stood on virtual platforms, to treat their phobia. 

This is a standard and effective treatment called exposure therapy. It assumes that the patient's phobia is a "conditioned response." Just like good old Pavlov's drooly dogs, a person reacts automatically to a specific stimulus (say, being up high) with a specific response (say, panic). But if you repeatedly expose patients to the stimulus in a safe environment, and help them tone down their fear reaction, they learn a new association. If Pavlov had started giving his dogs empty bowls after ringing his bell, they would have eventually stopped drooling.

The patients in the study responded well to the virtual-reality treatments. Their acrophobia was reduced,  according to both questionnaires and skin-conductance measurements. (Your skin gets sweaty when you're worked up; this is how lie detectors work.) 

But there was another factor in the study: half the patients, before each of their treatment sessions, had been given a dose of cortisol. The other half had taken a placebo. The patients who received cortisol had a greater reduction in their phobia than the placebo patients, both a few days after treatment and a whole month later.

It seems like a counterintuitive result. Why would stress make you less afraid? The answer may have to do with memory. Cortisol can impair your ability to retrieve memories, especially emotionally powerful ones. This could include your memories of previous panic attacks--or a memory of a traumatic event that inspired your fear in the first place. Additionally, cortisol helps you to store new memories. In general, the stress hormone tells your body and brain that what's happening right now is vitally important. In exposure therapy, cortisol may give extra weight to new memories of experiencing a stimulus in a safe setting, while simultaneously damping down fearful memories.

The paper's authors are also studying the use of cortisol in treating social phobia, a condition that causes some people to avoid all social interaction. For the rest of us, the results may not be as life-changing. But they tell us that it's OK to feel stressed when we face our fears. If this inspires you to go up the Sears/Willis Tower, just make sure to bring a camera so you can prove you did it.

de Quervain, D., Bentz, D., Michael, T., Bolt, O., Wiederhold, B., Margraf, J., & Wilhelm, F. (2011). From the Cover: Glucocorticoids enhance extinction-based psychotherapy Proceedings of the National Academy of Sciences, 108 (16), 6621-6625 DOI: 10.1073/pnas.1018214108 

Photo: by me.

Eternal Sunshine of the Spotless Slug

This post first appeared in May 2011. Yes, I'm on vacation for another couple of days and Inkfish is in reruns.

In a creature much simpler than a human, scientists have figured out how to erase a memory. Sea slugs that had received repeated electrical shocks learned to expect them again--until researchers gave the slugs an injection that returned them to blissful ignorance.

The fellow above is Aplysia californica, a hefty sea slug that's shown here releasing its mysterious magenta ink. (I suppose that makes it an honorary inkfish?) Researchers at UCLA used a tankful of these quarter-pound slugs to test the hypothesis that a certain molecule allows the slugs to store long-term memories.

At the beginning of the experiment, researchers tested the slugs' baseline sensitivity by poking them in the hind end with a broom bristle. This causes a slug to retract its siphon, a straw-like structure near the tail, for a second or two. Then they "trained" the slugs by giving them five sets of electrical shocks to the tail over the course of 80 minutes. Afterward, the slugs had learned the lesson that touches near the tail are bad. (Come to think of it, that may have been the title of a movie we watched in my fourth-grade health class). Twenty-four hours after their training session, the slugs still remembered; they retracted their siphons for 40 or 50 seconds when poked with a broom bristle. The reaction was almost as strong 48 hours after the training session.

(Two days may not seem like a very "long term" over which to remember that you were recently tormented by scientists. But short-term memory only refers to the items that we hold in our minds on the order of seconds. Anything we hang on to for longer than that is considered to be in our long-term memory.)

And then it was time for some Men in Black mind-erasing action. The molecule the researchers were interested in is called protein kinase M (PKM). A few minutes after the 24-hour test, they injected some of the sensitized slugs with a molecule that interferes with PKM and prevents it from doing its normal job--which is, in case you asked, adding phosphate groups to other proteins.

The results were straightforward and striking. At 48 hours, when the other slugs were still extremely reactive to being poked in the tail, those that had been injected with the PKM blocker were completely back to normal. Their siphon-retracting reflex was exactly what it had been before their training. The memory of the electric shocks they'd received seemed to be gone.

The scientists even tried reminding some of the slugs of their training. At 96 hours, they gave them one more set of shocks (as opposed to the five sets in the initial trial). The slugs seemed unimpressed, showing no change to their reaction.

In another experiment, the researchers left the slugs alone for a whole week after their initial shock training. On day 7, the slugs were still sensitized from their training, withdrawing their siphons for around 40 seconds when poked. Some of the slugs were injected with a PKM blocker at this point, a whole week after the training session. The next day, those slugs' reactions were right back down to zero. The un-injected slugs, though, still remembered their shocks.

The researchers also experimented on individual slug neurons--one sensory neuron and one siphon-moving neuron--that they removed from the slugs and kept in a dish. Again, they found that blocking PKM prevented the siphon neuron from retaining its "memory."

So what is PKM doing to neurons that makes it so critical to long-term memory? New memories involve the growth of connections between neurons, and the authors think the ongoing activity of PKM might be necessary to maintain these structural changes. Without housekeeping by PKM molecules, the connections are lost.

Researcher David Glanzman, who led the study, believes that understanding these processes could lead, in the future, to targeting and erasing specific memories in humans. "Almost all of the processes that are involved in memory in the snail [or sea slug] also have been shown to be involved in memory in the brains of mammals," he said in a press release.

It's a spooky idea, but erasing memories might be of help in treating post-traumatic stress disorder or drug addiction. The process might even be reversed to treat Alzheimer's disease, which is currently incurable. Let's hope that when that day arrives, someone remembers to thank the humble sea slugs.

Image: Genny Anderson/Wikimedia Commons

Cai, D., Pearce, K., Chen, S., & Glanzman, D. (2011). Protein Kinase M Maintains Long-Term Sensitization and Long-Term Facilitation in Aplysia Journal of Neuroscience, 31 (17), 6421-6431 DOI: 10.1523/JNEUROSCI.4744-10.2011

Kids Learn to Speak by Not Listening

Getting dressed in the dark is generally considered a bad idea. When presenting ourselves to the outside world, we like to have some visual feedback so we know what other people are seeing. Likewise, as young children learning to talk, we rely on auditory feedback--we need to hear ourselves speak. We continue to use this feedback, and adjust our talking accordingly, even as fully fluent adults. But at a certain stage of development, we may learn by not listening to ourselves at all.

Researchers led by Ewan MacDonald in Denmark tested Canadians of various ages on how they responded to auditory feedback while speaking. One group of subjects was adults; a second group consisted of kids around 4; and a third group was made up of toddlers around 2 years old. The study was simple: All the subjects had to do was say the word "bed" over and over. (The kids and toddlers were convinced to do this by playing a computer game. By saying "bed," they helped a distracted robot walk across a playground.)

Subjects wore headphones, and they heard normal feedback of their own words for the first 20 repetitions of "bed." But during the 30 repetitions that followed, the headphones began to lie to them. Subjects heard distorted feedback, so that what they pronounced as "bed" came back to them sounding more like "bad."

Adults and kids tried to compensate for this distorted feedback by changing the vowel they were saying.  Their "bed" became closer to "bid." But the toddlers didn't change what they were saying at all. They seemed to be speaking without listening to what they were saying. The robot was still crossing the playground, so visual feedback told them they were doing the right thing. Auditory feedback, on the other hand, was ignored.

You might expect toddlers to be listening a lot. But MacDonald speculates that when very young children are starting to talk, responding to the sound of their own voices might be counterproductive. Since toddlers' vocal cords are just getting accustomed to the sounds they need to make, listening to their own all-over-the-place babbling might not tell them much. Other kinds of feedback--say, visual responses from their parents--would give them a better idea of how they're doing.

Some support for this idea comes from language research in birds--not the kind that talk, but regular songbirds, which must learn complex vocal sequences in order to communicate and survive. MacDonald points to a study of brown-headed cowbirds, a small North American songbird, in which young males were raised by non-singing females. Without hearing songs to emulate, the young birds "nevertheless acquired mature, species-specific songs." Video recordings revealed that as the juvenile males sang experimentally, the adult females had given them visual feedback. This non-auditory response had been enough to help the birds learn. Like the cowbirds, human toddlers seem to rely on non-auditory cues for some part of their language learning.

Among the toddler group, hanging onto recruits for the duration of the experiment was a bit of a challenge. Out of 50 initial two-year-olds in the study, "Ten of the toddlers refused to talk and 13 refused to wear the headphones." Another six didn't speak consistently enough for the feedback system to work, and one toddler didn't manage to say "bed" at all.

This raises the possibility that the 20 toddlers who made it through the whole experiment were not representative of the group as a whole. They might have been the most proficient talkers, or the most mature. The authors argue that this shouldn't affect their results. Even if their subjects were the most mature toddlers, they say, those kids still didn't compensate for the vowels they were hearing, so the less mature talkers wouldn't have done any better.

But MacDonald doesn't address the possibility that these toddlers failed to compensate for altered vowels because they were more mature. Maybe talking without listening is a crucial developmental stage that must be reached, not just grown out of.

(Some adults, of course, seem to have never left the stage of talking without hearing themselves. Perhaps we should all stop nodding and smiling when they speak.)

MacDonald, E., Johnson, E., Forsythe, J., Plante, P., & Munhall, K. (2011). Children's Development of Self-Regulation in Speech Production Current Biology DOI: 10.1016/j.cub.2011.11.052

For Genitalia, Shape Matters (Not Size)

When it comes to a dung beetle's junk, size doesn't matter. At least, not to the process of rapid evolution that creates new species. Researchers say that what matters there, as males and females evolve together and distinguish themselves from related species, is shape.

Intercourse between Onthophagus beetles--the genus used in the current study, which includes the dung beetle O. taurus as well as other scarab beetles--is far from simple. It begins with the male climbing onto the female's back and inserting his penis's grabbing appendages (called parameres) into special pits on her underside. "For simplicity," the authors refer to the female's collection of equipment here as the "pygidial flap." Once the male has gripped the female tightly, he inflates his endophallus and--well, you know the rest.

Beetles and other arthropods are known to have quickly evolving genitals; often, the genitals are the key to telling similar species apart. So researchers wanted to know how this genital arms race affects the development of new species. In some cases, it really is an arms race--males evolve mechanisms that are more efficient at, say, piercing the female's abdomen and delivering sperm directly to its target, while females evolve mechanisms to protect themselves or regain control of the situation. Even in less sexually aggressive species, male and female genitalia should evolve together to ensure a good fit.

The authors looked at several species of Onthophagus with different degrees of relatedness. A species, despite what you were told in ninth-grade biology, is a bit of a squirrelly thing to define. It's often said that animals belong to different species if they are unable to interbreed--but in the wild, this breaks down. Three of the beetle species studied here belong to a "species complex," a closely related group whose members haven't totally separated from each other. The other species were O. taurus, an Old-World dung beetle, and its sister populations that have evolved since the beetle was introduced to other regions in the 1960s.

Since the paramere and pygidial flap are tightly locked together during beetle sex, the researchers looked here for the signature of evolution--rather than at the beetles' other copulatory organs that don't need to interact as closely. Across the several Onthophagus species in question, they analyzed the shape and size of parameres and pygidial flaps from several hundred beetles. Analysis was done by mapping "landmarks," such as boundaries between segments or inflection points of curves, onto images of the organs.

For consistency, poor lead author Anna Macagno mapped the landmarks on every one of these male and female bits (top and bottom, respectively) herself.

The tiny variations between all these very tiny private parts added up to a clear big picture: As species diverged from their relatives, male and female genitalia evolved together. But this evolution was primarily a change in shape. Size, for the most part, stayed the same.

Another way of understanding this result is that size does matter. Deviation from a standard size, perhaps because it leads to processes not working the way the organs' owners expect them to, is discouraged by evolution. Outliers don't pass on their genes. But when it comes to the shape of genitalia, evolution encourages experimentation. Male and female beetles that develop a new lock-and-key fit between their organs can quickly distinguish themselves from related populations. If other beetles' equipment is no longer compatible with yours, you've become a new species--and kicked others out of your gene pool.

What's impressive is the speed at which beetle populations can diverge like this. The O. taurus populations in the study have only been separated since the 1960s, when the dung beetles were introduced to new parts of the world. And even in the beetle species that still live in overlapping habitats, evolution is driving their genitalia in different directions. The quickest way to form a new species and exclude all your relatives, it turns out, may be to change the locks.


Images: Onthophagus bonasus Fabricus (not one of the species used in the study), Flickr/urjsa; bottom figure, Macagno et al.


Macagno, A., Pizzo, A., Parzer, H., Palestrini, C., Rolando, A., & Moczek, A. (2011). Shape - but Not Size - Codivergence between Male and Female Copulatory Structures in Onthophagus Beetles PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028893

Aesop's Crows Understand Physics, Literature

Aesop told the fable of a thirsty crow that came upon a nearly empty pitcher of water and discovered that by dropping pebbles in, he could raise the water to a drinkable level. The moral is "Little by little does the trick"--or was that "Necessity is the mother of invention"? Either way, scientists have enjoyed testing non-fictional members of the clever corvid family with this puzzle. Most recently, wild crows showed scientists they're smart enough for a whole barrage of Aesop-inspired challenges.

New Zealand psychologist Alex Taylor led the study of five New Caledonian crows that had been captured from the wild. The birds (Caesar, Laura, Bess, Mimic and Pepe, since you asked) were each given an extensive series of tests while visually separated from their peers. Like one of those computer games where you walk into a dead-end room and have to find the secret button that opens a submarine hatch and takes you someplace more interesting, the crows were presented with varied apparatuses and had to figure out which objects were tools that would help get a tasty treat into their beaks.

The tests began with the classic "Aesop's fable paradigm." Crows saw a tube partially filled with water. Inside the tube was a bite of meat, stuck onto a piece of wood that floated below their reach. Small stones were sitting nearby. If you're thinking that you might not have been able to solve this puzzle, rest assured--the birds didn't get it either.

After making sure the crows didn't naturally know how to solve the puzzle, the researchers gave the birds a hint. This time, the crows saw the same tube, floating meat, and stones. But there was a platform next to the top of the tube with a couple stones sitting on it, too. As the crows attempted to jam their beaks far enough into the tube to reach the meat, they tended to accidentally knock the stones into the tube. After doing this several times and noticing how the water level rose, all the crows eventually figured out the trick. They began dropping stones into the tube on purpose to get the meat.

Although this looks pretty clever, it's possible that the birds found the solution by simple association: "Stones mean food. Mess around with the stones, or put them near the food, and the food gets in my beak." So the researchers followed up with a series of puzzles that tested what the crows actually understood.

(Only four crows were used in most of the experiments--poor Bess, perhaps believing herself to be in one of those fables where the crow gets eaten by an alligator, was too afraid of the testing apparatus to participate.)

In one test, the crows were given stones of two different sizes. They quickly began ignoring the smaller stones in favor of larger ones, which raised the water level faster. (Laura, the smartypants of the bunch, never once used a small stone.) In another test, the stones were replaced with white chunks of rubber and styrofoam. Though they looked the same, the former item was heavy and useful, while the latter uselessly floated on top of the water. Again, the crows picked up on the difference, learning after a few trials to discard the styrofoam chunks and throw the rubber ones into the tube. In this video, you can see Mimic mastering the puzzle on his first try (and adorably peeking into the tube to make sure the meat is still there).

The crows seemed to understand what was important about the objects they were using as tools: bigger and heavier items would get the meat to them faster. But did they grasp what was happening inside the tube? To test the birds' understanding of the water in the tube, researchers showed them a tube of water next to a tube of sand. Both had the usual chunk of meat sitting on their surface, but throwing rocks into the tube of sand would accomplish nothing. The crows soon learned this, more or less, and dropped most of their rocks into the water tube. In this video, smartypants Laura ignores the sand tube entirely in her fourth trial. When the tube of water was paired with a tube of air, the crows again learned to put most of their stones into the water tube--though they dropped a fair number of stones into the air tube as well, apparently struggling to grasp that one clear substance wasn't the same as the other.

New Caledonian crows use sticks as tools in the wild to dig grubs out of holes, and showed here that they can learn to use other kinds of tools as well. This suggests that using tools, for the crows, is true problem solving and not just an ingrained behavior (like your dog kicking up imaginary dirt on the sidewalk after it poops). And the birds' performance with different sizes and shapes of "rocks" shows that they can adapt their tool use to various conditions--though they did struggle a bit with the tubes of air and sand. Buoyancy is tricky for everyone.

With the crow-and-pitcher paradigm nearly exhausted, maybe scientists will turn to Aesop's other fables for future studies. Are crows susceptible to flattery when holding pieces of cheese? Do foxes eat grapes (sour or otherwise)? And, of course, does slow and steady really win the race?


Images: Project Gutenberg/Wikimedia Commons; Taylor et al. (video screengrab)


Taylor, A., Elliffe, D., Hunt, G., Emery, N., Clayton, N., & Gray, R. (2011). New Caledonian Crows Learn the Functional Properties of Novel Tool Types PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0026887

Lessons from Kobe on Life's 3-Pointers

You might expect NBA players to know when and where to take their shots. They get paid millions of dollars a year to work out, avoid hitting their heads on door frames, and put the ball in the basket. Yet even years of training can't overcome a basic human superstition about our own behaviors: We believe that whatever just happened is about to happen again. If we stopped trusting in streakiness, we might all score more points.

Tal Neiman and Yonatan Lowenstein, researchers in Israel with a mysterious interest in professional American basketball, scrutinized play-by-play accounts of games from the 2007-08 and 2008-09 seasons. Their analysis included 291 NBA players and 41 WNBA players (indicating a good grasp of Americans' proportional interest in women's sports).

Specifically, the researchers were interested in decisions players make after hitting, or missing, a 3-point shot. After a successful 3-pointer, what are the odds that a player's next attempt is another 3 (rather than a 2-pointer)? What about after a missed 3-point shot?

For both men and women, the success or failure of a 3-pointer had a major influence on what their next shot was. After sinking a 3-point shot, NBA players attempted a second one 41% of the time. But after missing a 3-pointer, only 30% of follow-up shots were 3's.

The numbers were remarkably similar for women: 41% of shots attempted right after a sunk 3-pointer were also 3's, but that number went down to 34% after a missed 3-point attempt.

Men and women were so similar in their behaviors, in fact, that the researchers could pool their data for further analysis. But there was at least one major outlier, politely referred to as "the Most Valuable Player (MVP) of the 2007-2008 season." Although he didn't name that player, we can hear the authors' implied "cough, KOBE, cough." A big believer in his own hot hands, Kobe Bryant followed more than half of his sunk 3-pointers with another 3-point attempt. But after missing a 3-pointer, he tried again only 14% of the time.

Kobe or not, basketball players are clearly more eager to take a second 3-point shot after they've sunk the first one. And they're even more likely to line up a 3-pointer after making two in a row. Intellectually or just instinctively, they believe this to be a good strategy. But there's bad news: it's not. 

Professional players are, in fact, slightly less likely to hit a second 3-point shot after hitting their first one than after missing it. The difference is just 6%, and it might be due to overconfidence or to better defense. But players make the situation worse by assuming they're on a streak. (A player's decisions might be justified if his team as a whole scored more points when he attempted a second 3-pointer, maybe through rebounding or general intimidation. But this was not the case. And 2-point shots were equally successful after making or missing a 3-point shot.)

The authors say this is an example of "reinforcement learning." Like a dog that sits on cue or a laboratory pigeon that pecks at the right button, getting an immediate reward tells us we should repeat our behavior. The basketball players in this study are "overgeneralizing": they ignore what they've learned about a shot's likelihood of success in general, and respond only to the emotional reward of their last sunk shot. And like a rat in a maze getting a tiny electrical shock, players who miss a shot respond to the pain of that most recent experience.

Overgeneralizing is obviously hard to overcome. We're wired to learn by experience, and that might be what leads us to trust in streaks. A success makes us feel like we'll succeed again; a failure suggests more failure. But if we could remember that every shot on net is a new one, we might all (even Kobe) make better decisions.

Image: Keith Allison/Wikimedia Commons


Neiman, T., & Loewenstein, Y. (2011). Reinforcement learning in professional basketball players Nature Communications, 2 DOI: 10.1038/ncomms1580

Why Good Time Estimators Are Better at Math

Since most of us were never called on in class to answer a tough time-estimation question, or quizzed on the lengths of tones in milliseconds, we don't have a good grasp of our skill in this area. It's kind of exciting. You could be a prodigy and not know it! But a cold dose of reality comes from new research saying skill in time estimation is tied to mathematical intelligence. If you're not amazing at math, your temporal abilities probably aren't A-plus either.

Writing in PLos ONE, a group of Italian researchers describe a study done on 202 adults. The subjects listened to a series of tones through headphones, and estimated the length of each tone in milliseconds. ("We first made sure that participants knew that one millisecond is a thousandth of a second.") Tones ranged from 100 to 3000 milliseconds long. That's a tenth of a second to three seconds, for those of you who are non-amazing at math.

Everyone became more accurate as tones got longer. Unsurprisingly, it's easier to guess that a sound lasts for one second or three seconds than 100 or 200 milliseconds.

Subjects were also tested on their arithmetic skills, general intelligence, and working memory. All these tests came from a standard set of IQ questions. Arithmetic problems ranged from very simple ("What's 5 apples plus 4 apples?") to more difficult ("If 8 machines can finish a job in 6 days, how many machines are needed to finish it in half a day?"). To gauge non-mathematical intelligence, researchers gave subjects a verbal comprehension test (for example, "How are an orange and a banana similar?"). A challenge to remember strings of digits and recite them forward or backward tested subjects' "working memory," which is the ability to hold things in the mind and process them.

People's accuracy at guessing the length of tones was closely tied to their mathematical IQ. Less accurate estimators had lower math scores, and better estimators were better at math. But this connection didn't extend to general intelligence, or at least not to verbal intelligence: there was no relationship between subjects' estimation skills and their performance on the verbal comprehension test.

The researchers also found no relationship between time estimation and working memory. This is a little unexpected, since judging how long something took seems like a task for the short-term memory. And a previous study of time estimation did find a connection to working memory. But in that study, subjects did arithmetic problems while estimating times. The authors argue that making subjects do two things at once was a test of their working memory to begin with; subjects who excelled at estimating times while doing math problems would necessarily have a good working memory. In the new study, tasks were taken one at a time, and skill at time estimation seemed to be separate from working memory.

Subjects were also asked to rate their own mathematical ability on a scale of 0 to 10. These ratings followed the same pattern as math IQ scores: people who considered themselves as better at math were also better at estimating tone lengths. (Interestingly, out of the 202 Italian subjects, not one person rated himself or herself a 10. Does this indicate a general trepidation toward math? Some sort of cultural modesty? Surely in the U.S. someone would have claimed to be the best.)

Your sense of time, then, seems to be tied not to your intelligence or memory, but to your sense of numbers. The authors believe the connection lies in lines--the timeline and the number line. Previous research has shown that people use a mental number line to do math, sensing smaller numbers to the left and larger numbers to the right. People estimate lengths of time using another left-to-right mental path: small intervals are on the left, and larger intervals are on the right. (How would these experiments play out in a culture that reads right-to-left, or vertically?)

If it's all about lines, then mathematical and temporal skills may come down to a person's ability to judge increments, to arrange items in a path. Working with your mental timeline or number line, that is, may really be a spatial skill. And the best time estimators in the classroom might be the line leaders.

Kramer, P., Bressan, P., & Grassi, M. (2011). Time Estimation Predicts Mathematical Intelligence PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028621

Image: James Laing/Flickr

To Avoid Harassment, Guppies Swim with Sexy Friends

You know how it is: You're minding your own business when up swims a male guppy determined to copulate with you. It's not your fertile time of the month, you're not giving off attractive chemical signals, and you'd rather spend your time eating than pointlessly mating. But he just won't leave you alone.

Female Poecilia reticulata guppies have evolved a strategy for avoiding harassment and attack by single-minded males. Josephine Brask from the University of Copenhagen leads the team describing this strategy in a new study. It's a buddy system--but not the nice kind.

In the wild, females of P. reticulata (the Trinidadian guppy) swim in small groups called shoals. Males cruise from group to group in search of mates. Right after they give birth each month, females are interested in mating too; they release chemical cues into the water to make sure males get the message. But even when females aren't "receptive," males will pursue them and force them to mate. (Some fertilization does happen this way, thanks to sperm storage in the females, which might be why the behavior persists.)

The researchers guessed that female guppies could minimize harassment by sticking close to their more-fertile friends in the shoal. They tested this in several ways. First, they put male guppies in the center of a tank divided into three parts. On one side of him was a sexually receptive female guppy, and on the other side was a non-receptive female. The dividers in the tank were perforated so the male could smell the natural perfumes of his potential lovers. ("Males were isolated from females prior to testing [3-10 days] in order to increase their interest in females.")

As expected, males spent more time lingering at the wall of the receptive females. And non-receptive females who were paired with receptive ones got less attention from males. Even though a male guppy might harass an uninterested female when given the opportunity, he'll chose a more fertile partner if she's nearby.

Next, researchers tested which fish females prefer to hang out with. In a similar setup to the first experiment, female guppies had to decide between swimming near a sexually receptive female at one end of a tank and a non-receptive female at the other end. Females in their fertile time of month didn't care who they spent time near. But females in their less-fertile time preferred to hang around more-fertile females.

How can female guppies tell which of their shoal-mates are sexually receptive? Researchers repeated the choice test once more, but this time they replaced the fish on either end of the tank with streams of water. This water had been swum in by other female fish, and would contain any chemical signals those fish had released. The female guppies in the center of the experimental tank behaved just as before: non-receptive females preferred to hang around the water that smelled like receptive females, while receptive females didn't care one way or the other.

It seems, then, that female guppies are strategic about which other fish they spend time around. By swimming near females that are in their most fertile stage--that is, the most literally attractive to males--females that aren't ready to mate can save themselves some harassment. It might sound trivial, but for this strategy to have evolved, avoiding harassment would have to carry a real survival benefit. Male harassment is a burden, maybe because it saps females' energy, increases their stress levels, or just keeps them away from food.

If you're a human instead of a guppy, sticking near your more attractive friends will probably not help you avoid harassment--assuming you like your friends, anyway. Sending them ahead of you into a room might work, but being together can make things worse. And as anyone who's attended a bachelorette party knows, dudes in bars see a table full of women like unclaimed acreage on the frontier. The pioneer spirit kicks in.

A better way for human women to spare themselves sexual harassment (at least in my experience) is to be with other friendly men to begin with. Whether it's territoriality or stage fright, dudes seem to leave you alone if they see another Y chromosome in your vicinity. It's depressing, but it's also the point of this whole horny-guppy story: who you hang out with, whether you're a fish or not, matters to your own safety and survival. In a community, a herd or a shoal, the other individuals around you affect how you're perceived. You don't want to be the fattest zebra or the most attractive guppy. Sometimes, you just want your group to have your back.




Brask, J., Croft, D., Thompson, K., Dabelsteen, T., & Darden, S. (2011). Social preferences based on sexual attractiveness: a female strategy to reduce male sexual attention Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2212

Crab Eats Bacteria Grown on Hairy Arm Farms

When you live in near-blackness at the bottom of the ocean, you can't rely on plants to turn sunlight into food for you. The yeti crab, a pallid creature with woolly arms like an ill-conceived Muppet, eats bacteria that subsist on chemicals leaking from the seafloor. To keep things close to home, it gardens those bacteria in the lush fields of its own hairy forelegs.

Yeti crabs were first discovered in 2005, when a single representative of the species Kiwa hirsuta was dragged up from the ocean floor. In a new paper, Andrew Thurber from the Scripps Institution describes a second species of yeti crab. Researchers found clusters of Kiwa puravida crabs around methane-leaking seafloor cracks near Costa Rica. Like uncool concertgoers, the crabs were waving their arms rhythmically back and forth, as you can see in the video below.

These crabs, like the yeti crab discovered earlier, had a healthy population of bacteria living on their arms. Since some other invertebrates living around ocean vents are known to grow symbiotic bacteria on their bodies, the researchers investigated whether the yeti crab's bacteria were there for a reason (other than poor hygiene).

Circumstantial evidence suggested that the yeti crabs were not just tolerating their arm bacteria, but eating them. For one thing, scientists didn't observe the crabs scavenging, or attempting to eat any of the shrimp or other creatures sharing their ocean vent. For another, the crabs could be seen combing through their arm hairs with appendages by their mouths--then munching on what they found there.

Applying the principle that you are what you eat, the researchers analyzed fatty acids in the crabs' tissues and found a molecular signature matching their arm bacteria. These chemical-consuming bacteria seem to be not just a snack, but the primary food source for K. puravida.

As for the swaying behavior, Thurber guesses that it keeps a steady current of mineral-rich water flowing around the bacteria. Like farmers tilling and watering their fields, the yeti crab dutifully tends its crop by waving its bristly arms. And at harvest time, it doesn't have to take a step. That's pretty practical for a crustacean named after a mythical creature.


Image and video: Thurber et al., supporting information. Watch the video of a yeti crab eating its arm bacteria at your own risk.

Thurber, A., Jones, W., & Schnabel, K. (2011). Dancing for Food in the Deep Sea: Bacterial Farming by a New Species of Yeti Crab PLoS ONE, 6 (11) DOI: 10.1371/journal.pone.0026243