Field of Science


It's Harder to Dodge Sharks When Pregnant

Although it would be nice to hatch our babies from eggs Anne Geddes-style, or deliver them while still tiny and carry them around in a pouch, humans and other placental mammals are stuck lugging their developing fetuses inside their bodies. Luckily, most humans aren't in danger of predation. But for animals that sometimes have to run (or swim) for their lives, pregnancy can be dangerous.

In a punnily titled new study ("Pregnancy is a drag"), UC Santa Cruz researcher Shawn Noren investigates how pregnant dolphins are affected by carrying a wide load. Noren studied two captive bottlenose dolphins, each about 10 days away from giving birth, living in a lagoon in Hawaii.

Though the study only included these two dolphins, Noren collected many data points by having a scuba diver sit underwater and videotape the dolphins swimming back and forth. The dolphins were also observed and recorded periodically during the two years after they gave birth. By digitizing these videos, the researchers could quantify the dolphins' size, mass, surface area, swimming speed, and swimming mechanics.

As expected, very pregnant dolphins had a very much larger surface area. This created greater drag as the dolphins glided through the water. The dolphins also changed their swimming "gait," like a human who finds herself a little waddle-y in the final trimester. Dolphins get all their forward thrust from the up-and-down beats of their tails. The pregnant dolphins beat their tails a little more shallowly than usual, maybe because their muscles were stretched out and weakened by the fetus (or because their midsections were less flexible). Just like a human taking smaller steps, a dolphin making smaller tail-beats covers less distance. So the pregnant dolphins had to beat their tails faster to maintain a given speed.

Besides experiencing greater drag and a shortened "stride," pregnant dolphins have altered blood flow and lower lung capacity. They also store more lipid (fat) than usual in their blubber, making them extra buoyant. All these factors combine to slow a dolphin way, way down. The two pregnant dolphins in the study swam more than 60% slower, on average, before their calves were born. After recovering from pregnancy, the dolphins' average swimming speed was around 9 mph. But before giving birth, their speed was closer to 3.5 mph--similar to the pace of a walking human.

The crucial factor in avoiding predators such as sharks, though, is maximum speed. After pregnancy, the dolphins reached maximum swimming speeds of more than 14 mph. While heavily pregnant, they barely reached 8 mph. Of course, the researchers didn't introduce any sharks or killer whales into the lagoon to see how fast the dolphins could swim under real duress. But the researchers note that at the fastest swimming speeds they observed, pregnant dolphins would not have been able to out-swim most predators.

It's unknown whether pregnant dolphins are more vulnerable to predators in the wild. But among ungulates--hoofed mammals such as buffalo or wildebeest, which happen to be close relatives of whales and dolphins--pregnancy is a known risk factor for being eaten by lions. In dolphins, the greater effort needed to swim while pregnant probably means they need to take in more calories. But it also must make hunting for food more difficult. A pregnant dolphin will have a harder time chasing after quick prey or, because of her increased buoyancy, diving to hunt.

In humans, studies of how pregnancy affects walking have been inconclusive. This might be because there's a great deal of variation in how individuals' bodies adjust to pregnancy. These two dolphins, too, may not be representative of their whole species. But they demonstrate the amazing adaptability of a female mammal's body, whether she's diving for squid or just shuffling through the suburbs.

Noren, S., Redfern, J., & Edwards, E. (2011). Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus) Journal of Experimental Biology, 214 (24), 4151-4159 DOI: 10.1242/jeb.059121

Bacteria You'll Meet in a Public Restroom

Whether you're intentionally starting your Christmas shopping or you unwittingly get swept into Macy's by a tide of deal-seekers, you may eventually have to face a public restroom. You'll be sharing it not just with your fellow shoppers, but with a whole mess of bacteria species. Luckily, researchers in Colorado have done some digging into that mess so that you can know just who you'll meet behind the "Ladies" or "Gentlemen" sign.

Public restrooms are a great place to find bacteria, as the authors of the new study euphemistically put it, "because of the activities that take place there and the high frequency of use by individuals with different hygienic routines." Furthermore, different neighborhoods within bathrooms probably house different communities of bacteria. To perform a census on these hidden but lively communities, researchers sampled surfaces in six men's rooms and six women's rooms at the University of Colorado, Boulder. Genetic sequencing of these samples told them which species of bacteria were present. Out of all the bacterial types that turned up, there were 19 phyla of bacteria present in every bathroom.

(The fact that the researchers grouped bacteria into phyla is an alarming reminder of how diverse bacteria are. A phylum is a large grouping that can contain thousands of species. Humans, for example, are members of a phylum that contains every other backboned animal on Earth. In bacterial terms, one faucet handle may as well be a whole rainforest.)

The researchers sampled ten surfaces within the restrooms. These included the in and out door handles; in and out stall handles; sink faucet handles; toilet seat and flush handle; floor around the toilet; floor around the sink; and soap dispenser. The 19 common bacterial phyla they found could be grouped into three communities.

Bacteria from human skin
The surfaces in the bathroom drawing above are shaded blue according to how rife they were with bacteria that live on human skin. Actually, these bacteria were common on all the surfaces studied here. But they especially dominated surfaces touched by the hands, unsurprisingly.

Bacteria from the human gut
Above, the same drawing is shaded to show the communities of gut-related bacteria. They're most common on the toilet surfaces (remember that in biology, "gut" usually means "feces"). People could have contaminated these surfaces by touching them with dirty hands or with actual feces. Additionally, a flushing toilet could spray and splash contaminated water onto the toilet's outer surfaces.

Bacteria from dirt
The bathroom floors harbored the most diverse communities of bacteria--not surprising when you think about all the other microbial communities your shoes travel through on their way to the restroom. Many of the bacterial types found on the floor were soil dwellers. This community also appeared on the toilet flush handle, perhaps from cautious patrons flushing with their feet.

The types of bacteria found in men's and women's restrooms were pretty much the same, but there were some differences in the proportions of those bacteria. Most notably, women's rooms had greater populations of Lactobacillaceae, a bacterial family that includes species living in the human vagina. The bacteria were found on and around the toilet, presumably having been spread there through urine and dirty hands. (Ladies: Please stop peeing on the seat.)

Of course, the reason all these bacteria are in the bathroom is that humans are crawling with them to begin with. The mere presence of bacteria, while unnerving to think about, isn't anything out of the ordinary. But some of these bacteria, especially ones coming from the gut (remember: feces), can cause disease. The study shows that gut bacteria end up throughout the bathroom, instead of confining themselves to the toilet bowl. Skin bacteria such as staph can also cause disease; a public restroom, like anyplace touched by a parade of strangers throughout the day, is covered with them.

All this bacterial diversity seems like a good argument for hands-free technologies in public restrooms. The fewer things you touch, the less chance you have to spread your bacteria around. (Paper towels, though, remove more bacteria from hands than blow dryers do.) Until they figure out a way to remove the public from public restrooms, regular soap and water is the best way to protect yourself from disease-causing bacteria--strangers' or your own. And seriously, stop peeing on the seat.

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Images: Flores et al. 

Flores, G., Bates, S., Knights, D., Lauber, C., Stombaugh, J., Knight, R., & Fierer, N. (2011). Microbial Biogeography of Public Restroom Surfaces PLoS ONE, 6 (11) DOI: 10.1371/journal.pone.0028132

I'm a Synesthete. Is Something Wrong with Me?

Like victims of catastrophic head injuries, people with synesthesia often appear in neuroscience papers identified only by their initials to illustrate the mysteries of the brain. But synesthesia's not a freak occurrence. It's estimated that 2-4% of people have abnormal connections between their senses. The condition may not be an accident at all, but a trait that evolution has retained for a reason.

The authors of a new review paper, David Brang and V. S. Ramachandran, ask why synesthesia has survived. Since it runs in families, synesthesia seems to be partially genetic. But it appears in many different forms--more than 60 have been documented. Garden-variety synesthetes see numbers, letters, or sounds in specific colors. Less commonly, synesthetes may experience each day of the week as a certain point in space, or feel touches on their own bodies when seeing another person touched. Many genes may be involved, and the interaction between synesthesia genes and a person's environment might lead to all kinds of outcomes.

It's possible that the genes promoting synesthesia have been kept around by evolution because they have a "hidden agenda." Another such trait, Brang and Ramachandran say, is sickle-cell anemia, which in addition to its unhelpful medical effects grants protection against malaria. Aside from the obvious sensory quirks, do synesthetes have a sneaky superpower?

Ramachandran, incidentally, is the person who broke the news to me about my own synesthetic tendencies. During my freshman year in college, my friends and I went to a talk he was giving on campus. We settled into folding seats, ready to hear about an exotic cognitive phenomenon. "For someone with synesthesia," Ramachandran explained to the auditorium, "the number 3 might always appear as red."

Lame. I leaned toward my dorm-mates. "But 3's are green," I whispered. They turned to stare at me. "Oh," I said.

Ramachandran then projected a screen full of 5's and 2's, printed as if on a digital clock, square-edged reflections of each other. I was distracted by a weird illusion: Although the numbers were all in black, there were flickers of maroon and navy wherever I wasn't looking, like the gray blobs that appear in your periphery when you look at a grid of black squares. I wondered if I was seeing a trick of light from the projector. Then I heard Ramachandran explaining, as he moved to the next slide, that this was a test for synesthetes, who could discern a hidden pattern among the 5's and 2's more easily because of their associated colors. Ohh, I thought.

Brain research has only begun to figure out what's happening inside a synesthetic brain. For grapheme-color synesthetes (people who associate numbers or letters with colors), seeing those numbers or letters  activates a color-perceiving brain region called V4. This shows us the connection is happening on a sensory level, and not in the realm of abstract ideas. A number doesn't just remind a synesthete of a color; it triggers a color-sensing area in the brain.

A recent paper suggested that the visual centers of grapheme-color synesthetes are hyperexcitable, responding to only a fraction of the stimulation needed for non-synesthetes. Perhaps relatedly, some researchers think synesthesia comes from lazy pruning in the brain. During development, the brain trims out extra neural connections to keep everything running efficiently. But synesthetes may have given their brains' gardeners too many days off, and the resulting overgrowth may link brain centers that shouldn't be related.

So what superpower could an overactive and underpruned brain have? Synesthesia is more common among artists, and synesthetes tend to be more creative than others. Maybe today's artists were a previous era's tool-builders, chipping stones into new shapes and getting a bigger share of mastodon meat in return. Or maybe evolution has never selected for artists, and creativity is just another side effect of the synesthesia genes.

As a more convincing superpower, synesthetes might have enhanced sensory perception. Grapheme-color synesthetes, for example, are especially good at detecting colors. Synesthetes in general also have improved memories. This especially applies to something like a telephone number, which can be easier to remember because of its associated colors. But if synesthetes' better memories extend to other kinds of sequences or details, that trait could have given them an evolutionary boost in the past. Synesthesia genes might indirectly help people perceive and remember their environments--or the experience of synesthesia itself might be what helps them.

Personally, I've never noticed any sort of benefits (unless you count my brief and uncool foray into pi memorization in eighth grade). But synesthesia is good for an embarrassing moment now and then, such as during the occasional poker games I've played with friends. The problem with poker is that I can hear a hundred times how a green chip is worth 25 (imaginary) dollars or a blue is worth 10, but I'm never going to believe it because those colors don't fit the numbers. Other people have to help me place bets because doing arithmetic with poker chips stumps me.

I discovered a similar pitfall when using some DNA sequencing software for my college senior thesis. Our machine read the sequence of DNA bases and returned a series of A's, T's, G's and C's. But instead of just a string of letters, the data took the form of a series of colored peaks:

Whenever the computer was uncertain about the sequence, I had to double-check the peaks and enter the corresponding letters myself. Now, I'm not the only person who thinks A's are red; it's a common association among synesthetes. But in this software A was green. The other three letters were also wrong--almost perversely so, it seemed to me. I had to check the key another time with every base I entered. My advisor probably thought I'd had a stroke when he saw how badly I was struggling to memorize a simple four-letter code. When I put my head in my hands and groaned that T isn't red, it's just as blue as the number 2 is, he abandoned me at the computer. "I don't know what you're talking about," he said over his shoulder.

Finding out more about the mechanics of synesthesia would give researchers insight into the working of the brain in general. Besides the obvious open questions (like what causes synesthesia and how it works), the authors point out some other areas for research: Does synesthesia exist in animals? Does everyone in the population fall somewhere on a spectrum of synesthesia? Do the genes causing synesthesia independently boost memory or sensory abilities--or does synesthesia itself benefit mental abilities somehow? And although numbers and letters can evoke colors, why is it never the other way around?

As much as I'd love to have a superpower, I'll settle for being mildly interesting to neuroscientists while having a brain that's in one piece. And avoiding poker games.

Image of grapheme colors: Brang and Ramachandran, doi:10.1371/journal.pbio.1001205.g001. (I did not draw this picture.)

Brang, D., & Ramachandran, V. (2011). Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words? PLoS Biology, 9 (11) DOI: 10.1371/journal.pbio.1001205

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Synesthesia and the Excitable Brain

To people whose sensory perceptions stay quietly inside their own sandboxes instead of coming out to play with each other, it will come as no surprise that synesthetes--people who experience letters with colors, or sounds with tastes--have something paradoxical going on in their brains.

"Grapheme-color" synesthesia is the most common variant of the condition. These synesthetes associate letters and numbers with particular colors; for example, a person might consistently experience the color  green with she sees the letter Q, or blue for the number 4. Since grapheme-color synesthetes are also especially good at telling colors apart, researchers at Oxford guessed that these people are extra-sensitive in the visual centers of their brains.

The researchers used magnetic stimulation to tickle the visual cortices of synesthetes' and non-synesthetes' brains. Passing a certain threshold of stimulation causes people to see flashes of light called phosphenes. In this experiment, normal people needed three times as much stimulation as synesthetes before they began to see phosphenes. In other words, as predicted, the visual cortex of a person with synesthesia is "hyperexcitable"--it's more easily stimulated than the brain of a non-synesthete.

(As a control, the researchers tested how much brain stimulation it took before subjects' hands started twitching. The threshold was the same for synesthetes and non-synesthetes. But just thinking about this experiment exceeds my threshold for the willies.)

What does hyperexcitability in the brain have to do with synesthesia? The obvious hypothesis is that it immediately causes synesthesia: People with overly sensitive visual centers in their brains have experiences of color that are below the level of consciousness for normal people.

To test this, the researchers did some more brain stimulating while they had synesthetes perform a task to trigger their synesthesia. Subjects were shown a number followed by a color and asked to name the color. If the real color matched the color they automatically perceived with the number, subjects could identify the color more quickly; if the colors didn't match, subjects made more mistakes.

The researchers used two different types of stimulation on subjects' brains. One type of stimulation increased excitability, making their visual cortices even more sensitive than usual. The other type of stimulation would have the opposite effect, quieting down the hyperactivity in their brains.

If hyperexcitability were causing the experience of synesthesia, then stimulation that increased excitability should make subjects even more synesthetic, while stimulation that quieted the brain should make them more normal. But the opposite was true. When their visual cortices were less excitable, subjects experienced more powerful synesthesia than usual (as measured by their performance on the color-naming task).

So even though synesthetes have hyperexcitable brains, toning down that excitability actually makes them more synesthetic. Luckily, we don't all have to overwork our own brains trying to resolve this paradox: the authors have a hypothesis.

People born with hyperexcitable visual centers, the authors say, may develop grapheme-color synesthesia when they're very young. Because their brains are extra sensitive to visual stimuli, the symbols and colors around them get tied together abnormally in their perception.

But as those synesthetes mature, their brain areas become more specialized. The synesthesia is locked in, and the hyperexcitable visual cortex no longer drives it. Instead, all that extra noise in the brain drowns out the synesthetic effect somewhat. So when the overactive parts are quieted down, as in this study, the synesthesia comes through even more clearly than usual.

This was a small study, and even if the theory accurately describes the synesthetes involved, it might not apply equally to others. The experience of synesthesia can vary widely between people. But if the hyperexcitability theory is true, then this weird paradox might be a kind of blessing to synesthetes. As it is, synesthesia isn't considered a disorder or hindrance; it's just a colorful quirk. If the very brain feature that created their synesthesia weren't now drowning it out, though, maybe synesthetes would experience the world as an overwhelming sensory carnival.

Terhune, D., Tai, S., Cowey, A., Popescu, T., & Cohen Kadosh, R. (2011). Enhanced Cortical Excitability in Grapheme-Color Synesthesia and Its Modulation Current Biology DOI: 10.1016/j.cub.2011.10.032

Do Voters Prefer Lower Voices?

In apparent bad news for squeaky-voiced politicians, researchers at McMaster University say that voters prefer male candidates who speak at a lower pitch. In better news, their study involved no actual voters or candidates. So is it just laboratory lore, or is there some truth to this theory?

The study consisted of two experiments. In the first, 125 young men and women listened to a series of audio clips. The clips were taken from archived recordings of nine U.S. presidents, tweaked to create both a lower-pitched and higher-pitched version. In each trial, a subject listened to the two versions of one president's voice, then answered questions: Which of the two voices sounds more attractive? Which sounds more intelligent? Which would you be more likely to vote for?

The subjects chose the lower voices for all nine questions about positive attributes, and only selected the higher voice as that "more likely to be involved in a government scandal." But all this really says is that when subjects were presented with two recordings of the same person's voice, side-by-side, they consciously preferred the lower-pitched version.

To really get at people's voting preferences, the study should have kept subjects in the dark about what they were selecting. The audio clips should have been randomized so that subjects were comparing different people, not different versions of the same voice. The words spoken in each recording should have been the same. Naturally pitched voices could have been included, instead of only altered voices. As long as voices were being altered, it would have been nice to include several different pitches, instead of only two. And as long as we're changing the study altogether, how about some historical data about the voices of winning and losing candidates in actual elections?

The second experiment was a little better. Instead of presidents, subjects heard the voices of six non-famous males, manipulated into higher- and lower-pitched versions, speaking the same sentence. (Don't get too excited; there were only 40 subjects this time.) In each trial, subjects heard one raised voice and one lowered voice, then chose which one they would rather vote for in a national election.

Again, subjects picked the lower voices. But again, subjects were being asked to choose between an obviously lower and higher voice. If the voices had been presented one at a time, and subjects asked to rate them individually on attractiveness or leadership or appeal to voters, we could glean more information about people's unconscious preferences. As it is, we only know that subjects consciously preferred men with lower voices, deeming them better leaders and (according to attractiveness ratings) better potential mates.

Lead author Cara Tigue suggests that since a lower voice in males corresponds to higher testosterone levels, people who prefer basses to tenors are really displaying a preference for hormone-heavy men. Perhaps, Tigue says, we've evolved to prefer dominant men, and to detect them based on their vocal pitch.

It would be hasty, though, to infer anything from this study about the evolution of democratically elected pack leaders. Maybe if we elected more female politicians, people would stop associating a low voice with leadership ability in the first place.

Meanwhile, as Tigue acknowledges, there are a lot of factors that matter more to an election than vocal pitch. This year's candidates would be better off worrying about their talking points than the pitch at which they're delivered.

Cara C. Tigue, Diana J. Borak, Jillian J.M. O'Connor, Charles Schandl, & David R. Feinberg (2011). Voice pitch influences voting behavior Evolution and Human Behavior

Image: Screenshot from

Hell Hath No Fury like a Hermaphrodite Shrimp

Like car wash attendants for the coral-reef crowd, Lysmata shrimp staff "cleaning stations" where fish can go to be shined up. At these stations, cleaner shrimp eat parasites and dead tissue off the bodies of their clients, while the fish repay the act by not eating the shrimp. Some cleaner shrimp species, such as L. amboinensis, live and work in monogamous, hermaphroditic couples, faithfully fertilizing each other's eggs during their off-hours. In order to arrive at these peaceful unions, however, they might have to do a little killing.

Researchers Janine Wong and Nico Michiels in Germany wanted to know how L. amboinensis ends up in pairs rather than groups. When everybody has all the equipment necessary to spawn more shrimp, why is two the best number to live in?

The researchers collected cleaner shrimp subjects and kept them in tanks one, two, three, or four at a time.  No matter how many roommates they had, all the shrimp were given plenty of food and an equal amount of space. Then the researchers sat back to watch.

After six weeks, they found that every group of three or four shrimp, without exception, had become a pair of shrimp. Every pair of shrimp had remained a pair. To get rid of extraneous mates, the shrimp had killed each other until there were only two left.

Since the researchers had grouped the animals by similar size, though, no shrimp could just walk up to another and tear its head off. They had to wait for an opportunity.

Like other arthropods, cleaner shrimp periodically molt, shedding their old exoskeletons and growing new, better-fitting ones. Right after molting, which happens overnight, they're soft-bodied and vulnerable. In the experiment, the cleaner shrimp acted benignly toward each other during the day--but whenever the researchers returned in the morning to find a dead shrimp, its just-molted shell was in the tank with it. "Analysis of nighttime videos," the authors write, "indicated that aggressive interactions [had] contributed to mortality events."

Perhaps sensing the danger, shrimp living in groups of three or four suppressed molting, shedding their exoskeletons less often than usual. Once they were in stable pairs, the shrimp could relax and return to a regular molting schedule.

Competition for food could be behind L. amboinensis's urge to live in pairs. The more shrimp occupy a cleaner station, the fewer parasites and dead fish scales there are to go around. Having just one partner gives shrimp the minimum requirement for reproducing and the maximum share of food.

Another theory, called sexual allocation, says that species will find the optimal balance of males and females. This is true of male and female individuals within a population, as well as male and female functions within a hermaphroditic individual. Generally speaking, sperm are cheap for a body to make, while eggs are expensive. This means that a hermaphrodite should invest as much energy as possible into making eggs. If a shrimp is competing with others to reproduce, it'll have to make a lot of sperm to maximize its chances of fertilizing some eggs. But if a shrimp only has one partner, it knows its sperm have no competition--so it can get by with the minimum investment in sperm, and devote more energy to eggs.

The authors point out that the shrimp murders they witnessed took place under unnatural circumstances. On a real coral reef, cleaner shrimp getting bad vibes from their neighbors might just move away, rather than wait to be killed in the night. In enclosed laboratory tanks, the shrimp were forced to take drastic measures to reduce their group numbers. Still, the story ended the same way in all 20 tanks containing extra shrimp; this suggests the impulse to kill didn't come out of nowhere.

It's possible that in the ocean, the shrimp rarely (or never) act on their murderous tendencies. But someone would have to put cameras in the coral reefs to find out whether Lysmata's life is as much of a soap opera as it seems.

Image: Wikimedia Commons/Chris Moody

Janine W. Y. Wong, & Nico K. Michiels (2011). Control of social monogamy through aggression in a hermaphroditic shrimp Frontiers in Zoology

This post has been submitted to the NESCent contest for a travel award to attend the Science Online 2012 conference.

Make Mine Well-Done (with a Side of Calories)

Unless you enjoy your beef patties uncooked and straight from the fridge, there may be more calories hiding in that hamburger than you think. Harvard researcher Rachel Carmody says that our standard method of measuring calorie content doesn't account for the ways heat changes food. Cooking adds calories, Carmody says, and she's got some Atkins-adherent mice to back her up.

The calorie numbers on food labels are calculated according to how many grams of fat, carbohydrate, and protein the food contains, and how calorie-dense each of those nutrients is. It's simple math and chemistry. But since calories are a unit of energy--how much energy you, as an eating animal, manage to extract from your meal--biology should be a part of the equation, too. Our standard calorie math doesn't consider how much energy we expend chewing and digesting our food, or what components of our meal go toward feeding our gut microbes instead of our bodies. It also ignores the effect of cooking: heat breaks down starches and unravels proteins, making those molecules easier for our bodies to absorb.

Carmody used mice to study the effects of an all-cooked or all-raw diet. Mice, like humans, are natural omnivores. Unlike humans, they will allow you to feed them nothing but raw sweet potato for four days.

Adult male mice were put on a diet of either sweet potato or beef, raw or cooked. (The researchers also studied the effect of pounding the food, which makes it easier to chew but doesn't otherwise have much effect.) The mice could eat as much of their one food as they wanted. They were also free to exercise, running on magnetic wheels that recorded how much use they got. The researchers measured how much food their subjects ate, how much they exercised, and how much weight they had gained or lost after four days.

Since previous research had shown that cooked starches provide more energy, the potato-eating mice were expected to get more calories from their food when it was cooked. Obligingly, the mice maintained their original weights on a cooked-potato diet but lost weight on a diet of raw potato. Besides getting more energy out of each bite of food, the cooked-potato mice also ate more. The raw-diet mice, on the other hand, apparently weren't able to choke down enough sweet potato to keep up their weight. Both groups of mice exercised the same amount.

Mice being fed lean beef were also expected to lose weight, lacking necessary fat and carbohydrates in their diet. (The authors point out that in humans, eating nothing but lean meat leads to a condition called "rabbit starvation." You can go ahead and cross that all-rabbit diet off your list of resolutions for 2012, because it's said to cause diarrhea, headache, and "vague discomfort.")

All of the meat-eating mice lost weight. But those mice eating cooked meat lost significantly less weight, demonstrating that they were able to get more calories out of their food. Their amount of exercise was the same as the raw-meat mice. And unlike the mice fed on sweet potato, the meat-eating mice actually ate less of their food when it was cooked. This suggests that they weren't enjoying their diet very much, but it also suggests that the cooked beef was even more calorie-rich than the weight results would imply. If the mice eating cooked beef had swallowed the same quantities as their raw-diet counterparts, they might have lost even less weight, or not lost weight at all.

There are several factors that could make cooked meat more energy-rich. High heat unwinds (or "denatures") protein molecules, making them easier to digest. Since cooked meat is usually softer, we need to expend less energy chewing it up and breaking it down inside our bodies. Additionally, cooking kills the pathogens that like to hang out on raw meat. When we ingest E. coli or Salmonella along with our meal, we have to divert extra energy to our immune systems to keep those bacteria at bay. Calories spent chewing, breaking down, or disinfecting our food cancel out the calories of energy we're taking out of it.

We started using fire at least 300,000 or 400,000 years ago. For reference, that's before modern humans even existed. As long as we've been Homo sapiens sapiens, we've lived with fire. Once we figured out how to cook our food, which included a lot of meat, we would have seen the benefits: more energy for making tools, raising families, and growing those big brains.

Now that meat is available to many of us in the form of daily Double Whoppers, and not just the occasional mastodon steak, the question of how many calories are really in our food isn't a trivial one. Even the most careful calorie counters may be taking in more energy than they think. A fast-food taco, or a trough of starchy pasta at a restaurant, could hold even more calories than the menu says.

We need better math, for everyone's sake. For starving and malnourished populations, understanding how cooking increases calorie content could help people glean more sustenance from their limited resources. For populations struggling with obesity, better food labeling could allow people to take control of their calorie intake before we all have to go on a rabbit diet.

Carmody, R., Weintraub, G., & Wrangham, R. (2011). Energetic consequences of thermal and nonthermal food processing Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1112128108

Image: Carmody et al. 10.1073/pnas.1112128108

Which Ancient Megafauna Did We Wipe Out?

If things had turned out differently in past millennia, modern-day animal lovers wouldn't have to fly to Kenya to go on safari. North America was once overrun with tourism-worthy animals: Aside from the iconic woolly mammoth, there were saber-toothed cats, giant sloths, and short-faced bears more than twice as massive as a grizzly. We're still not sure what happened to them, but a new study in Nature attempts to untangle the whodunnit.

Since dozens of these "megafauna" species disappeared from the Americas, Eurasia and Australia just as humans were arriving, it's tempting to blame ourselves. The human love of the mixed grill, after all, runs deep.

But the mass extinction, beginning around 50,000 years ago, coincided with another key event: the end of the last ice age and shift to a warmer climate. So controversy over what killed off the ancient megafauna has persisted.

To tackle the large-scale, globe-spanning question, a large and globe-spanning team of researchers decided to take it species by species. Even though the animals went extinct around the same time, they might have been individually done in by different factors. The researchers looked at ancient animal remains and human remains from around the world, as well as DNA samples from the megafauna. The genetic material told them about each species' diversity over time (species with more genetic diversity are better able to adapt to changing environments), and the overlap of human and animal remains showed when and where we coexisted.

Woolly rhinoceros: Not our fault.

The study focused on just six animals. All of them were herbivores living in North America or Eurasia, and some of them have living members today but inhabit a greatly reduced range. 

The woolly rhinoceros, pictured above, used to live in Eurasia but is now extinct. The researchers found that the woolly rhino's population size was actually increasing well after the species came in contact with humans, and there's no evidence that we commonly preyed on (or even came in contact with) the rhino. This would seem to vindicate us--it was probably the warming climate, not humans, that wiped out the woolly rhinoceros.

Wild horse: Our fault.

The wild horse or tarpan, Equus ferus, is also extinct today (and not to be confused with wild populations of domestic horses). The species maintained a large Eurasian population well into the warming period, suggesting that climate change wasn't what ultimately killed it. The overlap between wild horse and human populations, as well as the abundance of wild horse remains at human archeological sites, hints that we may have hunted the species to death.

Woolly mammoth: ?

As for the poor mammoth, the data are disappointingly unclear. Our ranges overlapped in both Eurasia and North America, and ancient North Americans are known to have hunted the mammoth. But the mammoth's population in Eurasia, like the woolly rhino's, was still increasing after it came in contact with humans, and its range may have begun to shrink as the weather warmed. It could have been either culprit that ultimately killed the mammoth, or a fatal combination of human hunting and climate change together.

That fatal combination is what makes this sort of research--the cold cases of paleontology, if you will--urgent today. We're again experiencing warming, though it's happening much, much faster than in the age of the mammoths. Simultaneously, we're pushing species out of their habitats or poaching them into extinction. The authors of the new study didn't find any one feature, such as a genetic signature or a distinct pattern of distribution, that predicted which animals lived and which died. That means we're no closer to guessing which of today's species will survive climate change and human involvement--like the reindeer, which lived through the extinction of its fellow megafauna and thrives today--and which will go the way of the mammoth.

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Images: PLoS/Mauricio Anton

Lorenzen, E., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K., Ugan, A., Borregaard, M., Gilbert, M., Nielsen, R., Ho, S., Goebel, T., Graf, K., Byers, D., Stenderup, J., Rasmussen, M., Campos, P., Leonard, J., Koepfli, K., Froese, D., Zazula, G., Stafford, T., Aaris-Sørensen, K., Batra, P., Haywood, A., Singarayer, J., Valdes, P., Boeskorov, G., Burns, J., Davydov, S., Haile, J., Jenkins, D., Kosintsev, P., Kuznetsova, T., Lai, X., Martin, L., McDonald, H., Mol, D., Meldgaard, M., Munch, K., Stephan, E., Sablin, M., Sommer, R., Sipko, T., Scott, E., Suchard, M., Tikhonov, A., Willerslev, R., Wayne, R., Cooper, A., Hofreiter, M., Sher, A., Shapiro, B., Rahbek, C., & Willerslev, E. (2011). Species-specific responses of Late Quaternary megafauna to climate and humans Nature DOI: 10.1038/nature10574

Spiders Seek Balance of Work and (Fore)play

When picturing animals at play, you probably think of frolicking otters or wrestling tiger cubs--not arachnids aligning their copulatory organs. But University of Pittsburgh researcher Jonathan Pruitt believes that pretend sex between Anelosimus studiosus spiders is a form of play. And, like those wrestling cubs or human toddlers making block towers, the frisky young spiders are gaining skills that will help them in their adult lives. If they devote too much time to play, though, male spiders may never get to experience the real thing.

A. studiosus lives and builds its webs throughout North and South America. The males reach maturity first and leave their homes in search of females. Upon finding a juvenile female spider sitting in her web, a male moves in. While he waits for his love interest to reach sexual maturity, the claim-staking spider attempts to fight off any other males that come by.

But that's not the only activity that fills his time. The male and female engage in courtship and mock copulation--or, as Pruitt puts it, "non-conceptive sexual behavior." Though the female's genital tract is, physically, not open for business, she assumes a "receptive posture" and allows the male to place his parts next to hers.

Lest you suspect that the males are merely a little dim, and keep trying to mate despite the females' physical unavailability, Pruitt explains that mock copulation has clear differences from the real thing. For a start, the spiders are less aggressive with each other than during real sex. Additionally, mock copulation is much less likely to end with the male being eaten. In a real sexual encounter, the male has nearly a 1-in-4 chance of being cannibalized by the female before the deed is done. But males survive almost 99% of dry runs without becoming a meal.

According to Pruitt, this behavior meets criteria for animal play: it takes place in non-stressful situations; it happens frequently and voluntarily; it mimics a functional behavior but doesn't accomplish the same function. In this case, the function that's not being achieved is actual intercourse. But there are other benefits for the mock-mating spiders. Once they mature, pairs in which at least one individual is "experienced" get the job done faster than inexperienced pairs. This presumably helps the male's chances of not being eaten. Experienced males are also less likely to be rejected--or chased out of the web--by females. And experienced females, after they mate for real, lay sturdier eggs.

Pruitt and his colleagues wanted to know which spiders were most likely to engage in pretend copulation, and what the tradeoffs were for those spiders.

The researchers captured baby spiders and grew them to maturity in the lab. By pairing the spiders up and observing how much space they gave each other, the researchers could score each spider's "personality" as docile or aggressive. To study mock copulation, the researchers dropped male spiders onto the edges of female webs and watched each pair for a total of eight hours, counting how many pseudo-sexual encounters occurred. Finally, they dropped new (inexperienced) male spiders onto some of those webs and watched the ensuing face-offs between males.

They found that a spider's propensity for fake mating depended on several factors. Docile spiders were more likely to engage in mock mating when their female partners were large. That's not what one might expect from a species prone to cannibalism, but apparently the males are enticed by large females' greater egg-laying potential.

Among aggressive male spiders, on the other hand, female size didn't matter. Their likelihood of mock copulation only depended on whether their bodies were in good condition.

Aggressive males were also more likely to win competitions with other males, forcing intruders to retreat from their webs. But male spiders that had engaged in a lot of pretend sex, apparently worn out, were less likely to win these duels.

Thus, as Pruitt puts it, "males that engage in the behavior excessively risk exhausting themselves and being supplanted by cohabitating interlopers." (Words to live by.) Though females may mate with multiple males, the male that gets to her first will father most of her offspring. So getting kicked out of one's web by an intruder, even temporarily, can have a high cost.

Is mock copulation in spiders a form of play, or of practice? For animals, they may not be substantially different things. A definition of human play would have to include fun. But whether we're looking at a dolphin or an invertebrate, we can't truly know whether an animal is enjoying itself. Whatever the spider is doing, it's clear that pretend sexual encounters can increase its reproductive success and evolutionary fitness. Unless the male spends too much energy entertaining itself, of course, in which case it may never get to demonstrate its prowess.

Pruitt, J., Burghardt, G., & Riechert, S. (2011). Non-Conceptive Sexual Behavior in Spiders: A Form of Play Associated with Body Condition, Personality Type, and Male Intrasexual Selection Ethology DOI: 10.1111/j.1439-0310.2011.01980.x