Leaping Land Fish Has Perfect Camouflage, Is Not a Hoax

You might never spot them if not for the jumping. On the coast of Guam, Pacific leaping blennies blend in perfectly with the rocks they live on, their limbless bodies maintaining a sleek profile. But the creatures give themselves away when they coil their tails to one side and shoot like a spring from rock to rock. These unsettling animals are fish that live on land. How they pull it off could give us hints about the evolution of our first earthbound ancestors.

Terry Ord, an evolutionary ecologist at the University of New South Wales, calls the Pacific leaping blenny "an extraordinary animal." It lives its adult life out of water, hopping between rocks and breathing through its skin as well as gills. It relies on splashes from waves to stay wet, but it rarely—or never—goes for a swim.

Even though the coast of Guam teems with leaping blennies, Ord says, "we know surprisingly little about this land fish." Ord and his graduate student Courtney Morgans investigated one mysterious feature: the fish's conveniently rock-like coloration. Without being so well camouflaged, could the blennies have ever made their first leap onto land?

Morgans and Ord traveled around the periphery of Guam and visited five different blenny populations. At each site, they took photographs of the fish and their background rocks. (The blennies aren't always stone-colored; during courtship, males darken to a charcoal hue while females fade nearly to white. Both sexes can flash a bright-red fin on their backs that they normally keep hidden. But the researchers kept a close eye on their subjects during the experiment to make sure they didn't change colors.)

Computer analysis of the photos showed that the blennies' normal skin color is a perfect match to the rocks they live on. Some birds use UV light, which the researchers didn't analyze, to find their prey. But for most of the hungry lizards and crabs patrolling Guam, the blennies should blend right in to the rocks.

To find out how well this camouflage really protects leaping blennies, Morgans and Ord set up 70 fake fish as bait. They molded plasticine blenny bodies with realistic coloration and anchored them to spots around the island with fishing line. Some fake blennies sat on the rocks, while others were on the sand, where they don't blend in as well.

After three days, Morgans and Ord returned to their fake fish. If the props were nicked, punctured, or had bites taken out of them, the scientists assumed predators had come by. They saw that predators attacked blennies on the sand much more often than those on the rocks.

So their coloration seems to be crucial to the leaping blennies' survival on shore. The scientists think that in this regard, the fish may have just been lucky. When they compared the Pacific leaping blenny to 12 closely related blenny species, they found that all the relatives have similar coloration. (Some of these relatives also spend time out of water, but the Pacific leaping blenny is the only one to live on land full-time.) If the ancestor to all these species had the same rocky skin color, then it was well prepared to wriggle out of the ocean and start a new life on land.

That doesn't mean the transition was easy. Blennies also had to evolve a way to breathe air through their skin, like frogs do. Their tail-jumping trick is helpful too, letting the legless fish propel themselves through their habitat. "Obviously moving about on land is critical," Ord says. (You can watch them leaping in the video below, from his lab's YouTube channel.)

Ord says this freak-show fish actually has a lot to tell us about evolution. For one thing, it demonstrates the kinds of adaptations an animal can make after it transitions to a new home. It also speaks to our own ancestry. "In the late Devonian, fish made the first transition onto land, and from that event evolved all of the land vertebrates we now have in the world," he says. The land fish represent a "snapshot of one of the most important evolutionary events in our history." Our ancestors may have looked equally ridiculous as they floundered on land—but like the leaping blenny, they were going places.




Image: Courtney Morgans, UNSW

Courtney L. Morgans, & Terry J. Ord (2013). Natural selection in novel environments: predation selects for background matching in the body colour of a land fish. Animal Behaviour DOI: 10.1016/j.anbehav.2013.09.027

Turtle Moms Choose Their Babies' Genders by Where They Build Their Nests

If turtles had realtors, their motto would also be "Location, location, location!"—but not because they care about a scenic vista. The spot a mother turtle chooses to dig her nest determines whether her young will be males or females. This might even be the most important factor in her decision.

A female painted turtle (Chrysemys picta) is not an over-involved parent. She digs a hole in the dirt, lays a batch of eggs there, and buries them. Then she returns to her freshwater life without giving the nest another thought. The eggs incubate and develop under the soil while the summer wears on. Hatchlings finally chip their way free in the late summer or early fall, but in cooler parts of North America they don't leave the nest right away; they stay hunkered down with their siblings to hibernate until the following spring.

Sometime in the middle of the summer, a significant event happens inside each buried egg: the developing turtle becomes male or female. Its sex hasn't been determined by its genes like ours is. Instead, as with many other reptiles, the temperature in the nest tilts the egg toward one sex or the other. Cooler nests produce males and warmer ones make females. If the nest stays within a narrow temperature range, hatchlings of both sexes will crawl out at the end of the season.

Timothy Mitchell, a Ph.D. student in ecology at Iowa State University, studies a population of painted turtles living in northwestern Illinois. These particular turtles have been under close watch by scientists for more than two decades, but it hasn't become clear whether turtle moms are active in determining their hatchlings' sex—do they choose nest sites that will best balance the sex ratio of their eggs? To find out, Mitchell set up a kind of nest-building competition between himself and the mother reptiles.

Mitchell scoped out 20 nests in his study site, a forested area near the Mississippi River. Right after the mothers left their nests behind, he went in and dug the eggs up. Then he tucked the eggs into artificial, Styrofoam-box nests. Half the eggs from each batch went into a box right next to where their mother had left them, buried at the same depth to create a controlled replica of the original nest. The other half went into a box at a site Mitchell selected at random.

(How do you randomly place a turtle nest? Mitchell used a random number generator to choose a distance away from the original nest, up to 30 meters. Then he flung a pencil in the air and walked in whatever direction in was pointing when it fell. If the resulting location was, say, in the Mississippi, he tried again.)

Just before they were due to hatch, the eggs were dug up and brought to a lab. Mitchell monitored their hatching and then returned the tiny turtles to their artificial nests for hibernation (along with a sprinkling of eggshells, as if the turtles had been there the whole time). He checked on the baby turtles once more in the spring.

Temperature sensors hidden in the nests revealed that sites chosen by turtle moms were a little warmer than Mitchell's randomly selected ones. This meant they were more open to the sun; nests that were shaded by vegetation were cooler.

Between the original nest sites and the random ones, there was no difference in the number of eggs that survived all the way through hatching and hibernation. But there was a major difference in sex ratio: while the turtle moms' nest sites produced roughly equal numbers of boy and girl turtles, the hatchlings from Mitchell's randomly placed nests were about 80 percent male.

"This strongly suggests this process of sex ratio selection is influencing where Mom chooses to nest," Mitchell says, "as opposed to selection to have eggs survive."

Wherever she builds her nest within this forest, a painted turtle mother can be assured that her young will survive equally well. But it's in her best interest to keep the sex ratio balanced. In the long term, turtles that tend to build male-heavy or female-heavy nests will lose out when the population swings in that direction, because young turtles of the opposite sex will then have better mating prospects.

A warming climate is a threat to any species whose sex ratios depend on the temperature. But if female turtles are savvy enough to leave their eggs in exactly the right sex-balancing spot, should we stop worrying about them? "That is still the big question in the field!" Mitchell says. He thinks moms' choice of nest sites will be a crucial part of how this species responds to climate change. But many other factors will matter too, like the fragmentation of the turtles' habitat and how the climate affects their predators. Turtle moms today know how to build a perfect nest for their offspring , but that balance may be as fragile as eggshells.


Image: Timothy Mitchell.

Timothy S. Mitchell, Jessica A. Maciel, & Fredric J. Janzen (2013). Does sex-ratio selection influence nest-site choice in a reptile with temperature-dependent sex determination? Proceedings of the Royal Society B DOI: 10.1098/rspb.2013.2460

Fungus-Farming Beetles Start Tending Their Crop as Babies

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

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

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

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

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

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

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

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


Image: Toki et al.

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

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

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

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

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

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

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

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

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

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

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

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

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

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


Image: by Krajten (via Wikimedia Commons)

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

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

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

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

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

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

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

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

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

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

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

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


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

Image: McCullough & Emlen.

To Crash Others' Nests, Cuckoos Impersonate Birds of Prey

In the avian world, cuckoos are the villains you root for. These diabolical birds can trick others into raising the cuckoos' young instead of their own. From a thick playbook of deceptions, one trick cuckoos use is to impersonate local bullies. This apparently convinces their victims to let cuckoos walk right into their nests.

Cuckoos live all over the world, and most species are model citizens, building their own nests and raising their own offspring. But many species are so-called brood parasites, which sneak their eggs into other birds' nests. Some species match the egg's color to their host's eggs to disguise it, while others don't bother, depending how clever their preferred targets are. In certain species, male cuckoos goad the host parents into chasing them off while females creep into the nest and lay their eggs.

The parasitic cuckoo hatches earlier than the other eggs in its nest and gets a head start in begging the host parent for food. It may mimic the appearance of its nestmates. Often, it kicks them out of the nest altogether. The clueless host parent feeds and raises the young cuckoo until it can fly off on its own.

Obviously, it's in the best interest of host birds to keep cuckoos out of their nests in the first place. Parasitic cuckoos and their host species engage in a constant evolutionary arms race, with the parasite's tricks and the host's defenses always improving. Thanh-Lan Gluckman, a Ph.D. student at the University of Cambridge, and her advisor, Nicholas Mundy, studied one of these tricks: plumage that disguises cuckoos as birds of prey.

It's no secret that certain cuckoos resemble certain raptors, and vice versa. The hawk in the photo above (left) is named the African cuckoo-hawk because of the likeness. Gluckman and Mundy wanted to measure that likeness: How similar is the plumage of raptors and cuckoos? And is that similarity stronger in species that live in the same area, suggesting the cuckoos have evolved to mimic specific birds?

The researchers focused on the chest feathers, where many cuckoo species have a "barred" pattern that's similar to many raptors'. It makes sense that the cuckoo's front side would be disguised, rather than its back, because that's what a host bird sees as a cuckoo swoops toward its nest. (And the last thing it sees before its young are replaced with aliens.)

Using museum samples, the authors photographed the plumage of representative birds. Then they transformed the images digitally to represent how they'd look through a bird's eyes. Characteristics of the barred pattern—how big the markings are, how consistent or variable the pattern is, and so on—were compared between five Old World cuckoo species (each representing a different genus) and raptors that share their territory.

All five cuckoos had patterns that matched a local raptor, such as a hawk or buzzard that overlapped with their territory. But when the scientists compared pairs that didn't live in the same area, there was no match. This suggests that cuckoos don't just imitate raptors in general; instead, they've evolved to match specific birds that live around them.

If the raptor it's imitating is local, that means the cuckoo's intended victim—the bird whose nest it's about to invade—will recognize it too. Gluckman says the purpose might be frightening host birds so they don't attack, "or making them misjudge what the cuckoo is for long enough to access the nests." A cuckoo can toss its host's eggs from the nest and lay its own in just ten seconds, she says. Alternately, males that are imitating a dangerous raptor might convince host birds to chase after them, also buying the female time to sneak into the nest.

It will take more research to show exactly how host birds react to an approaching cuckoo disguised as a bird of prey. Probably how they should react is to just move underground, because nothing else seems to be working.


Images: Left, African cuckoo-hawk by Ken Clifton; right, Oriental cuckoo by Tom Tarrant (both via Flickr).

Thanh-Lan Gluckman, & Nicholas I. Mundy (2013). Cuckoos in raptors' clothing: barred plumage illuminates a fundamental principle of Batesian mimicry. Animal Behaviour DOI: 10.1016/j.anbehav.2013.09.020

Fish Evolve Stabbier Genitals When Predators Are Near

Like sock garters and homburg hats, the equipment used by our great-grandparents doesn't always cut it for later generations. Certain male fish have evolved differently shaped genitals depending on what other fish share their caves. Attracting females, though, doesn't seem to be as important as not getting eaten.

Most fish reproduce simply by scattering a lot of of eggs and sperm around their environment. But a few types of fish are "livebearers": their eggs are fertilized and hatched inside the female's body, then come swimming out as fully formed miniature fish. Many sharks bear live young. So does Gambusia hubbsi, the Bahamas mosquitofish.

The main difficulty of reproducing this way—at least, the main difficulty from a male perspective—is getting the sperm inside the female's body. You can't just leave it around the ocean and hope for the best. Males in the mosquitofish's family solve this problem with an organ called a gonopodium. The body part's overall size is subject to a couple of different evolutionary pressures: Females of some species prefer a larger gonopodium. But carrying around the bigger organ slows males down when they're trying to escape predators.

Justa Heinen-Kay and R. Brian Langerhans at North Carolina State University were curious about just one part of the gonopodium. The tip is tiny but weapon-like: about one millimeter long, it carries bony hooks, spines, and teeth. It's not big enough slow males down while swimming, or visible enough for females to judge it. Yet the authors wondered whether other evolutionary pressures might be acting on this spiky little body part.

The researchers collected mosquitofish from water-filled, vertical caves in the Bahamas called blue holes. Certain populations of mosquitofish live in caves that also contain their predator Gobiomorus dormitor, the bigmouth sleeper. Other populations live with few predators, and can swim and mate—a process that may or may not involve female cooperation—without the threat of being eaten.

Comparing mosquitofish from 10 caves with predatory bigmouth sleepers and 12 caves without them, Heinen-Kay and Langerhans saw that the fish had evolved different genital shapes. Male mosquitofish that lived with a lot of predators had longer tips on their gonopodia, and those tips were more densely covered in bony bits.

This sturdier, stabbier tip may help a male to work more quickly and efficiently, whether or not the female wants him to. The authors speculate that when predators are nearby and time is short, this genital shape is an advantage. Bony hooks "may serve as holdfast devices," and a longer shape might get sperm farther inside the female while pushing out anything competitors have left behind. But in caves without predators, they add delicately, "males may rely more on cooperation and less on genital shape."

However it helps, modifying the shape of their genitals must be a powerful tool for mosquitofish. Over and over again, fish populations living with predators have evolved in the same way. It's a trend that's here to stay—despite what their ancestors might think.


J. L. HEINEN-KAY, & R. B. LANGERHANS (2013). Predation-associated divergence of male genital morphology in a livebearing fish. Journal of Evolutionary Biology DOI: 10.1111/jeb.12229

Image: Heinen-Kay and Langerhans.

Mice Mark Their Territory with Song

Like warring street-corner troubadours, certain mice sing to claim their territory. They may not get any tips in their guitar cases, but by knowing where it's safe to sing, they keep the whole neighborhood harmonious.

Two related species of singing mice share the mountains of Costa Rica and Panama. One, Scotinomys teguina or Alston's singing mouse, lives at lower altitudes and is widespread in the forests of Central America. The other species, Scotinomys xerampelinus or the Chiriquí singing mouse, resides on the tops of the mountains. Males of both mice make chirping calls, unique to their species, that attract mates and advertise to competitors.

But the two tuneful rodents don't exactly meet up for karaoke duets. Bret Pasch, a biologist at the University of Texas at Austin, investigated three mountains where a clear boundary line divides the territory of Alston's mice below from Chiriquí mice above. Why, he asked, is this division so sharp?

Using traps baited with peanut butter and oats, Pasch and his colleagues first documented where the boundary between mouse species was. Then they set up face-offs between males of the two species. Placing pairs of trapped mice in enclosures together, they saw that S. xerampelinus, the higher-altitude mouse, was more aggressive and tended to attack the lower-altitude species. (The lower-altitude mouse is probably wise to retreat, since it's a smaller animal.)

Returning to spots on the mountainside where they knew each species lived, the researchers broadcast recordings of both kinds of mice singing, and listened for responses. Chiriquí singing mice, the more aggressive species, responded to calls of either kind. But Alston's singing mice were more likely to hush up when they heard a song from their rivals. When a male Alston's singing mouse was by itself in an enclosure, the sound of the other mouse's song—played from a speaker—was enough to make it retreat to a far wall and stay there.

Pasch concluded that the higher-altitude mice aren't intimidated by their neighbors, but are restricted to the mountaintops by temperature. The lower-altitude mice, wary of encounters with their larger and more aggressive upstairs neighbors, stay away whenever they hear that mouse's song. When Pasch removed all the Chiriquí mice from certain boundary-zone areas (by trapping them and then carrying them across a river), he saw that Alston's mice quickly moved into the vacant territory.

Alston's singing mice use their relatives' song as a hint to stay away, and Pasch says this sort of interaction could be widespread. "Closely related species often share similar ecological requirements—eating similar foods and living in similar places—as well as similar means of communication," he says. Because of this, communication between species "is probably common." Just don't expect them to appear together in concert.


Image: Alston's singing mouse, by Bret Pasch.

Bret Pasch, Benjamin M. Bolker, & Steven M. Phelps (2013). Interspecific Dominance Via Vocal Interactions Mediates Altitudinal Zonation in Neotropical Singing Mice. The American Naturalist DOI: 10.1086/673263

Coloring In Birds' Bellies with Magic Marker Makes Them Healthier

Remember when you were a kid and the magic marker boxes always had some sort of really elaborate drawing on the back? As if to say, "Buy these eight wide-tip Mr. Sketches and you, too, will be able to create a photorealistic portrait of a scarlet macaw"? But when you bought the markers and tried to copy the picture, it always came out as a stupid magic marker bird? You might have gotten more realistic results by coloring directly on a real animal. Some scientists tried this, and changed the birds' entire quality of life.

In North American barn swallows (Hirundo rustica erythrogaster), males and females with darker-tinted bellies are able to have more young. But they don't get their tan tummies by lying in a UV bed. The birds develop their color months before the breeding season starts, and it depends on both genetics and their health at the time.

Biologists call dark bellies on barn swallows an "ornament," like long tails or showy sets of antlers in other species. These traits may not serve a practical purpose, but they can advertise to potential mates how healthy or hardy the animal lugging that long tail around is.

Ecologist Maren Vitousek at the University of Colorado, Boulder, and her colleagues wanted to know whether barn swallows' ornamental belly feathers could also work in the other direction. A bird's health or fitness affects the color of the feathers—but can the color of the feathers also affect the bird's health?

The researchers captured 60 female barn swallows in Colorado, shortly before the time of year when the birds would be pairing off with mates. Using marker, they colored in the entire belly area of half the birds. The shade—PrismaColor light walnut no. 3507—was within the natural range of hues for barn swallows. Then the scientists sent the newly made-over birds back out into the world.

About a week later, the scientists began to recapture the birds. (They found 36 out of the original 60.) Ordinary, uncolored birds had higher levels of oxidative damage in their blood than when they were first captured. Their bodies had been under stress. But birds with darkened feathers actually had less oxidative damage than before.

Vitousek, who's now at Cornell University, thinks coloring in female birds' belly feathers made their lives easier. "Darker plumage may signal social status in barn swallows," as it does in some similar birds, she says. If so, other birds may have judged their tanned peers to be of higher status, and possibly more likely to win a fight. "As a result, they may be challenged less," she says.

Even though birds or other animals sometimes develop their showy traits well before the mating season, this kind of feedback loop would let these traits remain honest signals of how healthy an animal is. Fitter birds make darker feathers, and darker feathers seem to keep birds healthier by sparing them harassment. "What we are finding is that the appearance of an individual alone can also influence physiological state—and probably fitness—by changing social interactions," Vitousek says.

And all it takes to change a bird's social status is a quick pass with magic marker. Maybe it can be a post-retirement hobby for that Mr. Sketch package artist.


Maren N. Vitousek, Rosemary A. Stewart, & Rebecca J. Safran (2013). Female plumage colour influences seasonal oxidative damage and testosterone profiles in a songbird. Biology Letters DOI: 10.1098/rsbl.2013.0539

Image: by Walter Siegmund (via Wikimedia Commons)

This post has been submitted to the 2013 blog contest held by the National Evolutionary Synthesis Center (NESCent).

Farmer Slime Molds Carry Pest-Killing Friends to Protect Their Crop

Even single-celled farmers have to protect their crop from hungry mouths. That's why slime molds carry certain toxic bacteria inside their bodies on their way to farming others in the soil. Like living Roundup, these bacteria harm competitors while helping their farmer hosts to survive and even thrive.

Slime molds start out life as one-celled amoebae, living in soil or mulch and munching their way through the bacteria there. Once food becomes scarce, they seek each other out and glom together into big, gooey colonies. Some species form blobs that are big enough to see with your naked eye as they ooze across a forest floor in search of greener pastures. Individuals in the blob may use their bodies to build stalks, lifting other individuals as spores. These travelers will be carried away by the wind to start over someplace new.

Dictyostelium discoideum amoebae, when they set out into the world as spores, don't go unprepared. Debra Brock, a PhD student at Rice University at the time, announced in 2011 that some slime molds are farmers. Before the last of the food runs out, they tuck a few edible bacteria into their bodies. Then they launch themselves into the wind, and when they land they seed the soil with the crop they've been carrying.

Brock found that about a third of wild Dictyostelium discoideum slime molds are farmers. But if this is true, how do they deal with moochers? Farmers pay a price for their pastime—they have to set aside the last bit of available bacteria instead of eating it. If their neighboring amoebae can eat all the food they want, then live off the bacteria crop that farmers plant in a new location, why aren't farmers at a major disadvantage?

Brock, who's now a research scientist at Washington University in St. Louis, may have found the answer by digging deeper into the pockets of the amoebae. Farmers don't only carry food with them when they disperse, she saw: they also carry inedible bacteria. Once everyone makes their way to a new plot of land, could these bacteria somehow be protecting their hosts from moochers?

To find out, she mixed farmers and non-farmers together in dishes with plenty of food bacteria—and added a little sprinkle of the inedible pocket bacteria. Farmers stayed perfectly healthy. But non-farmers suffered, producing only half as many spores as usual.

Next Brock spun down samples of the inedible bacteria to extract a liquid from them, which would contain any chemicals the bacteria give off. When she gave doses of this liquid to both farmer and non-farmer amoebae, the non-farmers suffered again. Not only were the farmers fine, but they actually benefited, producing more spores than when they were dosed with a control liquid.

Finally, farmers and non-farmers were grown together and allowed to compete, along with a few species of bacteria that the farmers had carried with them. The more farmers there were, the worse non-farmers fared.

The Dictyostelium discoideum individuals that opt for a farming lifestyle seem to keep deadbeats away by bringing other bacteria with them. Brock doesn't know what weapon these bacteria give off that's bad for non-farmers. But she speculates that the system may have evolved because certain slime molds were genetically predisposed to gather up bacteria before traveling. These farmers would have been likely to vacuum up toxic bacteria along with the edible ones. By developing a resistance to the toxin—and even a way to benefit from it—the slime molds found a way to make farming profitable.


Image: Dictyostelium aggregation, by Bruno in Columbus (via Wikimedia Commons)

Debra A. Brock, Silven Read, Alona Bozhchenko, David C. Queller, & Joan E. Strassmann (2013). Social amoeba farmers carry defensive symbionts to protect and privatize their crops. Nature Communications DOI: 10.1038/ncomms3385

Fish Grow Big Fake Eyes When Predators Are Near

If you're a young, edible animal, a little flexibility about how you develop can save your behind. Or, if you're a damselfish, it can get a few bites taken out of your behind but ultimately save your life.

The damselfish Pomacentrus amboinensis lives on coral reefs in the western Pacific, where it spends its days nibbling algae and trying to avoid being swallowed. As juveniles, these small fish have a pronounced eyespot toward the back of their bodies—a cartoonish false eye drawn on the body, like you might see on a butterfly's wing. Normally, the eyespot fades as the fish matures.

Researchers from James Cook University in Australia and the University of Saskatchewan in Canada asked just how flexible damselfish are while those false eyes are fading away. Can fish opt to keep their false eyes in certain situations? And if they do, does this not-very-subtle disguise actually do anything to protect them?

The scientists raised damselfish in tanks divided into compartments. Some damselfish lived alongside a natural predator of theirs: Pseudochromis fuscus, the "dusky dottyback." Thanks to the special tanks' clear windows and shared water, the young damselfish could see and smell the predator all the time. Other damselfish were raised on their own, or in tanks shared with a harmless vegetarian fish.

After maturing for six weeks in their respective tanks, the fish showed some clear differences. Compared to the other fish, damselfish that had lived near predators had larger false eyes. And their real eyes—startlingly to the scientists—were actually smaller.

"I was very surprised by the result," says lead author Oona Lonnstedt, a PhD student at James Cook University. "It just goes to show the lengths small prey will go to minimize predator attention on their front end."

This assumes that the point of all this camouflaging—growing a big fake eye near your tail and minimizing the actual eyes on your face—is to focus predators' attention on the wrong end of your body. The researchers didn't test predatory fish to see which part of a damselfish they chomped down on. But they did put the damselfish from their experiment onto isolated reef patches in the wild to see how they fared.

Within two days, up to half of the control fish (those raised alone or with non-predators) had disappeared from the reefs, and were presumed eaten. Damselfish that had grown up in a tank with predators, though, radically outperformed the others. Four days after being released onto the reefs, 90% of them were still alive and well.

Their large eyespots and minimized eyes may have made predators chase their back end, where a bite isn't as fatal as one to the head. These fish had also grown up taller in the spine-to-belly dimension, which gives an added challenge to hunters limited by the size of their mouths (and may give the damselfish better bursts of speed too). In the lab, these fish were less active and spent more time hiding; their reticence may also have helped them survive in the wild.

There's a trade-off happening, Lonnstedt says. Damselfish that live with predators and grow large false eyes also have stunted eye growth, which probably impairs their vision. It's not bad enough, though, to keep them from avoiding predators on the reef. In the end, being flexible about how their bodies develop allows them to survive and swim another day.

Image: Lonnstedt et al. (The fish on top grew up in the predator tank.)

Lönnstedt OM, McCormick MI, & Chivers DP (2013). Predator-induced changes in the growth of eyes and false eyespots. Scientific reports, 3 PMID: 23887772

Multitaskers Make the Best Lovers, Say Tree Frogs

It's not an impossible demand. It's just that a male tree frog can choose to spend his energy doing one thing or another thing, and females prefer that he does more of both. The best multitasker might be allowed to fertilize her eggs.

"The males gather in ponds in the evening and begin to call," says University of Minnesota ecologist Jessica Ward, setting the scene. The species in question is called Cope's gray tree frog. Next, she says, females come to the pond and spend a few minutes listening to nearby males. Then they choose for mates the ones whose calls they find most attractive.

What's attractive? There are a couple of ways a Cope's gray tree frog can make his song stand out from others in a chorus. The frogs can increase the speed of their calls, making more trills per minute. Or they might make each one of those trills last longer.

Ward and her colleagues set out to test whether male frogs can only devote energy to one of these factors at a time. And, they asked, are females more attracted to "multitaskers" who can manage both at once?

By haunting parks in the middle of the night with recording equipment, the researchers captured a thousand total calls from 50 different frogs. They found that males who called more often made shorter calls, and those who called less often made longer calls. In other words, there's a trade-off: when a frog puts more energy into one aspect of his song, he has to skimp elsewhere.

Next, the researchers interrupted male and female frogs that were already clasped together to do the deed and carried them back to the lab. The females were put into sound chambers, where they heard two different male frog songs at a time and could choose one to approach. The artificially generated songs had varying call lengths and speeds. Female frogs, it turned out, preferred the songs that had the best combination of long and frequent calls: the more male effort a song would have required, the more a female liked it.

Male frogs, meanwhile, were put into a kind of competition. They sat in a sound chamber and trilled away first on their own, then while hearing the sound of other frogs singing. Males adjusted their own songs when their neighbors were singing at the same time, making each call longer. But they also called less frequently, so the total amount of effort they put into each call stayed the same.

Males may already be expending almost all the effort they can to sing, Wade says. She thinks males who can make their calls faster and longer at the same time are somehow more fit than others. A study in a related species showed that frogs who put more effort into their calls were better swimmers, for example. So females may be onto something when they choose the male with the most difficult song to father their eggs.

This type of multitasking, where a tradeoff exists between different aspects of an animal's performance, has also been studied in birds. Wade says this is the first multitasking study in frogs. Though it's tempting to imagine humans caught in our own version of this trap—asked to attend to an impossible number of factors at once to be maximally attractive—Wade thinks of a different species next. "The multitasking hypothesis may also apply to some spiders," she says.


Image: Cope's gray treefrog by Geoff Gallice (via Flickr)

Jessica L. Ward, Elliot K. Love, Alejandro Vélez, Nathan P. Buerkle, Lisa R. O'Bryan, & Mark A. Bee (2013). Multitasking males and multiplicative females: dynamic signalling and receiver preferences in Cope's grey treefrog Animal Behaviour, 86 (2), 231-243 DOI: 10.1016/j.anbehav.2013.05.016

What's the Point of Making This Face When We're Scared?

If cartoonists ever pause in their sketching to ponder human evolution, they must feel grateful to the forces that shaped our fear expression. All it takes is a pair of extra-wide eyes to show that a character is freaking out. There may be a point to this expression beyond making artists' lives easier: widening our eyes expands our peripheral vision, and might even help other people spot the cause of our alarm.

"Our lab is interested in the evolutionary origins of emotional expressions," says Daniel Lee, a graduate student in psychology at the University of Toronto—in other words, "why they look the way they do." When we feel afraid, for example, is there a point to stretching out our eyelids and raising our eyebrows to the ceiling?

To explore this question, Lee and his coauthors first asked whether widening our eyes helps us see better. They had 28 volunteers look at a fixed spot on a computer screen while holding their eyes in a neutral expression, an expression of fear, or one of disgust. (Subjects acted out these expressions rather than, say, having a chair pulled out from under them before each trial. Lee points out that emotions themselves may also change our perception, but he wanted to study the effects of widened eyes separate from any psychological effects of fear on the brain. "We coached each participant on how to make fear and disgust expressions based on the Facial Action Coding System," he says.)

Subjects were tested with flashing images on the screen in their peripheral vision. Lee found that people making a disgusted expression—with the eyelids narrowed as in "Ew, get that out of my face"—scored the worst. People making a wide-eyed fear expression scored the best, with a useful field of vision 9% larger than that of people with a neutral expression.

Being afraid, then, may help us gather more visual information about whatever's threatening us in our environment. But does it also help us communicate that threat to our companions?

The researchers next used pictures of models' eyes expressing different emotions to create simplified, graphic eye images. (They didn't use real eyes because those might have conveyed extra emotional information, instead of only varying in wideness.) Subjects saw these eye images flash briefly on a screen, looking toward the right or left by varying degrees. Lee found that when the eyes were wider, subjects had an easier time telling which way they were looking. The results are reported in Psychological Science.

"We believe the widening eyes of fear...[are] a functional response for vigilance toward threat," Lee says. When we're scared, he thinks, widening our eyes helps us to see threats and to communicate their location to our group.

The researchers point out that human eyes are uniquely suited for this kind of communication: we're the only primate with a white sclera (the area outside the iris). In other apes and monkeys, this part of the eye is dark. It's yet another factor that cartoonists, no doubt, appreciate.


Lee, D., Susskind, J., & Anderson, A. (2013). Social Transmission of the Sensory Benefits of Eye Widening in Fear Expressions Psychological Science DOI: 10.1177/0956797612464500

Image: by Tom Check (via Flickr)

Tone-Deaf Birds Disrupt Society, Are Easier to Get into Bed

While male birds are singing elaborate arias and flashing their feathers, it's easy to imagine their female counterparts are unimportant actors. Duller and quieter, all a lady bird has to do is hold still and let one of these frantic performers mate with her. Yet in brown-headed cowbirds, at least, the quiet female keeps the whole society in order. Scientists discovered this by targeting a tiny portion of the female brain and frying it.

Males of the species Molothrus ater use their songs to compete with each other and to woo females. Once a a mating pair forms, they stay faithful to each other for the whole mating season, the male guarding his partner from rivals.

Near the top of the bird brain, a region called nucleus HVC controls females' choosiness toward their potential mates. Scientists at the University of Pennsylvania and Wilfrid Laurier University performed brain surgery on female cowbirds, carefully destroying only this region. Then they put their lobotomized females back into the dating arena to see what would happen.

First, the ladies listened to recordings of male songs. The researchers played tunes sung by a variety of males and observed the females' responses. (When they like what they hear, female cowbirds show it by crouching down in a copulation-ready pose.)

Normal females were choosy, only responding to the highest-quality male songs. Females who'd had brain surgery, though, responded positively to every song.

The researchers wanted to see what effect the females' new, lax attitude would have in cowbird society. So they put post-surgery females, normal females, and males in one big group together. Then they watched.

At first, it looked like nothing was different. Females missing their HVC seemed to act the same as females with intact brains; once they were all together in the aviary, there was no clear difference in how often females approached male birds or in how they "chattered" back at males to encourage their singing.

Nevertheless, something had changed. The other birds in the aviary treated post-surgery females differently. For one thing, females missing their HVC were serenaded by a greater variety of males, even once they'd chosen a mate. Normally, a female who's bonded with a male hears his song almost exclusively. This is a measure of how strong the bond between partners is, says study author David White. Now, with more males bending a female's ear, her pair bond was weaker.

There were other changes too. With the altered females introduced into the group, female birds competed more for mates. And the whole hierarchy of male birds, which is established before the breeding season starts, was disrupted. Male cowbirds sing at each other to show who's dominant. After the HVC-less females came to live with them, the rules about which males were dominant singers shifted significantly.

"The result in this paper turned everything around for us," White says.

Previously, it had seemed to be the male cowbird's responsibility to create a strong bond with his partner. Females appeared to be passive agents in the group. "They don't sing, they don't fight," White says. "They don't, to our eye, do much of anything." Yet when the choosiness was erased from females' brains, the whole group dynamic changed. "Now we could see that it was the female that was playing a much more active role in pair-bonding, and in all sorts of other roles within the social network," White says. Everything depended on her song preferences.

Incidentally, it's not clear why female cowbirds bond with males at all.

Females have likely evolved to pick mates whose songs demonstrate—somehow—that they have the best genes. Then the males keep singing to the females throughout the breeding season, strengthening the bond between them.

Usually, White says, bird couples only form strong bonds when both parents will need to care for the young. But cowbirds "are very bad parents overall" who abandon their eggs in the nests of other birds. The powerful bond between cowbird partners "really makes no sense," White says.

Yet once they're bonded, males direct almost all their singing to their partner and never try to mate with other birds. "They follow each other around, they eat together, he comes when she calls him," White says. If a female dies or disappears, he adds, "her pairmate just becomes a wreck. We call it the widowed male phenomenon."

After the loss of his mate, the male gives up for the season. "He flies around looking for her," White says. To him, at least, the quiet female never seemed unimportant.


Maguire, S., Schmidt, M., & White, D. (2013). Social Brains in Context: Lesions Targeted to the Song Control System in Female Cowbirds Affect Their Social Network PLoS ONE, 8 (5) DOI: 10.1371/journal.pone.0063239

Image: female brown-headed cowbird by JanetandPhil (via Flickr)

Scientists Unsure Why Female Flies Expel Sperm and Eat It

She's apparently a picky mater but not a picky eater. The female of a certain fly species, after mating with a male, dumps his ejaculate back out of her body and onto the ground. Then she gobbles it up. Despite new hints that this behavior may help the female choose which partner fertilizes her eggs, or keep her healthy in times of famine, scientists are still a little perplexed by it.

Various female insects, spiders, and birds are known to expel the male ejaculate from their bodies after the deed is done. In some cases, it seems to let them decide which male's sperm reaches their eggs. Females don't always choose who mates with them, but that doesn't mean they have no choice in their progeny's fatherhood. (This kind of female choosiness about sperm can lead to evolutionary arms races between males and females. The "copulatory plug" is a popular tool among male insects, spiders, reptiles, and even some mammals.)

Eating the ejaculate, as Euxesta bilimeki does, is less popular. This fly lives on agave plants and mates pretty much all the time. "Females can be observed escaping male advances in chases that can last more than an hour," write Christian Luis Rodriguez-Enriquez and his coauthors from the Instituto de Ecología in Veracruz, Mexico. Using videocameras and careful meal planning, they tried to divine a reason for the female flies' behavior.

Out of 74 females that the researchers recorded mating, every one expelled and ate the ejaculate afterward. The researchers then killed the females and pulled them apart with tweezers to look for sperm inside their various storage locations. They found that three-quarters of the females had kept some sperm from their male partner, while one-quarter had expelled it all.

There was no obvious rule to which sperm the females kept. There were some patterns, though. For example, females that mated with larger males, then waited longer before expelling the sperm, were more likely to keep some. Since the female's behavior doesn't seem random—and since it's possible for her to keep no sperm at all—the authors think she may be choosing between mates after the fact.

This could explain why the female expels the sperm, but not why she eats it. In another experiment, researchers fed female flies various diets and measured whether supplementing those diets with ejaculate made them healthier. When female flies were starved entirely, the extra snack did help them live longer—but under normal circumstances there was no difference. The authors report their results in Behavioral Ecology and Sociobiology.

"Our study appears to have raised more questions than provided answers," the authors admit. They expected there would be some clear nutritional benefit to justify the females' tastes.

Rodriguez-Enriquez and his coauthors speculate that the ejaculate-as-meal habit may have evolved as a "nuptial gift." This is an edible present that male insects sometimes give to females as part of their courtship. Usually it's nutritious—a nicely wrapped dead bug, say—but in some cases it's just an empty sac. The ejaculate may be, like these gifts, just an edible empty gesture.

(The above is a video of Euxesta bilimeki flies mating. It doesn't look any different from what you're imagining, but the soundtrack is a nice twist.)

Rodriguez-Enriquez, C., Tadeo, E., & Rull, J. (2013). Elucidating the function of ejaculate expulsion and consumption after copulation by female Euxesta bilimeki Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-013-1518-5

Image and video: Rodriguez-Enriquez et al.

Why Fish Raise Foster Kids (and Give Up Their Own)

A fish swims along a sandy lake bottom, carrying one of its babies in its mouth. It approaches the nesting cave of another family of fish. With a furtive "ptooey," it leaves the baby behind for adoption. For certain fish, this seems to be a common scene: giving up your young and taking on others' may be the best way to ensure your offspring grow past snack size.

The fish in question is Neolamprologus caudopunctatus, a type of cichlid (pronounced like a compliment for someone's hat).* Just a couple of inches long, the diminutive fish lives only in East Africa's Lake Tanganyika. Males and females form monogamous pairs. They raise their young in burrows under rocks; carrying sand in their mouths, they pile it up around the rocks to build narrow entrances.

For the first 40 days or so in the lives of the young fish (called fry), both parents work to protect them from predators. They guard the nest and attack any other fish that come by looking for a meal. Cichlids can also protect their young by carrying them inside their mouths.

As the fry grow older and start swimming on their own, they may wander away from their parents' nests and into nearby ones. However, cichlids have also been spotted carrying young in their mouths and leaving them at other nests. Scientists at the Konrad Lorenz Institute of Ethology in Vienna set out to see how much of the baby swapping among N. caudopunctatus is intentional.

Researchers scuba dived down to the home of the cichlids, mapped the locations of their nests, and collected DNA samples. Back on land, like the crew of a daytime talk show for African lake bottoms, they analyzed the DNA to find out just how these fish were related.

Out of 32 nests, more than half held adopted fry, the authors report in Behavioral Ecology. Within nests that housed adopted fish, those outsiders made up anywhere from 10% to 77% of the nest.

The researchers took their DNA analysis a step further for a dozen adopted fry, hunting down their biological parents. They found that while some fry had been adopted from nearby nests, others were a very long way from home—as far as 40 meters or more. "It is virtually inconceivable that they swam there alone," says senior author Richard Wagner. The lake is packed with hungry predators. It would be, he says, "like a toddler walking across a busy city without mishap." It's more likely that parents deliberately carried these young fish in their mouths from one nest to the other.

There was another piece of evidence that adoptions happened on purpose. Adopted fish were on average larger (which is to say older) than non-adopted fish across the whole sample. But within each nest, the size difference wasn't significant. This suggests that when cichlid parents give up their young, they select nests with fry that are close in size to their own. Such a strategy might make the adopted fish less conspicuous to predators.

Parents who leave their fry at other nests may be hedging their bets, making sure that at least some of their offspring survive if their own nest is wiped out by a predator. As for adoptive parents, they could just kick out the freeloading fry. But keeping adopted fish around means that when predators attack, there's a smaller chance of your own offspring ending up in another fish's mouth.

"Our paper adds evidence that adoption is an adaptive strategy," Wagner says, rather than simply the result of wandering babies. We humans aren't the only animals that regularly choose to raise others' young. One hopes, though, that human foster parents aren't in it for the reduced predation.


Schaedelin, F., van Dongen, W., & Wagner, R. (2012). Nonrandom brood mixing suggests adoption in a colonial cichlid Behavioral Ecology, 24 (2), 540-546 DOI: 10.1093/beheco/ars195

Image: N. caudopunctatus by Varmer (via Flickr)

*"Sick lid!"

NOTE: It's been pointed out to me by an astute reader (my mother) that the hat compliment could also be "chic lid." Fair point, Mom. 

The Composer and the Cassowary: An Appreciation of Mistakes

High in a church balcony last weekend, waiting to perform a solo for Palm Sunday and trying not to panic, I thought about cars being hit with hammers. I'm not sure this is the kind of visualization recommended for singers. But sometimes genetics asserts itself.

A college biology professor once told my class that genetic mutation is like whacking a car with a hammer. You will almost never improve your car this way. More often, you'll damage it. If you're lucky the damage will be only superficial: a change in the silent portion of your genome, or maybe a few funny feathers.

The piece my choir was getting ready to sing, Gregorio Allegri's Miserere, has experienced some mutations in its own DNA over the centuries. Allegri composed the piece way back in the early 1600s, and after that it was sung exclusively during Holy Week at the Sistine Chapel. Even though people had to attend a 3 AM service in Rome to hear it, the Miserere became famous. The Vatican, wanting to keep the piece to itself, threatened excommunication for anyone who copied down the score.

As secrets and life forms tend to do, though, the music leaked out. In the late 18th century, a certain precocious teenager with the last name of Mozart spent Holy Week in Rome with his father. After hearing the Miserere at the Sistine Chapel, young Wolfgang sat down and transcribed the whole thing from memory. He returned for a second performance to double-check his work. From there, the score got into the hands of a music historian who published it.

If the music had really been genetic material, Mozart would have been DNA polymerase, a molecular machine that copies DNA. The polymerase molecule grasps a DNA strand and crawls along, letter by letter, building a matching strand as it goes.

Like Mozart, the enzyme is good at what it does. It proofreads. But sometimes it slips up: A single letter of DNA might be swapped for another one. A section of the code might be flipped backward. One or more letters might be inserted or deleted. (Even one letter lost or gained can cause a major change, since the DNA code is read in three-letter words. In English, imagine losing a letter from the sentence "SHE ATE THE RED BUG" and ending up with "SEA TET HER EDB UG." Some words are still there, but the meaning of the sentence is destroyed.)

Even if DNA polymerase is performing well, damage to the genome can come from outside sources such as UV radiation. But a large fraction of your DNA seems to do nothing at all. If a mutation happens here, you won't know the difference. If a slip-up creates a synonymous change in a gene—the code allows for some words to be spelled in multiple ways—you'll also be fine. And if the mutation does something horrible, it will remove you from the gene pool.

Evolution doesn't care much about any of this. It only notices the rare constructive strokes of the hammer, and it only sees them if they happen in the cells that will become your sperm and eggs (called the "germ line"). If you have DNA damage in the skin of your back from too much tanning, you can't pass it on to your children.

Back when Allegri's Miserere was being sung in the Sistine Chapel, the choirs were made up of men and boys. In choirs like mine, women sing the alto and soprano parts. But that's only a superficial mutation; we singers are the flesh of the piece.

The germ line mutation came in the 19th century. Someone who copied the piece apparently made a mistake, shifting a whole repeated section up by a fourth. What started out as a normal soprano solo now rocketed all the way to a high C, a preposterous note that humans are almost never asked to sing.*

Natural selection didn't weed out this mutation. Once the change had happened and been passed to new generations of the musical score, it stayed in place—even after the error was discovered. We continue to sing the mutated piece because, simply, it's awesome this way. Here's a video. You'll know when the boy soprano hits the high C: it's the note you hear through the bones of your spine instead of your ears.

It's not an overstatement to say that what happened to Allegri's music represents the whole history of life on Earth. Every new development has come from a mistake, small or egregious, that was allowed to stick around for one reason or another. Life started as tiny blobs, then whoops—heads! Legs! Oops again—tulips! Uncorrected errors became tree bark, snail shells, lungs, fur, resistance to antibiotics. Inching along mistake by mistake, life forms developed the machinery to make blood, slime, deadly venom, and spider silk.

Some living things have come together so elegantly that they bring an audience to its feet. There are racing cheetahs, swooping owls, orchids that mimic bees. But even the giant, gut-colored flower that stinks like a corpse to attract flies is a success in its family line. The cassowary is a bird that made so many mistakes, it traded the ability to fly for tree-trunk legs and a head with a sail on top. Even the cassowary, though, is doing something right. Errors become the high notes.

Postscript: My choir director turns out to have a son who, at age three, actually took a hammer to the family car while it was in the garage. The car was not improved. 

Images: Top, cassowary from The New Student's Reference Work and Gregorio Allegri, both via Wikimedia Commons. Bottom, cassowary by Peter Nijenhuis via Flickr.

*Plot clarification, in case anybody is worrying about me up there in the loft: this is not the part I sang.