The cooperative, semi-suicidal blob lurking beneath the cow pasture

Aggregating Dictyostelium discoideum; photo from a series available at Wikimedia Commons

Amoebae gone to pasture

Timeline, 2009: Lurking beneath the soil and cow patties of a southeast Texas cow pasture, the cellular slime mold cloned itself and cloned itself again until it was about 40 feet across, billions of cells dense. The thing is, this enormous creature was really neither a slime nor a mold, but a group of social microbes, amoebas that were all exactly identical to one another.

It’s a cell, it’s a colony, it’s…a multicellular organism!

No one is quite sure why some microbes are social. But the cellular slime mold, Dictyostelium discoideum, makes a great model for figuring out why. This organism, a eukaryote, can start out life as a single cell, one that hangs out waiting for a hapless bacterium to wander by so it can have dinner. But if bacteria are in short supply or the soil dries up, slime molds can do some marvelous things. They can start socializing with each other, forming colonies—apparently quite large colonies. But they also can shift from being single-celled organisms or single-celled colonial organisms to becoming a multicellular organism. In the really bad times, these cells can signal to one another to differentiate into two different tissues, officially becoming multicellular.

In addition, these brainless blobs also exhibit altruism, a kind known as suicidal altruism in which some cells in a colony commit cell suicide so that cells elsewhere in the colony can thrive. And as the discovery in the Texas cow pasture shows, the organisms can exist in enormous clonal colonies, a quivering gelatinous mass just under the soil, waiting for conditions to improve.

An affinity for dung

How did the researchers even find this slime mold? They had to get themselves into the “mind” of the slime mold and figure out where this species might be most prone to going clonal, a response to an uninviting environment. Given that slime molds are fond of deep, humid forests, the researchers opted to search for the clonal variety in a dry-ish, open pasture at the edge of such forests. Why would they even expect D. discoideum to be there? Because the amoebae also happen to have an affinity for dung, as well as soil.

After careful sampling from 18 local fields, which involved inserting straws into cow patties and surrounding soil, the research team tested their samples for the presence of amoebae. Once the dishes showed evidence of the slime mold, the investigators then sampled each group and sequenced the genome. That’s when they realized that 40 feet of one cow pasture was one solid mass of amoebae clones.

The winner clones it all?

These findings raise intriguing questions for microbial ecologists. One problem they’re tackling is what determines which clone gets to reproduce so wildly at the edges of acceptable amoeba territory. Is it just one clone that arrives and gets to work, or do several show up, have a competition, and the winner clones all? They tested this idea in the lab and found that none of the clones they tested seemed to have any particular competitive advantage, so the selection process for which amoeba gets to clone at the edges remains a mystery.

Another question that intrigues the ecologists is why these single-celled organisms cooperate with one another in the first place. Such clonal existence is not unknown in nature—aspen trees do it, and so do sea anemones. And researchers have identified as many as 100 genes that seem to be associated with cooperative behavior in the slime mold. One explanation for cooperating even to the extreme of individual suicide is the clonal nature of the colony: the more identical the genes, the more the species derives from sacrificing for other members of the species. They ensure that the same genes survive, just in a different individual.

Machiavellian amoebae: cheaters among the altruists

Not all amoebae are altruistic, and some apparently can be quite Machiavellian. Some individual amoeba carry cooperation genes that have undergone mutations, leading them to be the cheaters among the altruists and take advantage of the altruistic suicide to further their own survival. What remains unclear is why cooperation continues to be the advantageous route, while the mutant cheats keep getting winnowed out.

Amoebae gone to pasture

By Emily Willingham

Word count: 672

 

Lurking beneath the soil and cow patties of a southeast Texas cow pasture, the cellular slime mold cloned itself and cloned itself again until it was about 40 feet across, billions of cells dense. The thing is, this enormous creature was really neither a slime nor a mold, but a group of social microbes, amoebas that were all exactly identical to one another.

No one is quite sure why some microbes are social. But the cellular slime mold, Dictyostelium discoideum, makes a great model for figuring out why. This organism, a eukaryote, can start out life as a single cell, one that hangs out waiting for a hapless bacterium to wander by so it can have dinner. But if bacteria are in short supply or the soil dries up, slime molds can do some marvelous things. They can start socializing with each other, forming colonies—apparently quite large colonies. But they also can shift from being single-celled organisms or single-celled colonial organisms to becoming a multicellular organism. In the really bad times, these cells can signal to one another to differentiate into two different tissues, officially becoming multicellular.

In addition, these brainless blobs also exhibit altruism, a kind known as suicidal altruism in which some cells in a colony commit cell suicide so that cells elsewhere in the colony can thrive. And as the discovery in the Texas cow pasture shows, the organisms can exist in enormous clonal colonies, a quivering gelatinous mass just under the soil, waiting for conditions to improve.

How did the researchers even find this slime mold? They had to get themselves into the “mind” of the slime mold and figure out where this species might be most prone to going clonal, a response to an uninviting environment. Given that slime molds are fond of deep, humid forests, the researchers opted to search for the clonal variety in a dry-ish, open pasture at the edge of such forests. Why would they even expect D. discoideum to be there? Because the amoebae also happen to have an affinity for dung, as well as soil.

After careful sampling from 18 local fields, which involved inserting straws into cow patties and surrounding soil, the research team tested their samples for the presence of amoebae. Once the dishes showed evidence of the slime mold, the investigators then sampled each group and sequenced the genome. That’s when they realized that 40 feet of one cow pasture was one solid mass of amoebae clones.

These findings raise intriguing questions for microbial ecologists. One problem they’re tackling is what determines which clone gets to reproduce so wildly at the edges of acceptable amoeba territory. Is it just one clone that arrives and gets to work, or do several show up, have a competition, and the winner clones all? They tested this idea in the lab and found that none of the clones they tested seemed to have any particular competitive advantage, so the selection process for which amoeba gets to clone at the edges remains a mystery.

Another question that intrigues the ecologists is why these single-celled organisms cooperate with one another in the first place. Such clonal existence is not unknown in nature—aspen trees do it, and so do sea anemones. And researchers have identified as many as 100 genes that seem to be associated with cooperative behavior in the slime mold. One explanation for cooperating even to the extreme of individual suicide is the clonal nature of the colony: the more identical the genes, the more the species derives from sacrificing for other members of the species. They ensure that the same genes survive, just in a different individual.

Not all amoebae are altruistic, and some apparently can be quite Machiavellian. Some individual amoeba carry cooperation genes that have undergone mutations, leading them to be the cheaters among the altruists and take advantage of the altruistic suicide to further their own survival. What remains unclear is why cooperation continues to be the advantageous route, while the mutant cheats keep getting winnowed out.

Your mother *is* always with you

Mother and child, microchimeras

When you’re in utero, you’re protected from the outside world, connected to it only via the placenta, which is supposed to keep you and your mother separated. Separation is generally a good thing because you are foreign to your mother, and she is foreign to you. In spite of the generally good defenses, however, a little bit of you and a little bit of her cross the barrier. Scientists have recently found that when that happens, you often end up toting a bit of mom around for decades, maybe for life.

The presence of cells from someone else in another individual is called microchimerism. A chimera in mythology was a beast consisting of the parts of many animals, including lion, goat, and snake. In genetics, a chimera carries the genes of some other individual along with its own, perhaps even the genes of another species. In microchimerism, we carry a few cells from someone else around with us. Most women who have been pregnant have not only their own cells but some cells from their offspring, as well. I’m probably carrying around cells from each of my children.

Risks and benefits of sharing

Microchimerism can be useful but also carries risks. Researchers have identified maternal cells in the hearts of infants who died from infantile lupus and determined that the babies had died from heart block, partially from these maternal cells that had differentiated into excess heart muscle. On the other hand, in children with type 1 diabetes, maternal cells found in the pancreatic islets appear to be responding to damage and working to fix it.

The same good/bad outcomes exist for mothers who carry cells from their children. There has long been an association between past pregnancy and a reduced risk of breast cancer, but why has been unclear. Researchers studying microchimerism in women who had been pregnant found that those without breast cancer had fetal microchimerism at a rate three times that of women who with the cancer.

Microchimerism and autoimmunity

Autoimmune diseases develop when the body attacks itself, and several researchers have turned to microchimerism as one mechanism for this process. One fact that led them to investigate fetal microchimerism is the heavily female bias in autoimmune illness, suggesting a female-based event, like pregnancy. On the one hand, pregnancy appears to reduce the effects of rheumatoid arthritis, an autoimmune disorder affecting the joints and connective tissues. On the other hand, women who have been pregnant are more likely to develop an autoimmune disorder of the skin and organs called scleroderma (“hard skin”) that involves excess collagen deposition. There is also a suspected association between microchimerism and pre-eclampsia, a condition in pregnancy that can lead to dangerously high blood pressure and other complications that threaten the lives of mother and baby.

Human leukocyte antigen (HLA)

The autoimmune response may be based on a similarity between mother and child of HLA, immune-related proteins encoded on chromosome 6. This similarity may play a role in the immune imbalances that lead to autoimmune diseases; possibly because the HLAs of the mother and child are so similar, the body clicks out of balance with a possible HLA excess. If they were more different, the mother’s immune system might simply attack and destroy fetal HLAs, but with the strong similarity, fetal HLAs may be like an unexpected guest that behaves like one of the family.

Understanding the links between microchimerism and disease is the initial step in exploiting that knowledge for therapies or preventative approaches. Researchers have already used this information to predict the development of a complication in stem cell transplant called “graft-versus-host disease” (GVH). In stem cell transplants, female donors with previous pregnancies are more associated with development of GVH because they are microchimeric. Researchers have exploited this fact to try to predict whether or not there will be an early rejection of a transplant in kidney and pancreas organ transplants.

(Photo courtesy of Wikimedia Commons and photographer Ferdinand Reus).

Pitcher plant port-a-potty for the tree shrew

A pitcher plant (courtesy of Wikimedia Commons)

Timeline, 2009: As humans, we are a bit limited in our imaginations. For example, we’d probably never consider climbing onto the edge of a toilet seat and licking the sides while…um…employing the toilet for standard uses. Perhaps one reason—among many obvious choices—is that we’re not tree shrews living in the wilds of Borneo in Southeast Asia.

If you’re now envisioning tree-dwelling rodents enjoying the civilized development of having their own toilet, you’re not too far off. Borneo is home to a number of unusual relationships between species, but none may be stranger than the one that has developed between the tree shrew and the pitcher plant. The pitcher plant is carnivorous, and as its name implies, has a pitcher-shaped structure that it uses to trap its food.

The many uses of the pitcher plant

Normally, a pitcher plant growing on the ground is the perfect trap for hapless animals drawn to its minimal nectar output. For some species, they’re not a death trap but a place to brood offspring—one frog uses the pitcher plant to lay its eggs, where trapped, digested insects may provide some nourishment. The insects fall in because the funnel-shaped pitcher part of the plant has a slippery lip that acts as a deadly superslide for any insect that alights on it. Unable to gain a foothold, the animal slides helplessly into the plant’s interior, landing in a pool of digestive enzymes or bacteria that slowly break it down.

What does a pitcher plant do with digested insect? It does what any organism, plant or otherwise, does with its food—it extracts nutrients from it. One primary nutrient that plants (and everything else) require is nitrogen. This element is part of life’s important building blocks for DNA and RNA and the amino acids that make up proteins. Thus, to grow and reproduce, organisms must acquire nitrogen from somewhere. Some plants form a partnership with bacteria to get their nitrogen. Pitcher plants digest insects for it.

Unless no insects are available. While ground-growing pitcher plants in Borneo can subsist on available ants and other crawly critters, some pitcher plants grow on vines and trees, where ants are largely unavailable. In addition, mountainous environments are not known for harboring lots of ants, so the pitcher plant needed a new plan for getting its nutrients.

Nectar for nitrogen

The plan, it seems, was selection for making more nectar, reducing the slippery factor, and behaving like both a toilet and a food source for an abundant animal in the Borneo mountains, the mountain tree shrew. Using video cameras, researchers based at a Borneo field station captured one of the most unusual mutually beneficial relationships in nature: the tree shrew, while enjoying the abundant nectar uniquely produced by these aerial pitcher plants, also poops into the pitcher plant mid-meal. The plant, perfectly shaped for the tree shrew to park its rear just so while it eats, takes up the feces and extracts nitrogen from it. In fact, these pitcher plants may derive up to 100 percent of their nitrogen from the tree shrew poop.

Researchers think that this friendly relationship must have been in the making for a very long time. The pitcher plant opening is perfectly shaped and oriented so that the nectar collects just at the lip and the shrew must orient while eating so that the funnel-like pitcher collects any poop that emerges. The plant also has developed sturdier and thicker structures that can support the weight of a dining/excreting tree shrew, which isn’t much at less than half a pound, but quite a bit for a plant to support.

As odd as this adaptation may seem, it’s not unique. Ground-dwelling pitcher plants have formed similar mutually beneficial relationships with insect larvae that help themselves to some of the insect pickings that fall in. These larvae excrete any leftovers, and the plant harvests nutrients from these excretions. Interestingly, the tree shrew itself dines on insects, so the pitcher plant is still indirectly deriving its nitrogen from insects even when it uses tree shrew poop. It’s just getting it from the tail end of a rodent intermediary instead.

Water bears go where no animal has gone before

A water bear (OMG, they're so cool!)

Timeline, 2008: They say that in space, no one can hear you scream (or at least that Alien movie said it). The reason for that is that sound waves require matter to be propagated, and in the vacuum of space, there is no matter. Hard as your vocal cords may push, they can’t make the sound travel through nothing.

That vacuum carries other complications for people beyond an inability to chat unprotected. Space is cold—temperatures run close to absolute zero, or -272 Celsius. With the vacuum, there is no oxygen and no pressure. And let’s not forget the bombardment with deadly cosmic rays and, if you’re hanging around just above Earth, UV rays 1000 times more powerful than those we experience on terra firma.

Boiling saliva and bubbling blood. Ewww.

Thus, if you send person or a dog or an ape unprotected into space, within minutes, the lack of pressure would lead to an uncomfortable death involving boiling saliva and bubbling blood. Yet, there are organisms known to survive the environment of space, primarily some bacteria and lichen, the symbiotic combination of algae and fungus. Now, we’ve learned that a little critter that lives on lichen also can be quite the intrepid space traveler.

Water bears–not even remotely like bears

The space animals—the first animals, in fact, known to pull off unprotected space travel—are representatives of two species of tardigrades. There are up to 1000 species of these little animals, more familiarly known as “water bears” because of their rotund, bear-like appearance. Researchers had noted their hardiness under earthbound conditions, observing that although the animals thrive in a damp environment, when conditions go dry, they can shut down for as long as 10 years until the environment moistens up again. Some accounts have compared the water bears to “Sea Monkeys,” the brine shrimp of comics advertisements that come to you dried up in a little packet, only to “miraculously” come to life when you add water.

On a September 2007 European Space Agency mission, scientists decided to test the tardigrades in the most hostile environment available—in space just above planet Earth. They tested two species of water bear, Richtersius coronifer and Milnesium tardigradum, both entering space as dried out versions of their usual selves. The 120 animals from each species were divided into four groups, one that remained on Earth as a control, two that were exposed to the vacuum of space and different combinations of UV rays, and a fourth that experienced only the vacuum of space without the radiation.

Vacuum OK, UV bad

The animals spent 10 days traveling unprotected far above the earth before returning to Earth, where they were hydrated in the lab. Amazingly enough, all three groups of space-traveling tardigrades initially perked right up and lived for a few days. After that, however, only the vacuum-alone group maintained that rate of survival. In the UV-exposed groups, animals that had experienced the vacuum of space and exposure to UV-A and UV-B survived at rates between 10% and 15%. Animals that had been exposed to all three types of UV—A, B, and C—all died.

Nevertheless, the animals that did survive appeared to thrive, reproducing heartily and generally living the usual life of the unusual water bear. Researchers find their ability to withstand radiation particularly intriguing, given that the bombardment would normally shred the DNA of most organisms. Investigators hope to find out more about how the bears  resist the perils of space, seeking perhaps to co-opt some of the tardigrade’s techniques to use in protecting astronauts.

Space, schmace. How about 4000 m deep?

Tardigrades didn’t really need to travel into outer space—or really, inner space—to prove their toughness. They are known to live as high as 6000 meters up in the Himalayas and as deep as 4000 meters down in ocean trenches. Water bears have also been found living in apparent ease in hot springs above boiling temperature.

The narwhal: a serious case of nerves

"Narwhal or unicorn"

Timeline, 2006: The narwhal has a history as striking as the animal itself. Vikings kept the narwhal a secret for centuries even as they peddled its “horn” as that of a unicorn. Narwhal tusks were so prized that monarchs paid the equivalent of the cost of a castle just to have one. They were thought to have magic powers, render poison ineffective, cure all manner of diseases, and foil assassins.

A tooth and nothing but a tooth

As it turns out, the horn is really just a tooth, an extremely long, odd, tooth. The narwhal tusk, which usually grows only on males from their left upper jaw, can reach lengths of six feet or more. Sometimes, males will grow two tusks, one on each side. The tooth turns like a corkscrew as it grows, stick straight, from the narwhal’s head. They are such an odd sight that scientists have been trying to figure out for centuries exactly what that tusk might be doing there.

Some have posited that the narwhal uses the tusks in epic battles with other male narwhals. Others have fancifully suggested that the animal might use the long tooth to break through the ice, ram the sides of ships (nevermind the disconnect between when the tusk arose and when ships entered the scene), or to skewer prey—although no one seems to have addressed how the narwhal would then get the prey to its mouth.

Gentle tusk rubbing

The facts are that the narwhal rarely, if ever, appears to duel with other narwhals. Its primary use of the tusk appears to be for tusking other males, in which the animals gently rub tusks with one another. They also may be used in mating or other activities, although that has not yet been demonstrated. But what has been discovered is that the narwhal ought to be suffering from a severe case of permanent toothache.

Arctic cold strikes a narwhal nerve

Anyone who has ever had exposed nerves around their teeth knows that when cold hits those nerves, the pain usually sends us running for the dentist. Now imagine that your tooth is six feet long, has millions of completely exposed nerve endings, and is constantly plunged in the icy waters of the Arctic. You’ve just imagined being a narwhal.

Dentist on ice

A clinical instructor at the Harvard School of Dental Medicine who thinks of nothing but teeth made this discovery about the narwhal. The instructor, Martin Nweeia, can wax rhapsodic about teeth and how central they are to our health and the stories they can tell even about how we lived and died. He has carried his tooth obsession beyond his own species, however; his passion led him to spend days on Arctic ice floes, watching for the elusive narwhal, or at least one of the tusks, to emerge from the deadly cold water. He also befriended the local Inuit, who rely on the narwhal as a source of food and fuel oil.

His fascination and rapport with the Inuit people ended with his viewing several specimens of narwhal tusks. What he and his colleagues discovered astonished them. The tusks appeared to consist of open tubules that led straight to what appear to be millions of exposed nerve endings. In humans, nerve tubules are never open in healthy teeth. But in the narwhal tusk, which is an incredible example of sexual dimorphism and the only spiral tooth known in nature today, these open tubules were the norm.

Sensory tooth

The researchers speculated that the animals may use this enormous number of naked nerves as a finely sensitive sensory organ. In addition, it is possible that the teeth transmit voltage through a process called the piezo effect, in which crystals generate voltage when a mechanical force rattles them. In the case of the narwhal, who swim quickly through the water, water pressure might provide the force. Because narwhals are among the most vocal of whales, the tusks could also be sound sensors.

Why would dentists be so interested in the tusks of a whale? Examinations of the narwhal tusks have revealed that they are incredibly flexible, unlike our teeth, which are strong but also rigid and comparatively brittle. It is possible that understanding the narwhal tusk might have clinical applications for developing flexible dental materials for restoring pearly whites in people.

Beethoven died of lead poisoning–or did he?

Did lead kill Beethoven?

Timeline, 2005 and 2010: Literary folk have often noted the passion and emotion of Ludwig van Beethoven’s works. Lucy Honeychurch, the heroine of E.M. Forster’s A Room with a View, became “peevish” after playing Beethoven, and of course there’s the famous hooligan Alex from A Clockwork Orange, who was roused to stunning displays of violence after hearing “Ludwig van.” Given Beethoven’s own behavior, which was punctuated by violent rages, frequent sudden outbursts, and wandering the streets humming loudly, it’s not surprising that his music would communicate his passion.

A heavy metal influence?

A study in 2005 (news release here) yielded results that suggested that much of his anger, however, was attributable to the effects of heavy metal…specifically, lead. Beethoven became sick in his 20s (he also went deaf in his 20s), and suffered until his death at the age of 56 from a variety of illnesses, including chronic diarrhea and other stomach ailments. His death was lingering and painful, and some people thought that he had suffered from syphilis. Yet now many of his symptoms fit the classic description of slow lead poisoning. Among the effects of lead poisoning are irritability, aggressive behavior, headaches, and abdominal pain and cramping, all of which Beethoven experienced.

Doctor to businessmen to Sotheby’s to science

Some samples of the great composer’s hair and skull are available today for sophisticated testing for metals. A Viennese doctor apparently snagged a few fragments of his skull 142 years ago and the pieces eventually made their way through the family to a California businessman. The hairs were cut by a student soon after Beethoven died and ended up at a Sotheby’s auction. A few years ago, tests on the hairs suggested that Beethoven’s body harbored high levels of lead—hair accumulates and retains such toxins better than any other tissue—but because the testing method destroyed the hair, further tests were not completed.

Wobbling electrons solve the mystery?

Since that time, a powerful new X-ray technique has become available. The Department of Energy’s Argonne National Laboratory owns the X-ray. In the facility, subatomic particles fly through a tubular tunnel almost at the speed of light, emitting as they travel X-rays 100 times brighter than the sun’s surface. These X-rays can bounce off of the surface of even a tiny sample. As they bounce off of the sample, electrons wobble out of place, releasing energy in a pattern that is specific to the atom being bombarded.

Researchers were interested in Beethoven’s hair and skull pieces. The team that evaluated the samples actually works on developing bacteria that can take up heavy metals and render them relatively harmless; such organisms would be useful in environmental detoxification. They placed Beethoven’s hair in their high-powered X-ray. The electrons wobbled and the pattern indicated that Beethoven was simply full of lead. In fact, they reported that the poor man had about 60 parts per million of lead in his body, which is 100 times normal levels. It certainly was enough to make a person manifest the various symptoms that characterized most of Beethoven’s life.

The team also looked for a pattern that arsenic would emit, and they found none. This result seemed to exonerate Beethoven from having had syphilis, since arsenic would have been the treatment of choice for such an ailment.

Not so fast

At the time the study results were revealed, ideas about how did Beethoven built up so much lead abounded. Some suggested that  his body was less able than normal to rid itself of the heavy metal, through which he’d have been exposed by many channels. His stomach problems and temperament led him to consume much wine, and the vessels for drinking wine contained lead. In addition, his medicines probably were stored in lead-lined bottles or vials, and he may well have visited spas—for his health, ironically—at which he consumed or swam in mineral water containing lead. In one report, Beethoven’s poor doctor was identified as the likely culprit in his demise.

Fast-forward five years to 2010. A deeper analysis (news release here) of the bone fragments from Beethoven’s school indicated that his lead levels were not that spectacular. The bone is the reservoir for most of the lead the body takes up, and Beethoven’s bones simply didn’t have enough to have caused his various physical ailments. While the experts seemed to be in agreement that the results point away from lead, a new heavy metal mystery arose from the results. One skull fragment they tested had about 13 mcg of lead per gram of bone, nothing to write home about, while another sample turned up with 48 micrograms per gram, a much higher level. Nevertheless, we must look elsewhere for what killed one of the world’s greatest western composers. Ideas being tossed around include lupus and heart disease. What we do know is that he lived in terrible pain, both from his maladies and from the treatments designed to help, including pouring hot oil in his ears, according to one Beethoven scholar quoted in the New York Times.

Another wrongly accused suspect

Heavy metals have featured in other historical whodunits. For example, Napoleon reportedly died of stomach cancer during his exile on Elba, but one analysis showed that he actually died of slow arsenic poisoning, suggested to have been at the hand of his closest assistant. Then, much like Beethoven’s story, a later study showed that arsenic likely played no role in the great general’s death.

Nematode may trick birds with berry-bellied ants

Comparison of normal worker ants (top) and ants infected with a nematode. When the ant Cephalotes atratus is infected with a parasitic nematode, its normally black abdomen turns red, resembling the many red berries in the tropical forest canopy. According to researchers, this is a strategy concocted by nematodes to entice birds to eat the normally unpalatable ant and spread the parasite in their droppings. (Credit: Steve Yanoviak/University of Arkansas)

Timeline, 2008: Host-parasite relationships can be some of the most interesting studies in biology. In some cases, a parasite requires more than one host to complete its life cycle, undergoing early development in one host, adult existence in another host, and egg-laying in still another. There’s the hairworm that turns grasshoppers into zombies as part of its life cycle, and the toxoplasma parasite, which may alter the behavior of humans and animals alike. Often, the infection ends with the host engaging in life-threatening behaviors that lead the parasite to the next step in the cycle.

A recent discovery of a most unusual host-parasite relationship, however, results in changes not only in host behavior but also in host appearance. The infected host, an ant living in the forest canopy in Panama and Peru, actually takes on the look of a luscious, ripe fruit.

Berry-butted ants

Researchers had traveled to the Peruvian forest on a quest to learn more about the airborne acrobatics of these ants, Cephalotes atratus. This ant is a true entomological artist, adjusting itself in midair if knocked from its perch. Re-orienting its body, it can glide back to the tree trunk, grabbing on and climbing to where it belongs, avoiding the dangers of the forest floor.

As the investigators monitored the colony, they became aware of some odd-looking members of the group. These ants had large red abdomens that shimmered and glowed and looked for all the world like one of the tropical berries dotting the forest around them. Curious about these odd ants, the scientists took some to the lab for further investigation. Ant researchers are an obsessive breed, and they had even placed a bet over whether or not these berry-bellied ants were a new species.

A belly full of another species’ eggs

When they sliced open one of the bellies under a microscope, what they found surprised them. Inside, a female nematode had packed the ant’s abdomen full of her eggs. The bright red belly was an incubator and, the researchers surmised, a way station on the nematode’s route to the next step in its life cycle. This was the same old C. atratus with a brand new look.

Tropical birds would normally ignore these ants, which are black, bitter, and well defended with a tough, crunchy armor. But any tropical bird would go for a bright, red, beautiful berry just waiting to be plucked. The scientists found that in addition to triggering changes to make the ant belly look like a berry, the nematode also, in the time-honored manner of parasites, altered its host’s behavior: the berry-bellied ants, perched on their trees, would hold their burgeoning abdomens aloft, a typical sign of alarm in ants. A bird would easily be tricked into thinking that the bug was a berry. One quick snap, and that belly full of nematode eggs would be inside the belly of a bird.

Poop: A life cycle completed

And then the eggs would exit the bird the usual way, ending up in the bird’s feces. The ants enter the picture again, this time collecting the feces and their contents as food for their colony’s larvae. The eggs hatch in the larvae and the new nematodes make their way to the ant belly to start the cycle anew.

The nematode itself is a new find, a new species dubbed Myrmeconema neotropicum. And it seems that earlier discoverers of the berry-bellied ants also thought they had a new species on their hands: the researchers turned up a few previous berry-bellied specimens in museums and other collections labeled with new species names. No one had thought that the difference in appearance might be the result of a parasitic infection: this relationship is the first known example of a parasite causing its host to mimic a fruit.

Birds remain the missing link

There is one hitch to the newly discovered nematode-ant-bird association: the researchers never actually saw a tropical bird snap up a juicy, fruit-mimicking ant. They report seeing different species of birds scan the bushes where such ants sheltered, but there were never any witnessed ant consumptions. Thus, this inferred piece of the puzzle—the involvement of birds and their droppings in the life cycle of this nematode—remains to be proven.

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