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.

Advertisements

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.

Tricky little orchids

Orchids attract collectors all over the world. One of the things that draws us to these unusual plants is their Machiavellian approach to life. They unfeelingly employ deception to their benefit, usually practicing their art on unsuspecting members of the insect community. Research has revealed that one species of orchid, Anacamptis morio (or Orchis morio), or the green-winged orchid, lays its bold insect trap in an attempt to avoid a trap itself.

Inbreeding avoidance: not just for royalty

Although plants can do many things that most members of the animal kingdom cannot—self-fertilize or increase chromosome numbers in a generation—they’re still better off when reproductive measures result in an increase in genetic variation. As with most organisms, inbreeding is not a healthy thing for a plant, and many plants have mechanisms to avoid it.

The idea of inbreeding avoidance led researchers to a theory to explain the remarkable behavior of many orchids. These beautiful, much-coveted flowers attract humans and insects with their alluring fragrances and colors. For insects, some orchids add to the attraction by mimicking the female of the insect species, or wafting the scent of eau d’ dung for insects that prefer laying their eggs in such places. But of the 30,000 known orchid species, about 10,000 have nothing to offer the hapless insect in return: their flowers have no nectar.

Why keep coming back for nothing?

Researchers have sought to explain why insects would continue to visit such a stingy plant, and why the plants continue to get away with and employ their nectar-free strategy. The strategy itself seems in violation of so much of our understanding of the natural world, a place typically characterized by tradeoffs. In fact, orchids without nectar are not wildly popular among insects—it is difficult in many cases to witness a bee pollinating a green-winged orchid in the wild—but they still do manage to get pollinated.

Scientists investigated wild-growing green-winged orchids on a Swedish island and figured out why this species cheats insects so mercilessly. It’s about genetic variation. The flowers attract the bugs, but offer the foraging insects nothing, driving them on to explore other plants. Although the orchids have not provided food, they have given the unsuspecting insect a payload of a different kind: pollen. The bug—still on a quest for nectar—forages in other plants, pollinating as it goes along. Voila! No self-pollination. Plants that result from self-pollination are usually weak and unhealthy, and self-pollinating can be a waste of precious pollen.

Interviewing bees

Scientists detected this self-pollination avoidance by interviewing bees. They queried specific bees with plants that had been artificially dosed with nectar or with plants in their natural nectar-free state. The researchers found that bees stayed around the nectar-ful plants twice as long and investigated twice as many flowers on the same plant, which would promote self-pollination. Bees that found no nectar moved along to other plants, promoting cross-pollination.

One thing that could confound the interpretation of these results is that bees can remember how a plant smells. If a bee strikes out with one orchid, it will remember that orchid’s smell and not waste its time foraging around in other flowers that smell the same.

In separate research performed by a team in Switzerland, scientists found that the flowers of a nectar-producing orchid species all smell very much the same. But flowers on different plants of the green-winged orchid all smell different. A bee might have failure at one green-winged orchid and remember the smell, but then fly straight into another green-winged orchid plant because its smell is different. The unhappy bee falls into the orchid’s trap and gets nothing, but the deceitful orchid itself has had a great success: avoiding the trap of self-pollination.

Crazy cat lady may have microbe to blame

Toxoplasma gondii is the cat-borne parasite responsible for causing toxoplasmosis and a host of other problems in humans. This close relative of the malaria-causing protozoan may drive human behavior and immunity, in addition to causing acute illness and devastating birth defects. Recent research points to a single gene underlying this parasite’s virulence in the human host. It’s scary yet fascinating to think that a single gene from a single organism could have such dramatic effects on our species.

Warning pregnant women away from litter boxes

Because T. gondii infection can result in serious fetal defects, many pregnant women have heard of toxoplasmosis, an illness that often goes unnoticed in the afflicted person. Pregnant women are warned away from cat litter boxes and even away from gardening because contact with cat feces can mean contact with the parasite. T. gondii spends the sexual part of its life cycle in cats, but for its asexual life, it can parasitize a number of hosts, from pigs to lambs to mice to people. People also can acquire the infection from eating undercooked meat or drinking contaminated water. In some countries, like Brazil, up to 60% of the population has been exposed to T. gondii; in the United States, about 33% of people tested have antibodies to the parasite, indicating past infection.

Link between parasite and schizophrenia

The “crazy cat lady” has practically become a social stereotype in the United States and other countries, conjuring the image of a woman who lives with 25 cats and talks to herself a lot. But researchers investigating schizophrenia have actually identified a potential link between people who are exposed to Toxoplasma infection and the manifestations of schizophrenia; for example, several studies have identified higher levels of antibodies to the parasite in people with schizophrenia, and infection with Toxoplasma can cause damage to brain cells that is similar to the damage seen in patients with schizophrenia. Toxoplasmosis can also sometimes lead to symptoms of psychosis.

The fact is that most people don’t know they have toxoplasmosis because they have healthy immune systems. In people with compromised immunity, however, such as those with HIV, T. gondii can precipitate an extreme form of dementia that eventually kills them. The dementia is so severe that the sufferer eventually becomes completely unaware of his or her surroundings and lapses into a coma. The bug, however, also can affect the central nervous system in healthy people and is also linked to severe eye problems even in patients who are not immunocompromised. One researcher has claimed that infection with the parasite makes men dumber and women act like “sex kittens.”

ROP18: Watch out for this one

There are different strains of T. gondii, and investigators have noted that the Type 1 strain is most closely associated with disease. Studies of T. gondii, which has a genome with about 6000 genes, have pinpointed the virulence capacity of the strain to a single gene, dubbed ROP18. This gene encodes a kinase, one of a huge class of cell signaling proteins that add phosphates to molecules. Typically in cell signaling, kinases exist in a series, phosphorylating the next protein in the pathway, which helps maintain regulation of the signaling. The most virulent T. gondii strains have a form of the gene that differs from that carried by benign strains. Researchers speculate that this kinase interferes with a cell’s normal signaling, hijacking it for its own purposes, including growth and reproduction. The good news is that because kinases are so important in cell signaling, pharmaceutical companies have developed libraries of molecules that inhibit specific kinases, so one potential path to preventing toxoplasmosis is to discover an inhibitor of ROP18.

Rats get a little nutty from it, too

Not only has this parasite been linked to the ability to alter human behavior, but it also appears to alter rodent behavior in ways that favor its own reproduction. For example, rodents exposed to toxoplasma via cat feces actually become more likely to hang out near cat urine. If a cat eats the infected animal, the toxoplasmosis bug can then move into the sexual phase of its life cycle in the cat.

Of lice and men

The loneliest Homo

When watching movies about hobbits, dwarves, and elves, I often think that our fascination with other human-like forms comes from our loneliness as a species—we are the sole living representatives of our genus. So we invent other species that might fit into our genus, creating companions for Homo sapiens.

Or…not quite that lonely

New research suggests that in our history we passed enough evenings with other members of our genus to exchange a few parasites—specifically lice—with them. Lice are very host-specific, and requires direct contact to transfer from organism to organism. Host-parasite specificity provides a tool to use the parasite to explore the evolutionary history of the host. This approach is especially handy in situations like the one we face with human evolution: little DNA data from our ancestors, but lots of information about the parasites that colonize us.

Before lice research, we used tapeworms, malaria protozoa, and human papilloma viruses to explore the contours of our family tree. All such studies agree with the fossil and genetic data we have demonstrating our origins in Africa. But the lice tell an even more thorough story with a surprise twist.

A research team that included a high-school student examined the genetics and morphology of the lice that colonize our heads and bodies. What they found was that this louse species—Pediculus humanus—has two lineages, one that colonizes both our heads and our bodies, and another that colonizes only our heads. The head-only louse is found only in the New World (the Americas), while the head-body louse occurs worldwide. The two lineages appeared to have diverged from one another 1.18 million years ago.

As the lice go, so go the Homo

It just so happens that Homo sapiens diverged from Homo erectus about…1.2 million years ago. Head-louse was an H. erectus parasite, and head-body louse was an H. sapiens parasite. When the Homo lineages went their separate ways, the lice co-evolved right along with them and formed two lineages.

They spent about a million years separated, but then something strange happened in the louse lines. They met up again on the same host, turning up on H. sapiens about 25,000 to 30,000 years ago. Head-only eventually made its way to the New World on the heads of H. sapiens.

Reunited…and it feels so…itchy

But how did this meeting of the lice occur? The only way it can: by direct contact between the two hosts. In other words, we found we were not alone. Whether or not we obtained the head-only lice via fighting, mating, or sharing clothing with H. erectus can’t be told. But for awhile there, we had company. Then pretty soon afterward, we didn’t, as H. erectus became extinct.

The lice seem to confirm one of two competing theories about our origins. One idea holds that H. sapiens emerged from Africa, spread around the world, and outcompeted other Homo species. The other theory is that H. sapiens ancestors emerged from Africa, spread around the world, and evolved into Homo sapiens while keeping genes flowing freely among populations. The lice appear to support the “out of Africa” or “replacement” school of thought. The head-body lice underwent the kind of genetic bottleneck that H. sapiens did at the same time in history, possibly because a relatively small group of humans emerged from Africa to find success through the rest of the planet, and took their lice with them.

Look to the pubes?

The research is not complete—there is still the question of how the transfer happened. Turns out, there’s another parasite that might clear up whether or not mating was the method: pubic lice. But we also seem to have a pattern of association with our generic brethren, including H. erectus and H. neanderthalensis: we meet them, and they become extinct. It’s no wonder that we’re alone now.

Death by cat food

Introducing the cane toad:  a very bad decision

Since their introduction into the Australian landscape many decades ago, cane toads have devastated local flora and fauna. The idea was that they would eat the cane beetle, which threatened sugar cane crops. As it turned out, the thousands of introduced toads had little effect on the cane beetle, but they killed or ate just about everything else they came near.

Naturally, ever since then, Australians have tried to find ways to rid themselves of these self-introduced pests, which kill pets, swarm over the landscape in such numbers they look like a moving, toady carpet, and outcompete many Australian natives for food–or, they just eat them.

Cat food lures meat-eating ants

Recent news from Australia was that cane toad hunters might no longer be able to humanely dispatch the amphibians using carbon dioxide gas. Instead, the advice was going to be that bashing them over the head with a single, toad-dispatching blow would be the best way to control them. Now, some Australians have discovered another way to end a toad’s life: Death by meat-eating ant.

Evidently, the ant does not find the toad naturally attractive, but a spoon of cat food near areas where baby toads emerge from ponds brings the ants by the horde. The horde then finds a lot of tasty toads to eat, and…they eat them. Sounds painful, but evidently, it’s pretty effective, and no human has to bash a toad on the head.

The Australian researcher who made the cat food breakthrough is Rick Shine, a noted herpetologist whose recent research on behalf of native herps turned up this low-tech solution to the problem.

Ideas for thinkin’

Introducing the cane toads ended disastrously for Australia. Find other examples of introduced species. Why is it that populations of introduced species seem so easily able to explode in number? Think about concepts of co-evolution and species interactions.

In Austin, Tex., an invasive plant species, Hydrilla, has choked lakes and water treatment plants. Authorities are trying to control Hydrilla by introducing triploid Asian grass carp, another non-native species. What are the grass carp expected to achieve? Why? Why are they triploid? Can you think of benefits of this second introduction? What are some potential drawbacks, and what might be the first sign that they’re in progress? And where did that Hydrilla come from, anyway?

%d bloggers like this: