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).

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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.

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.

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.

Cockroaches are collective food critics

Collective communication guides cockroach dining decisions

Ever drive by a restaurant with an empty parking lot and avoid it yourself because, well, no one else was eating there? If so, you’re not much different from cockroaches. They also appear more attracted to food resources if other cockroaches dine there, as well.

Yes, cockroaches creep me out, too

They’re the only animal about which I’m phobic, but who could resist a story like this? A new study published in Behavioral Ecology and Social Biology has found that cockroaches communicate with each other about preferable food sources, much as people do.  Rather than doing it through visuals of empty parking lots or restaurants or via a critic’s recommendations, however, they probably use pheromones. So, there may be a cockroach pheromone or suite of the chemicals that says, “Hey, this pile of garbage is the best in town!”

The researchers who determined this used a couple of piles of food. The roaches collectively would spend more time and in greater numbers at one pile of food over another. Even more interesting–at least to cockroach researchers–the bugs would linger longer at the dining source if other roaches were there, too. Peer pressure, it appears, is not only a human phenomenon.

It’s not limited only to cockroaches in the insect world, either. There are many other examples of insect chemical communication guiding collective behavior. The most famous is probably the honeybee waggle dance, which the animals use to indicate which way to go to find the best food resources.

Why should we care?

Why would researchers go to the trouble of monitoring cockroach choices over piles of food? One reason is that if we identified the pheromone that communicates “good food pile” to cockroaches, we could use that to lure them into our little pest-control traps. Ever diabolical that way, we humans are. There are some things not even cockroaches can do.

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