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.

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Identical twins grow less identical

DNA sequence is just a starting point

Identical twins are identical only in that their DNA is the same. In what might be an argument against cloning yourself or a pet hoping to get an identical reproduction, scientists have found that having an identical genetic code does not translate into being exactly alike. We have long known that identical twins do not always share the same health fate, for example. One twin can have schizophrenia while another twin may never develop it. Or one twin might develop cancer or diabetes, while the other remains disease-free, even though there can be a strong genetic component to all of these disorders.

So a burning question in the field of genetics and disease has been identifying the difference between a twin who gets a disease and one who does not. A strong candidate mechanism has been the process of genomic modification in which molecules attached to the DNA can silence a gene or turn it on. Typically, methyl groups attached to DNA will make the code unavailable, and acetyl groups attached to the histone proteins that support DNA will ensure that the code is used.

Chemical tags modify DNA sequences

This process of genomic regulation is involved in some interesting aspects of biology. For example, methylation is the hallmark of genomic imprinting, in which each set of genes we inherit from our parents comes with its own special pattern of methylation. The way some genetic disorders manifest can be traced to genomic imprinting. In Prader-Willi syndrome, a person inherits a paternal mutant allele and manifests characteristic symptoms of the disorder, which include obesity and intellectual disability. But people who inherit the same mutant allele from the mothers will instead have Angelman’s syndrome, in which they are small and gracile, have a characteristic elfin face, and also have intellectual disability. Modification from methyl or acetyl groups, also called epigenetic modification, plays a role in dosage compensation for the X chromosome. Women, who have two X chromosomes, shut most of one down through methylation to produce an X chromosome gene dosage like that of men, who have a single X.

Twinning: Nature’s clones

Identical twins have identical DNA because they arise from a single fertilized egg. The egg divides mitotically into two identical cells, and then each cell, for reasons we don’t understand well, resets the developmental process to the beginning and develops as a new individual. The process of twinning carries interesting implications for bioethics, cloning discussions, and questions about when life begins, but it also has helped us tease apart the influences of genetics and environment. A recent study examining life history differences and differences in epigenetic modification in 80 pairs of twins ranging in age from 3 to 74 has revealed some fascinating results that have implications for our understanding of nature vs. nurture and our investigations into the role of epigenesis in development of disease.

You are what you do to yourself

The older the twins were, the more differences researchers found in methylation or acetylation of their DNA and histones. For twins raised apart, these differences were even more extreme. Researchers also concluded that environmental influences, such as smoking, diet, and lifestyle, may have contributed to the differences in the twins’ epigenetic modifications. The three-year-old twins were almost identical in their methylation patterns, but for twins older than 28 years, the patterns were significantly different for 60 percent of the pairs.

These results have major implications for our understanding of disease. For example, we can use this knowledge to identify genes that are differently methylated in people with and without a disorder and use that as a lead in identifying the genes involved in that disease state. We also may be able to pinpoint which environmental triggers result in differential methylation and find ways to avoid this mechanism of disease.

A gal for George, the world's loneliest tortoise?

Long-lived, lonely: The tragic fate of Lonesome George

George has seen a lot in his life. He was born sometime between 80 and 200 years ago, so what exactly he’s seen remains speculative. What we do know is that in 1971, some goat herders spotted George on the island of Pinta in the Galapagos, and George’s life changed significantly. Researchers rushed to the site to find the tortoise. The reason for the rush? They thought George was the very last of his subspecies, the lone denizen of Pinta, a survivor of the combined adverse effects of whalers and goats in the Galapagos.

George’s people+goats problem

Probably within George’s memory—if he could form such memories—whalers arrived at the Galapagos islands and decimated tortoise populations by eating the animals, whose abundant meat proved irresistible to the protein-starved mariners. With the people came the goats, and the goats proceeded to eat their way through everything on Pinta that the tortoises like to eat, too, destroying all of the tortoise’s nesting sites in the process. By the 1970s, biologists were pretty sure that there were no longer any Geochelone nigra abingdonii, George’s subspecies, living on the island. Then George popped up his wrinkled head just as the goatherders were walking by.

George elicits some bizarre human behavior, ignores tortoise females

The people took George to a tortoise sanctuary, where they attempted to introduce him to the joys of female companionship. Because George was alone, species-wise, they selected a couple of females from a closely related subspecies, Geochelone nigra becki, who hailed from Wolf Island, part of the Galapagos island chain. There, George lived with the females for 30 years with nary a leering glance at them, much less successful mating. One frustrated researcher went so far as to join George in his pen, where she covered herself in eau d’ female tortoise, excretions from the female that presumably carried male-attracting pheromones. During her time with George, the male tortoise appeared to have a sort of sexual awakening, showing a bit of interest and exhibiting signs of sexual activity. The researcher even confirmed that George was indeed male and that everything appeared to be functioning normally.

Then, her research period at the sanctuary ended, and George lost his trainer in the romantic arts. Bachelor and celibate, his claim to fame remained that he was the world’s loneliest animal. He even made it into the Guinness Book of World Records as the rarest creature on Earth. His sobriquet became Lonesome George, and thousands of people came to view him at his island sanctuary. Over time, he has had his trials: a caretaker who let him eat too much, periodic overindulgence in cactus—a tortoise delicacy—that led to constipation, and a fall that almost killed him. But still, no mating.

Will George find his Ms. Right?

Then, a group of researchers tackled the job of drawing blood from tortoises on the nearby island of Isabela, where a different subspecies of tortoise lives. They performed microsatellite DNA analysis on the blood, a type of analysis that produces a DNA fingerprint that can be used to characterize a species. To their surprise, they found a tortoise among their samples who appeared to be half-George. The male tortoise had a microsatellite DNA pattern that was a 50% match for George, meaning that somewhere on the island of Isabela, a possibly-female G. n. abindonii lurked and, apparently, mated.

Now the search is on for the individual who may blow George’s place in the record books but also be the last hope for their mutual species to persist on the planet. If the tortoise is female, researchers hope to introduce her to George, possibly awakening his long-dormant libido. Meanwhile, George’s former island home of Pinta could be a tortoise Eden for the pair: the goats are gone and much of the vegetation has returned to its original ecological state. If they can find George a mate, he may very well cease to be Lonesome George and become his species’ Adam, partner to the as-yet-unidentified Eve.

Ahem. La-la-la-laaaaaa…squeak

It’s true. They can sing

Male mice can sing. They aren’t exactly sitting underneath an open window on a moonlit night, guitar in hand, crooning an evening serenade to their lady love, but apparently, they do sing for the ladies.

Very few mammals sing. In fact, until the mouse discovery, we and whales were the only verified members of the mammalian choir. Scientists knew that mice vocalize; for example, mice that are surprised or in pain can emit sounds that humans can easily hear, under 30 kHz. Newborn mice can make sounds that their mothers recognize, summoning the dams to make them warm or return them to the nest. And male mice make ultrasonic sounds, above 30 kHz, that the human ear cannot hear. Usually, males make these sounds in response to the smell of an available female.

Birds, mice, whales, people

Because humans and whales make pretty large research animals and ethical issues prevent studies with either, research into how language is learned and how the brain transmits messages about language has relied on birdsong. You may not have thought about it much, but the song a bird sings is really a song, containing repeated melody lines or syllables, and the bird can repeat it given the necessary stimulus. But birds also must learn their songs, and the birds they’re trying to attract must be able to understand them. Because of this requirement for learning, birdsong has been the model for how mammals acquire and learn language.

Birds may be catching a break now, thanks to a recent breakthrough in mouse song. Researchers examined the vocalizations of 45 male mice by placing the mice in a recording chamber. The scientists then inserted through a tube a cotton swab soaked in enough female mouse urine to convince the male to burst into song. After recording the mouse’s vocalization, the researchers manipulated the recordings to so that humans could hear them and then analyzed them using software.

Gus-Gus, is that you?

What they report is that the mice appear to be singing actual songs that contain syllables—very rapidly produced syllables at about 10 per second. In addition, the songs had phrases that the animals would repeat. The mice all seemed to have their own individual songs, and almost all 45 mice sang in response to the urine stimulus.

That mice sing at all was discovered by accident, but the finding that they do sing what appear to be genuine songs opens up a multitude of research possibilities. Among directly related questions to address, scientists must examine how females respond to these calls and whether or not different experiences in fetal development affect the song or success of the song. In addition, scientists must try to demonstrate that the songs are truly learned if the mouse is to be used as a mammalian model for mammalian communication, replacing birdsong.

OK, that’s cute, but why is it relevant?

If the mouse song is learned, the animal will become an important model for these studies. Because mice have been used for decades in genetics studies, there are hundreds of different varieties of mice with genes knocked out or knocked in, and researchers can make their own special strains to assess the effects of a particular gene on song structure or production. We may be able to use this model to identify genes directly involved in learning and communication in mammals.

Identifying these genes could lead to investigations of how developmental processes and differences result in differential learning abilities. For example, people who are autistic exhibit altered communication skills. A stronger understanding of the genetics of mammalian communication may help us to unravel the underpinnings of this aspect of autism and other communication disorders.

These findings also lead to another question that remains to be addressed: Are there other animals that sing a secret song that our ears can’t hear?

Batty bigamy and worse

Normally, inbreeding isn’t such a good thing

The idea that three generations of related females might share the same mate is, frankly, abhorrent and strange to us humans, but among bats, this tactic may be a fairly common phenomenon.

Generally, animals avoid inbreeding with one another because doing so results in the development of “inbreeding depression” in a population. This depression refers to falling rates of reproduction and survival that result when relatives interbreed. An example of what happens with inbreeding can be found among the royal houses of Europe in previous centuries. The members of these families would often receive papal dispensations to ignore the rules about consanguinity—close relatedness—to be allowed to marry another royal personage. There just weren’t that many eligible royal folk wandering around Europe and inbreeding was the ultimate result.

Hidden disorders emerge

Because of this inbreeding, often with third or second cousins marrying through several generations, the royal families would manifest disorders that normally would remain hidden. Some of these disorders required the inheritance of two alleles, both carrying mutations, for them to manifest. If the royal families had not constantly been intermarrying, the two recessive alleles would have been much less likely to come together in a single person. As it was, many royal households had children who were sickly, who could not reproduce successfully, or who manifested mental illness or retardation. One particularly notable trait that arose through several families was the “Hapsburg jaw,” a severe underbite and jutting jawbone that traced its way through the European royal chessboard. One potentate had a jaw deformity so severe that he could not chew his food.

Horseshoe bats don’t care

But the greater horseshoe bat appears to be untroubled by such issues of consanguinity, at least in the sense that related females from several generations will mate with the same male. In the world of the horseshoe bat, it pays to be a male bat who attracts a female. If the male attracts the daughter, he has a good chance of also mating with the mother and the grandmother, too. And he may be set for his relatively long bat-life; greater horseshoe bats can live up to 30 years, and females will consistently select the same male for the annual bat mating ritual, which results in a single offspring per female each year.

In spite of this inbreeding and polygyny, in which several females mate with the same male, the females apparently are quite adept at avoiding mating with their own fathers. A female will only mate with her mother’s partner if her mother has switched partners and is no longer mating with the daughter’s father.

Beat that, Belgium

This complex mating web results in a bat family tree that is more confusing than that of all the royal houses of Europe combined. It is possible for a female bat and her maternal half-aunt to be half-sisters on their father’s side.

How did researchers unravel this remarkable complexity? They identified a colony of female bats—who spend most of the year living in single-sex groups—in an old mansion in Great Britain. DNA analysis showed that the several hundred females lived in about 20 groups of related females who shared mates. The females met up with the males, who lived in a permanent stag party condition in a nearby cave, only once a year. Researchers speculate that females use smell to avoid mating with their fathers.

What benefit this interbreeding?

Why risk interbreeding in the first place? Actually, many species exhibit tactics that lead to closer kinship among individuals. Researchers speculate that closer kinships result in better teamwork to protect the genetic investment. In the world of team-playing ants, for example, female siblings can be 75% related, rather than the 50% most sexually producing species share genetically with their siblings. Experts believe that this extra genetic relatedness enhances the teamwork atmosphere of an ant colony. In much the same way, the related groups of female bats work together to raise the young. Researchers believe that this horseshoe bat tactic may extend beyond the greater horseshoe to other bat species.

Can animals sense disaster?

Animals head for the hills when natural disaster looms

People living and working in national parks where the devastating 2006 tsunami hit made a startling observation within a few days of the disaster. They had found no animal carcasses of any kind. It appeared that animals had somehow managed to avoid the killer waves that resulted in the deaths of tens of thousands of people.

In Yala National Park in Sri Lanka, people flying over the area in helicopters observed horrible devastation—uprooted trees, cars upended, cars in trees—everywhere the waves had roared over the 391-square mile preserve. But one thing they didn’t see were the bodies of dead animals. The park is home to Asian elephants, crocodiles, buffalo, monkeys, and leopards, and every animal appeared to have made for the hills before the waves swamped their habitat.

Some turtle carcasses have washed ashore, but they seem to be the only notable wildlife deaths in the region. At an elephant trekking center in Thailand, two elephants named Poker and Thandung suddenly went nuts, broke their chains, and headed for the hills, carrying four lucky Japanese tourists on their backs. The elephants and the tourists survived the waters that flooded over the area five minutes after the elephants broke free.

A long history of doom-detection

A long, but anecdotal, history of animals’ ability to sense doom underscores the observations from this most recent tragedy. As far back as about 400 B.C., we noted unusual animal activity just preceding a natural disaster. The Greek historian Diodorus observed in 383 B.C. that two days before a destructive earthquake, the rats, snakes, weasels and even worms had decamped from the affected city. Worms—dwelling in the ground and possibly well-equipped with underground sensors—also figured in a mass animal exodus recorded prior to the 1755 earthquake in Lisbon, Portugal, the worst natural disaster on record prior to the recent Asian tsunami.

Dogs bark, geese honk, livestock get bull-headed. In the big Alaskan earthquake of 1964, a rancher could not get his cows to stay in the lowland pastures; the stubborn bovines insisted on grazing in the hills. Later that day, a huge earthquake hit, triggering a tsunami that wiped out coastal Alaskan towns, but the cows survived on their hillsides.

Are humans missing a vital organ?

Animals appear to know something’s coming possibly because they have what one researcher has described as sensory organs to detect tiny changes leading up to a big event. We, unrefined creatures that we are, do not detect these micro-changes and live in ignorance until the disaster hits. But proving that animals have something we don’t in this regard is a bit difficult because we can’t recreate earthquakes or tsunamis in the lab. Sure, we could shake a table or wash water over a false beach, but it’s the signals leading up to the events that we strive to understand. Since we cannot detect them, we don’t know what they are, and we can’t re-create them.

Our only chance of gaining some experimental insight into this phenomenon is to rely, as so many scientists do, on solid preparation for sheer chance. A marine biologist on the U.S. east coast has done just that, and in the process has become the first scientist to acquire actual proof that animals respond to impending disaster.

Sharks reveal a bit of the secret

The biologist, Michelle Heupel, had been radiotagging sharks off the coast of Florida when Tropical Storm Gabrielle approached. Six hours before the storm made landfall, all 14 sharks she was monitoring suddenly evacuated their nursery site. She and others believe that the sharks registered the drop in barometric pressure that preceded the storm. The drop made depths feel shallower, and the sharks instinctively swam en masse for deeper waters. Heupel got another chance to monitor this movement when Hurricane Charley swept onto the east coast. Again, the sharks she was monitoring all rapidly exited the area hours before the storm moved in.

Just eat the broccoli, preferably steamed

A presidential/vegetable debacle

When the first President Bush indicated a distaste for broccoli during his presidency, he set off a firestorm of vegetable-based controversy. Broccoli haters sympathized, but nutritionists were horrified. Turns out, the data are all on the side of the nutritionists.

Research has shown that people who eat cruciferous vegetables—for example, broccoli, cabbage, or cauliflower—have lower rates of cancer. Armed with this information, researchers around the country have sought the cancer-fighting ingredient in broccoli and tried different ways to maximize the benefits we can get from it.

Yes, it’s got healthy stuff in it

They pinpointed the compound of interest in 1992. It is sulforaphane, a phytochemical in a group called the isothiocyanates. These compounds are known to induce apoptosis, or programmed cell death, of cancer cells. Epidemiologists—people who trace and track diseases and their causes—have found lower rates of prostate cancer in men who eat diets high in isothiocyanates. Scientists found that the way we release these cancer-fighting compounds from our veggies is to cut or chew them.

Sulforaphane, one of the most powerful anticarcinogens—anti-cancer compounds—in our food, works through the liver. Our livers are responsible for detoxifying our bodies, which happens in phases. In some cases, liver enzymes can actually turn compounds into carcinogens. But our phase II liver enzymes break down toxins before they can damage our DNA, the molecule that houses our genetic code. Sulforaphane boosts these phase II enzymes, thus wielding its anti-cancer power.

Broccoli pill–or just broccoli?

When the world found out broccoli’s secrets, there was a craze for broccoli-derived supplements that contained sulforaphane. Broccoli-based pills, powders, and teas hit the shelves, and people everywhere crunched into broccoli, possibly wincing like our former president might have as they chewed it up and forced it down. But what they may not have realized is that mature broccoli also has some compounds help liver enzymes that turn compounds into carcinogens. The goal was to find a way to deliver sulforaphane without delivering too much of these less-benign accompaniments, or too much sulforaphane, which can be toxic in large amounts.

One approach was to synthesize a sulforaphane that retained its anti-cancer powers, but was not as toxic in high doses. This compound is called oxomate, and it has been successful in the lab in reducing breast tumors in rats. Another approach was to try to find a broccoli growth stage that made sulforaphane in reasonable amounts, but that did not produce the compounds that elicited the liver’s carcinogen-producing enzymes. Scientists following that line of research discovered that broccoli sprouts, tiny alfalfa-like sprouts grown from broccoli seeds, contain abundant and safe levels of sulforaphane, but do not synthesize the unwelcome compounds that boost carcinogenesis.

When proteins attack

But one thing that food scientists had found was that even when broccoli was consumed, its sulforaphane could be immediately disabled by broccoli protein called the epithiospecifier protein. Sulforaphane in the plant is attached to a sugar via a sulfur bond. When we cut or chew the broccoli, we can activate the enzyme that breaks the sulforaphane off of the sugar. But then there’s that sulfur flapping in the breeze, and the epithiospecifier comes along, yanks off the sulfur, and inactivates the sulforphane. Food researchers have found that cooking broccoli for 10 minutes at 140 degrees Fahrenheit kills off the epithiospecifier protein, leaving behind intact sulforaphane and the enzyme that releases it from the sugar to do its good work in our bodies.

So if you’ve been choking down overcooked broccoli all in the name of health, you may have been reaping the benefits of fiber or other broccoli-derived nutrients, but you weren’t getting much sulforaphane out of it. Your best bet, according to researchers, is to steam fresh broccoli for about three or four minutes and eat it, cheese sauce optional.

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