Tag: mammals

Viruses may explain why small animals are more prone to cancer

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Cancer is a numbers game. Larger, longer-lived animals with more cells should get more tumors than do small, short-lived animals. And yet mice are more susceptible to cancer than we are. Now, a new study offers a tantalizing explanation. The genomes of smaller mammals contain more viruses, which the authors suggest may account for their higher rates of cancer.

Aris Katzourakis, an evolutionary biologist at the University of Oxford in the United Kingdom, didn’t set out to explain rates of cancer in animals. He was interested in why over the last 10 million years the genomes of mice have accumulated 10 times more small RNA viruses, called endogenous retroviruses (ERVs), than has the human genome. He teamed up with researchers from Plymouth University and the University of Glasgow in the United Kingdom to mine for retroviruses in the genomes of a range of mammals—including shrews, humans, dogs, and dolphins. The researchers then tested whether differences in how long mammals live and in how quickly they mature affects how many ERVs they harbor.

By the time the team had identified more than 27,000 unique viral sequences across 38 different mammals, it saw a clear pattern emerging: Small mammals have more ERVs than do larger ones. Mice have more than 3000, whereas dolphins have just 55, and humans are somewhere in the middle with 348, the researchers report online today in PLOS Pathogens.

Larger animals have many more cells, and should therefore have more of these endogenous retroviruses. That they have fewer means they must have found efficient ways to remove them, Katzourakis says. That suggests ERVs can be harmful to their hosts, and this harm is more costly, in an evolutionary sense, to large animals.

How do ERVs harm their hosts? Katzourakis suspects that some ERVs cause cancer. The viruses embed in an organism’s genome and make copies of themselves, and these duplicates then split and reinsert randomly at different locations in the genome. More often than not, these viruses do no harm, but occasionally their reinsertion transforms a healthy cell into a cancerous one. One such event led to the untimely death of the world’s first cloned sheep, Dolly, who succumbed to lung cancer caused by the Jaagsiekte sheep retrovirus. Katzourakis proposes that the higher number of ERVs in small-bodied animals may account for their higher rates of cancer.

“It’s nice to see real experimental results that can help explain the vast differences in cancer susceptibility per gram of tissue between small, short-lived animals and large, long-lived animals,” says epidemiologist Richard Peto of the University of Oxford, who was unconnected to the new study. He first recognized the unexpected differences in cancer susceptibilities between animals of different body sizes in the 1970s, an observation that became known as “Peto’s Paradox.”

From an evolutionary perspective, Peto explains, it makes sense that larger animals are better at protecting their genomes from potentially cancer-causing viruses. Large animals tend to live longer and reproduce later, so it is more important for them to postpone the onset of cancer.

Although the findings pinpoint one mechanism underlying the vast difference in cancer rates, they don’t explain all cancers, says George Kassiotis, a virologist at the National Institute for Medical Research in London who studies ERVs in humans and mice. Despite having few ERVs, he explains, humans still get cancers. ERVs are therefore likely to be one of many factors contributing to cancer rates. “One important aspect of this new study is that it provides a framework to quantify the contribution of ERVs to cancer,” he says, “which in turn will inform the contribution of other causes of cancer.”

Measleslike Virus Likely Culprit in U.S. Dolphin Die-Off

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A measleslike virus appears to be the chief cause of the droves of dead dolphins that have washed ashore along the Eastern Seaboard of the United States this summer, researchers announced yesterday. Since 1 July, 333 bottlenose dolphins have been recovered from beaches between New York and North Carolina—10 times the number usually recovered at this time of year.

In early August, the large number of strandings prompted the National Oceanic and Atmospheric Administration (NOAA) to declare an Unusual Mortality Event. The declaration freed up federal funding to assist NOAA’s Marine Mammal Health and Stranding Response Program to retrieve and assess the mammals’ remains. The results of their investigation point to a type of morbillivirus as the cause of the die-off—a group that includes viruses that cause measles in humans and distemper in dogs.

The team’s detective work combined traditional techniques that examined tissues from dead animals’ lungs, brains, and lymph systems with molecular techniques to probe for the presence of the virus. So far, researchers have examined 33 dolphins; 32 have tested positive for morbillivirus. Genetic sequencing has confirmed that 11 carry the type of morbillivirus that infects only dolphins, porpoises, and whales.

“Along the Atlantic seaboard this [outbreak] is extraordinary; this is the largest outbreak that we have had since the 1987 die-off,” said Teri Rowles, head of NOAA’s Marine Mammal Health and Stranding Response Program, in a teleconference with reporters. Morbillivirus was also responsible for a devastating 1987 die-off which killed more than 700 dolphins.

Many wild dolphins exposed during that epidemic probably developed immunity to the virus, Rowles says. But a population’s immunity is slowly eroded over time; animals born since 1987 are probably susceptible, Rowles says.

The virus may have taken hold when the dolphin population reached a tipping point, with enough susceptible individuals to sustain its spread, says veterinary epidemiologist Stephanie Venn-Watson of the National Marine Mammal Foundation in San Diego, California. The epidemic will continue until the number of susceptible animals dwindles, researchers predict. There is no feasible way to vaccinate or treat the animals, they add.

It is difficult to predict how many bottlenose dolphins will ultimately succumb to the disease, and the documented strandings probably represent just a fraction of the infected animals. It is also not clear whether the virus will spread to other dolphin species. Typically, morbillivirus strains don’t spread beyond closely related species, researchers say.

As for any threat to people, “there is no indication that this virus could jump into humans,” says virologist Jerry Saliki of the University of Georgia in Athens. However, morbilliviruses suppress the immune system, so many of the washed-up animals are sick with secondary bacterial infections that are communicable to other mammals. Under some circumstances, rotting carcasses could pose a threat to beachgoers and other mammals.

NOAA plans to continue to monitor the spread of the infection and investigate whether marine pollution could be worsening the impact of the outbreak. Rowles explains that high levels of polychlorinated biphenyls, or PCBs, known to suppress mammals’ immune systems, have been reported in some areas along the eastern coastline. “We will be monitoring those areas very closely,” she adds.

Permafrost, altruism, and whale dialects

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This week in Science in Action we talked to Ted Schuur, University of Florida, about the impacts of methane-producing bacteria munching their way through thawing poleward soils, Craig Baxter, a UK-playwright, about his award-winning play ‘The Alturists’, and Ian Boyd, University of St Andrews, about an open science project to decode whale song.

You can listen to the programme here or download it here.

Science in Action is hosted by Jon Stewart, produced by me and Ania Lichtarowicz, and is a BBC World Service programme that pulls together the science issues of the week and delivers breaking science news.

Jawbones are ‘shaped by diet’, a study finds

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Diet has shaped human jaw bones; a result that could help explain why many people suffer with overcrowded teeth.

The study has shown that jaws grew shorter and broader as humans took on a more pastoral lifestyle.

Before this, developing mandibles were probably strengthened to give hunter-gatherers greater bite force.

The results were published in the Proceedings of the National Academy of Sciences.

“This is a fascinating study which challenges the common perception that there has been little recent change in the morphology of humans,” said anthropologist Jay Stock from the University of Cambridge.

Many scientists have suggested that the range of skull shapes that exist within our species is the result of exposure to different climates, while others have argued that chance played more of a role in creating the diversity we see in people’s profiles.

The new data, collected from over 300 skulls, across 11 populations, shows that jaws shortened and widened as humans moved from hunting and gathering to a more sedentary way of life.

The link between jaw morphology and diet held true irrespective of where people came from in the world, explained anthropologist Noreen von Cramon-Taubadel from the University of Kent.

Concurrently crooked

It would be tempting to conclude that this is evidence for concurrent evolutionary change – where jaw bones have evolve to be shorter and broader multiple, independent times, she told BBC News.

But the sole author of the paper suggested that the changes in human skulls are more likely driven by the decreasing bite forces required to chew the processed foods eaten once humans switch to growing different types of cereals, milking and herding animals about 10,000 years ago.

“As you are growing up… the amount that you are chewing, and the pressure that your chewing muscles and bone [are] under, will affect the way that the lower jaw is growing,” explained Dr von Cramon-Taubadel.

She thinks that the shorter jaws of farmers meant that they have less space for their teeth relative to hunter-gatherers, whose jaws are longer.

Teeth-pulling tale

“I have had four of my pre-molars pulled and that is the only reason that my teeth fit in my mouth,” said Dr von Cramon-Taubadel.

Ever since that time, she has wondered why so many people suffer with teeth-crowding.

“I think that’s the reason why this result resonates with people,” she said.

Dr Stock added: “[The finding] is particularly important in that it demonstrates that variation that we find in the modern human skeletal system is not solely driven by population history and genetics.”

These results fit with previous evidence of both a reduction in tooth and body size as humans moved to a more pastoral way of life.

It also helps explain why studies of captive primates have shown that animals tend to have more problems with teeth misalignment than wild individuals.

Further evidence comes from experimental studies that show that hyraxes – rotund, short-tailed rabbit-like creatures – have smaller jaws when fed on soft food compared to those fed on their normal diet.

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Primates leapt to social living

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Scientists may be a step closer to understanding the origins of human social behaviour.

An analysis of over 200 primate species by a University of Oxford team suggests that our ancestors gave up their solitary existence when they shifted from being nocturnal creatures to those that are active during the day.

It is likely communal living was adopted to protect against day time predators, the researchers say.

The results are published in Nature.

From work on social insects and birds, some biologists have suggested that social groups begin to form when young do not leave their natal ground, but instead hang around and help raise their siblings.

Now, the latest evidence from primates suggests that this might not have been the case for our ancestors.

Leaping to sociality

By looking at whether closely related species share similar social structures, the Oxford team of evolutionary biologists shows that a common history is important in shaping the way animals behave in a group.

The team pinpointed the shift from non-social to social living to about 52 million years ago; a switch that appears to have happened in one step, and coincided with a move into daylight.

It did coincide with a change in family dynamics or female bonding, which emerged much later at about 16 million years ago.

“If you are a small animal active at night then your best strategy to avoid predation is to be difficult to detect,” explained Oxford’s Suzanne Shultz, who led the study.

“Once you switch to being active during the day, that strategy isn’t very effective, so an alternative strategy to reduce the risk of being eaten is to live in social groups,” she told BBC News.

Dr Shultz thinks that the move to day-time living in ancient primates allowed animals to find food more quickly, communicate better, and travel faster through the forest.

The link between sociality and a switch to daytime living might have been missed until now, she suspects, because biologists interested in this question have tended to work with Old World monkeys, like baboons, which are characterised by female bonded groups, which are not characteristic of many primate species.

Flexibly social

Human societies likely descended from similar large, loosely aggregated creatures, Dr Shultz explained, but the key difference, she pointed out, is that our closest cousins’ societies do not vary within a species, while humans’ do.

“In human societies we have polygyny… we have monogamy, and in some places we have females leaving the group they were born in, and in others males leave,” she said.

Why this difference exist is still unclear.

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Ancient horses’ spotted history reflected in cave art

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Scientists have found evidence that leopard-spotted horses roamed Europe 25,000 years ago alongside humans.

Until now, studies had only recovered the DNA of black and brown coloured coats from fossil specimens.

New genetic evidence suggests “dappled” horses depicted in European cave art were inspired by real life, and are less symbolic than previously thought.

The findings are published in the Proceedings of the National Academy of Sciences.

Horses, which were the most abundant large mammal roaming Eurasia 25,000 years ago, were a key component of early European diets.

So it is not surprising that the cave art of this time had a certain equestrian flair – horses make up 30% of the animals depicted in European cave paintings from this era.

Biologists, interested in the diversity of European animals before the last Ice Age, are interested in how accurately these early artistic impressions portrayed the colouring of the horses that lived alongside the ancient humans.

“It was critical to ensure that the horse depictions from the cave paintings were based on real-life experiences rather than products of the imagination,” explained lead author Arne Ludwig from The Leibniz Institute for Zoo and Wildlife Research in Berlin.

In previous work, Dr Ludwig, and his colleagues, recovered only the DNA of black and brown coat colours from the prehistoric horse bones.

But the dappled coats of the 25,000 year horses depicted at the Pech Merle cave complex in France convinced the team to take a second look.

Fur coats

By revisiting the fossil DNA of 31 horse specimens collected from across Europe, from Siberia to the Iberian Peninsula, the researchers found that six of the animals carried a mutation that causes modern horses to have white and black spots.

Of the remaining 25 specimens, 18 were brown coloured and six were black.

Dr Ludwig explained that all three of the horse colours – black, brown and spotted – depicted in the cave paintings have now been found to exist as real coat-colours in the ancient horse populations.

The researchers say that these three colours probably provided enough variation for humans to create the diversity of coat colours and patterns seen in modern horses.

The domestication of horses, which produced modern breeds, is thought to have begun about 4,600 years ago in the steppe between modern Ukraine and Kazakhstan.

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Pioneers boast high fertility, say scientists

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Scientists have shown that women who were first to settle in a new land had more children and grandchildren than those who followed.

Researchers analysed the family trees of French settlers who colonised Canada in the 17th and 18th centuries.

Their results could help to explain why some rare genetics diseases are common in communities established by migrations.

The findings have been published in the journal Science.

The team of researchers from Canada and Europe relied on data collected by the parish councils of Charlevoix and Saguenay Lac Saint-Jean, a region 170km north of Quebec, Canada.

The towns not only boast dairy farms, charming villages and sandy beaches but some of the best ever-kept marriage records – comprising more than a million people.

By building a picture of marriages and how many children the pairings produced, the researchers showed that woman who arrived as part of the first wave of immigration had 15% more children than those who arrived a generation later.

The pioneering woman married younger and benefited from scooping up the best local resources, they added.

But the study also found that the pioneering women’s children also had more children.

Lead author Laurent Excoffier, from the University of Bern in Switzerland, explained that the children of women at the front of the wave inherited their mother’s higher rate of fertility.

Yet, the researchers added, there was no such correlation between generations that arrived 30 years later behind the first wave.

Dr Excoffier drew parallels with cane toads. Scientists have observed that the toads at the edge of their range have bigger front legs and stronger back legs; all the better to invade new areas.

And when toads at the frontiers breed, their offspring inherit these longer, stronger limbs.

Such an effect is not unexpected, but until now no one has seen this phenomenon in humans.

“This was a rare chance to study a relatively recent human migration,” said co-author Damian Labuda, a geneticist from the University of Montreal, Canada.

Population geneticist Montgomery Slatkin from University of California, who was not involved in the work, called the study one of the “most interesting, detailed studies” he had seen.

“I think what happened [here] could easily have happened in other populations,” he added.

The findings suggest that families at the front of the wave of migration contributed more to the contemporary gene pool than those that were slower to arrive, explained Dr Labuda.

This could help explain why some rare genetic diseases are more common than expected in the Charlevoix and Saguenay Lac Saint-Jean regions.

That is because any disease causing mutations carried by people by the frontiers would be pass onto their descendents, who make up a large proportion of subsequent generations in the population.

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Icelandic rocks could have steered Vikings

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Vikings used rocks from Iceland to navigate the high seas, suggests a new study.

In Norse legends, sunstones are said to have guided seafarers to North America.

Now an international team of scientists report in the journal the Proceedings of the Royal Society Athat the Icelandic spars behave like mythical sunstones and polarise light.

By holding the stones aloft, voyaging Vikings could have used them to find the sun in the sky.

The Vikings were skilled navigators and travelled thousand of kilometres between Northern Europe and North America.

But without a magnetic compass, which was not invented until the 13th Century, they must have relied on other navigational aids.

Without the stars, which would have been out of sight during the constant daylight of the summer months, the sun would have been their best bet to set their course by.

But on cloudy or foggy days the seafarers would have been left with only the direction of the wind and swell to guide their way.

Through the fog

Norse legends tell of seafarers lifting stones to the sky to spy the direction of the sun when it was hidden by cloud cover.

Earlier this year, a study in the Philosophical Transactions of the Royal Society B reviewed the evidence that naturally forming crystals can selectively block light of one polarisation – how waves of light can be restricted to certain directions of oscillation.

The new result shows that Icelandic spars, which are formed from crystallised calcium carbonate, are good polarisers and could have been the raw material of the mythical sunstones.

The spars can be easily cleaved and crafted into a rhombus shape required for the polarising effect, and the discovery of one on the wreck of an Elizabethan ship that sunk in 1592 “looks very promising” the authors report.

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Dolphins ‘decompress like humans’

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Scientists have found tiny bubbles beneath the blubber of dolphins that have beached themselves.

The bubbles were discovered by taking ultrasound scans of the animals within minutes of stranding off Cape Cod, US.

The team’s findings help confirm what many researchers have long suspected: dolphins avoid the bends by taking long, shallow decompression dives after feeding at depth.

The study is reported in Proceedings of the Royal Society B.

Many biologists believe that marine mammals do not struggle, as human divers do, with decompression sickness – “the bends” – when ascending from great depths.

In humans, breathing air at the comparatively high pressures delivered by scuba equipment causes more nitrogen to be absorbed into the blood and the body’s tissues, and this nitrogen comes back out as divers ascend.

If divers ascend too quickly, the dissolved nitrogen forms bubbles in the body, causing decompression sickness.

But marine mammals such as whales, dolphins, and seals are highly adept at dealing with the pressures of the deep.

They slow their hearts, collapse the tiny air-filled chambers in their lungs, and channel blood to essential organs – like the brain – to conserve oxygen, and limit the build-up of nitrogen bubbles in the blood that happens at depth.

However, veterinary scientist Michael Moore from Woods Hole Oceanographic Institute in the US, thinks that it is “naive” to think that diving mammals do not also struggle with these laws of chemistry.

Even marine mammals ascending from the deep must rid themselves of the gas that has built up in their tissues, or risk developing the bends.

If dolphins, he explained, come up too quickly then there is evidence that they “grab another gulp of air and go back down again,” in much the same way a human diver would “re-tank and re-ascend” to try to prevent the bends.

“But there’s one place you can’t do that [if you are a dolphin] and that’s sitting on the beach,” Dr Moore told BBC News.

And so when he and his team scanned eight Atlantic white-sided dolphins and 14 short-beaked common stranded dolphins using ultrasound, they were not surprised to find tiny bubbles below the blubber of the animals.

Because three of the dolphins were scanned within minutes of their stranding, the team ruled out the possibility that the air pockets were a result of beaching, and instead think that they formed while the animals were still in the water.

Bends over

Sascha Hooker, a marine mammal ecologist with the Sea Mammal Research Unit in St Andrews, UK, commented: “This study is much less about why animals strand, and much more about using stranded animals to give us a bit more insight [into] what is going on inside live marine mammals.

“[What’s] particularly interesting from this is that the animals that were released… survived.

“So it looks like these animals are able to deal with some bubbles.”

She explained that studying the behaviour and physiology of diving animals is incredibly difficult because researchers cannot follow them down to the deep.

Stranded animals, therefore, offer researchers rare access to these expert divers to measure what changes they undergo to avoid the bends.

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