New doubt cast on dinosaur-killing asteroid theory

The asteroid blamed for a mass extinction event 65 million years ago could actually predate the demise of dinosaurs by 300,000 years.

By analysing sediments near the asteroid's site of impact, called the Chicxulub crater, researchers have found that the impact did not cause the extinction of any species.

In the Mexican town of El Penon, Princeton University geologist Gerta Keller and her research team found evidence of 52 species in sediments that were deposited both before, and after, the impact.

"We found that not a single species went extinct as a result of the Chicxulub impact," she said.

Keller's report contradicts the popular theory that the Chicxulub impact heralded the extinction of 65 percent of all species, including plants, dinosaurs, and other animals.

She expects her findings to be unsurprising, as no other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction.

Huge amounts of dust and gases from the eruptions could have blocked out sunlight and brought about a significant greenhouse effect, she said.

More information is available from the National Science Foundation's press release.

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'Sex-bias' hormone identified

Scientists have identified a hormone that could be responsible for non-reproductive differences in male and female brains.


The hormone, called Müllerian Inhibiting Substance (MIS), occurs only in men, and has previously been thought to have the sole function of preventing the formation of a uterus.

However, according to a new study of male and female mice, MIS may contribute to sex-linked behavioural traits that the researchers call 'sex-biases'.

"The sex-biases in the body do not define a person's sex or sexuality," explained neurobiologist Ian McLennan, who conducted the research at the University of Otago, New Zealand.

"Empathy, for example, has a female bias, but some of the greatest men are empathetic. Likewise, girls engage in less rough and tumble play than boys, but a boy who shuns rough and tumble play is still a boy," he said.

McLennan and his colleague Kyoko Koishi found most neurons in mice to have an MIS receptor. They then charted the behaviours of particular male and female mice that were missing either the gene for MIS or its receptor.

Male mice missing either of these showed a feminisation of some behavioral traits. The researchers noted differences in the 'male tendency' to explore and spatial processing.

Further work is needed to determine which human traits are regulated by MIS; however, the researchers hope that their findings contribute towards a greater understanding of human diversity.

More information is available from the University of Otago's press release.

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Viagra helps hamsters overcome jet lag

A hamster-size dose of sildenafil, more commonly known by its marketing name Viagra, helps the rodent recover more quickly from a six-hour advance in its daily cycle, researchers report.

Originally developed for the treatment of high blood pressure and angina, Sildenafil works by interfering with an enzyme that reduces levels of a naturally-occurring compound, cyclic guanine monophosphate (cGMP). In the brain, cGMP has an important function in a signalling pathway that regulates the body’s daily clock.

Biotechnologist Patricia Agostino and colleagues at the Universidad Nacional de Quilmes in Argentina injected hamsters with sildenafil at night, before turning on bright lights six hours earlier than natural sunrise. The team then observed how the hamsters adjusted to the change, by noting how soon they began running in their exercise wheels.

Sildenafil-boosted hamsters recovered from the jet lag up to 50 percent more quickly than unassisted animals. However, the drug only worked when applied before an advance in the light/dark cycle, equivalent to an eastbound flight, rather than the reverse.

The scientists believe that frequent flyers and shift workers could benefit from moderate doses of sildenafil.

The study will be published in the U.S. journal, PNAS, this week.

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Do fruit flies have free will?

By Liz Tay
In scientific spheres, insects have a reputation similar to that of complex robots that respond predictably to their surroundings. However, a new study has claimed that fruit flies might not be as simple as previously believed, and could actually exhibit free will.

The concept of free will has been a topic of debate, even in relation to humans. Some scientists believe that the purpose of human consciousness is merely to rationalise every decision made by chemical processes in the brain a few milliseconds after the fact. Others believe that once enough is known about the human brain, it will be possible to explain and even predict a person’s behaviour.

"Given this strong claim for humans, it is surprising if prediction should be principally impossible in flies," said Björn Brembs, a biologist from the Free University Berlin and senior author of the fruit fly study. "[But] our work shows that for flies such a prediction will not be possible to the extent claimed."

Together with an international team of researchers, Brembs tethered fruit flies in completely uniform white surroundings and recorded their turning behaviour. In this setup, the flies do not receive any visual cues from the environment, and since they are fixed in space, their turning attempts have no effect.

Without any external stimuli from their surroundings, the scientists expected the flies’ behaviour to resemble random noise, similar to a radio tuned between stations. However, researchers observed the flies behaving non-randomly.

The researchers then tested a plethora of increasingly complex random computer models, all of which failed to adequately model fly behaviour, leading to the conclusion that variability in fruit fly behaviour is not due to simple random events, but is generated spontaneously and non-randomly by the brain.

Björn Brembs came up with the idea to study spontaneous behaviour almost 10 years ago in 1998, as part of his work on operant conditioning. However, as he lacked the tools required to conduct experiments, the study was put on hold until late 2004, when discussions with colleague Mark Frye sparked his interest in fruit flies.

As a biologist, Brembs is interested in the biological aspects that might enable or prevent the existence of free will. While he believes that absolute freedom is impossible, Brembs questions the extent to which humans and animals are free, and expects this to be where the species differ.

"Scientifically, the most important aspect is that we found evidence for a brain function which appears evolutionarily designed to always spontaneously vary ongoing behaviour," Brembs explained.

"There is tentative evidence that such a function may be very widespread in the animal kingdom, including humans. If this were indeed the case, we might
have discovered the first evidence for something truly fundamental," he said.

The next step will be to use genetics to localize and understand the brain circuits responsible for the spontaneous behaviour. This step could lead directly to the development of robots with the capacity for spontaneous non-random behaviour and may help combating disorders leading to compromised spontaneous behavioural variability in humans such as depression, schizophrenia or obsessive compulsive disorder.

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Happy feet hit treadmills to track climate change

By Liz Tay
They may not be able to tap dance, but king penguins in the Antarctic could in fact have a role in monitoring the effects of climate change, new research suggests.

Scientists have long studied our changing environment in terms of unusual animal behaviour, such as altering patterns of fish and bird migration. Now, a research team from the University of Birmingham is finding out if the energy requirements of king penguins could be used as an alternative bio-indicator to monitor the health of the environment.

King penguins predominantly feed on a variety of fish called myctophid fish, explained bioscientist Lewis Halsey, who led the research on Possession Island in the South Indian Ocean. As the Southern Oceans warm, these fish tend to migrate further South, and away from the Islands inhabited by king penguins, he said, which makes hunting more difficult for the penguins.

“As the king penguins have to work harder to forage for the fish, their energy expenditure in doing so will increase,” Halsey said. “[This tells] us that the myctophid fish are changing location and becoming more sparse in areas of the Southern Oceans where king penguins forage.”

King Penguin - Lewis HalseyKing penguins are good candidates as bio-indicators for several reasons, the researchers say. Firstly, while at sea foraging, they cover hundreds of kilometres and are able to dive to depths of several hundred metres, so they explore a relatively large portion of the expansive Southern Oceans. Secondly, the diets of several populations of king penguins are well known. Thirdly, while foraging for food is done at sea the penguins also come ashore to breed and moult, making them accessible to researchers.

To ascertain the penguins’ energy requirements, researchers have implanted miniature heart rate data loggers into the birds. The penguins’ heart rates are then collaborated against energy expenditure under laboratory conditions, by getting the penguins to walk on a treadmill at different speeds. This data provides a correlation between heart rate and rate of energy expenditure, so any heart rate data subsequently obtained when the king penguins go to sea to forage can be used to estimate energy expenditure.

“We have deployed these loggers on birds for several years so we can look to see if the energy expended by king penguins from year to year is changing, which may give us information on the availability of myctophid fish in the Southern Oceans each year,” Halsey said.

More data is needed from the heart rate loggers during the next few years before any long term trends can be established. If the energy expended by king penguins at sea increases over time, it is likely that myctophid fish are getting harder to come by, which could be due to the warming of the Southern Oceans, Helsey said.

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Cane toads invade new Australian terrain

By Liz Tay
As the nursery rhyme goes, there was an old lady who swallowed a fly. To catch the fly, she swallowed a spider. To catch the spider she swallowed a bird … and so on, until she died, of course.

Cane toads first reached Australian soil under similar premises. When they were introduced to the Northern Territory in 1935, they were expected to combat the cane beetle, which is a pest of sugar cane crops. While the toads did not alleviate the problem with beetles, they did quickly become accustomed to the Australian climate, and they bred fast. Farmers soon found themselves faced with larger, wartier pests than cane beetles – the cane toads themselves.

For the past 70 years, residents of Perth and Adelaide have watched cane toads spread from the Northern Territory through tropical Australia, and thought it had nothing much to do with them. But new research by an international team of scientists, including ecologist Rick Shine of the Sydney University’s School of Biological Science, claims otherwise.

March of the toads

Previous predictions about the behaviour of cane toads, which go by the scientific name Bufo marinus, indicated that the species would be limited to tropical environments like those in Central and South America, from which the toads were originally imported.

Confounding these beliefs, the toads were now found to have adapted to dry conditions and temperatures ranging from 5 to 27 degrees Celsius.

“The toads have adapted rapidly to Australian conditions, and now tolerate much higher temperatures than was the case when they first arrived on our shores in 1935,” Shine said. “As a result, toads have managed to spread much further, into climatic zones also found widely through southern Australia – so there is no reason to think they will remain only in the tropics.”

Mathematical modelling by Shine and his team shows now predicts that toads will be able to live and breed in large areas of Western Australia, South Australia and western Victoria, and in several pockets along the New South Wales coast.


Current and projected range of invasive cane toads in Australia - Rick Shane et al

The researchers estimate the toads’ range to be about 1.2 million square kilometres across the Northern Territory and Queensland. This is a dramatic increase from estimates made by the same research team a little over a year ago, in which cane toads were thought to have spread to more than a million square kilometres in tropical and sub-tropical Australia.

Additionally, the rate at which cane toads are invading is not only fast – it’s also getting faster, researchers found. Compared with a rate of only 10 kilometres a year in the 1940s, the toads are now found to be advancing at more than 50 kilometres annually. Researchers speculate that this could be a result of evolution, as toads with longer legs were found to have an evolutionary advantage over shorter-legged counterparts.

Beware warty hitch-hikers

Most of the potential range of the cane toad in southern Australia is separated from the toads’ tropical range by very large expanses of desert, which the researchers expect to be too dry for a toad to cross.

But although the toads may initially be deterred by these dry expanses, Shine said it is likely that the toads will cross such areas as hitch-hikers among rubbish or equipment in the back of a truck.

According to Shine, a nationwide invasion of cane toads is ‘inevitable’.

“[The arrival of cane toads] will probably depend upon fortuitous hitch-hiking events, rather than the toads dispersing all the way under their own steam,” he said. “The toads are superb invaders, and so far, none of the attempts to slow them down seem to have been very successful.”

Due to their toxicity and eating habits, the arrival of cane toads could spell bad news for some native fauna, pets and large predators. However, Shine expects most species to be relatively unaffected.

“Our work in the Northern Territory indicates that the toads dramatically affect only a few species,” he said, “[which are] mostly large predators like goannas, that try to eat the toads and are poisoned as a result.”

The spread of cane toads is expected to provide a good model system for understanding what invasive species will do in general, Shine said. Researchers are now expecting similar shifts in other invaders as well, as they adapt to the Australian climate.

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Genetically modified pigs could yield organs for human bodies

By Liz Tay
Recent medical advances may shine new hope on the otherwise dismal shortage of human organ donors, by allowing the organs of animals to be transplanted into human bodies instead. It may be awhile yet before the technology, known as xenotransplantation, reaches medical clinics; but when that happens, accusing someone of being pigheaded may take on a new meaning altogether.

Xenotransplantation has been studied and attempted for over a century, but few operations have been successful to date. According to Muhammad Mohiuddin, who studies xenotransplantation at the U.S. National Heart, Lung, and Blood Institute (NHLBI), the major stumbling block of existing techniques is that the immune system in the animal receiving the organ tends to reject the transplant.

"We are still learning about new immunological hurdles and have to overcome these barriers in non-human transplant models," Mohiuddin said.

To study these immunological issues, scientists have studied xenotransplantation across several animal combinations, including the insertion of hamster organs into rats, and later into mice, as well as the transplantation of organs from pigs to baboons.

In a recent paper published in the esteemed journal PLoS Medicine, Mohiuddin cites a study in which insulin-producing cells, called islets, from pigs were transplanted into monkeys with diabetes. This led to the complete reversal of diabetes for over 100 days, researchers said.

However, suppressing immunological issues in the pig-to-monkey studies involved giving the monkeys drugs called immunosuppressants in doses that would be too large to be administered in humans. To overcome the need for overly large amounts of immunosuppressants, Mohiuddin suggests organs be farmed from pigs that are genetically modified to be more compatible with humans.

"Taking out some molecules which are immunogenic to humans and putting in human molecules [in the pig] will make the pig organ more compatible to humans," he said. "This allows us to use safer immunosuppression methods, which are now routinely used in allotransplantation [organ transplantation from human to human]."

Pigs were chosen as potential donors for their organ size, which is said to be comparable to human organs, their short breeding cycle and large litter size, and our ability to genetically manipulate their immune system, Mohiuddin explained.

While there are still some hurdles between current research and the potential use of pigs in human organ donation, such as the objections of animal rights proponents and concerns to do with the transmission of viruses across species, Mohiuddin believes there is a strong case for further research into xenotransplantation.

"In [the] United States alone there are more than 90,000 patients waiting for organ transplantation and only 25,000 transplants were performed during last year," he said. "Most of these patients will die waiting for the organs."

"Xenotransplantation has the potential to save many lives," he said.

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