The new species of giant stork, named Leptoptilos robustus, stood 1.8m tall and weighed up to 16kg researchers estimate, making it taller and much heavier than living stork species.
Palaeontologist Hanneke Meijer of the Smithsonian National Museum of Natural History in Washington DC, and affiliated to the National Museum of Natural History in Leiden, the Netherlands, made the discovery with colleague Dr Rokus Due of the National Center for Archaeology in Jakarta, Indonesia.
They found fossilised fragments of four leg bones in the Liang Bua caves on the island of Flores.
The bones, thought to be belong to a single stork, are between 20,000 to 50,000 years old, having been found in sediments dating to that age.
The giant bird is the latest extreme-sized species to be discovered once living on the island, which was home to dwarf elephants, giant rats and out-sized lizards, as well as humans of small stature.
"I noticed the giant stork bones for the first time in Jakarta, as they stood out from the rest of the smaller bird bones. Finding large birds of prey is common on islands, but I wasn't expecting to find a giant marabou stork," Dr Meijer told the BBC.
Only fragments of wing bones were found, but the researchers suspect the giant stork rarely, if at all, took flight.
Instead, the size and weight of its leg bones, and the thickness of the bone walls, suggest that the now extinct stork was so heavy that it lived most of its life on the ground. It is thought to have evolved from flying storks that colonised the relatively isolated island.
Artist’s impression of the size of the giant stork next to a Homo floresiensis hobbit
"Flores has never been connected to mainland Asia and has always been isolated from surrounding islands. This isolation has played a key role in shaping the evolution of the Flores fauna," says Dr Meijer.
Many species on the islands evolved into either giants or dwarfs.
This phenomenon is known as the "island factor", and is thought to have been triggered by few mammalian predators being on the island. That led to abundant prey species becoming smaller, and other predators becoming larger. "Larger mammals, such as elephants and primates, show a distinct decrease in size, whereas the smaller mammals such as rodents, and birds, have increased in size," explains Dr Meijer.
Among the giants evolved the giant stork, and the giant rat, Papagomys armandvillei , as well as Komodo dragons, the largest surviving species of lizard. Dwarf species included the dwarfed elephant, Stegodon florensis insularis, and the human species , popularly known as the 'hobbit' H. floresiensis . Indeed, the remains of the giant stork were found in the same section of cave as the remains of H. floresiensis .
Discovered in 2004, H. floresiensis is thought to be a new human-like species standing just 1m tall, which survived until around 17,000 years ago. It is thought to be descended from a prehistoric species of human - perhaps H. erectus - which reached island South-East Asia more than a million years ago.
"The status of this human contemporary has been subject of intense debate since its discovery," says Dr Meijer. "But in my opinion, the associated fauna is crucial in understanding the evolution of H. floresiensis ."
The distinct difference in size between the 1.8 m-tall giant stork L. robustus and 1m-tall the tiny hominin H. floresiensis raises some interesting questions.
Would the hominin have eaten the giant stork? Direct evidence of H. floresiensis 's diet is hard to come by, but it is suspected of hunting animals on the island for meat. However, modern marabou storks mainly eat carrion, but they do take fish, frogs, and small mammals and birds.
So would the giant stork eaten the hominin? "Whether or not this animal may have eaten hobbits is speculative: there is no evidence for that," Dr Meijer told the BBC. "But can not be excluded either."
The giant storks towered over the hobbits. More importantly, juvenile hobbits were no bigger than giant rats that existed on the island, which themselves may have fallen prey to the giant stork, she adds.
As yet is it unclear why the giant stork, and the pygmy elephants and hobbit hominins, went extinct.
"But we have several clues," says Dr Meijer. "All the bones of the giant marabou as well as those of the pygmy elephants and the hobbits are found below a thick layer of volcanic ash," suggesting a recent volcanic eruption. "Second, the giant marabou and its contemporaries go extinct right before modern humans appear at the cave."
Around 15,000 years ago, the climate of Flores went from dry to being wetter, and a combination of any of these factors may have been enough to drive species on the islands to extinction.
Eliminating tooth decay: Breakthrough in dental plaque research
Dutch professors Bauke Dijkstra and Lubbert Dijkhuizen have deciphered the structure and functional mechanism of the glucansucrase enzyme that is responsible for dental plaque sticking to teeth.
This knowledge will stimulate the identification of substances that inhibit the enzyme. Just add that substance to toothpaste, or even sweets, and caries will be a thing of the past. The results of the research have been published this week in the journal Proceedings of the National Academy of Sciences (PNAS).
The University of Groningen researchers analysed glucansucrase from the lactic acid bacterium Lactobacillus reuteri, which is present in the human mouth and digestive tract. The bacteria use the glucansucrase enzyme to convert sugar from food into long, sticky sugar chains. They use this glue to attach themselves to tooth enamel. The main cause of tooth decay, the bacterium Streptococcus mutans, also uses this enzyme. Once attached to tooth enamel, these bacteria ferment sugars releasing acids that dissolve the calcium in teeth. This is how caries develops.
Using protein crystallography, the researchers were able to elucidate the three dimensional (3D) structure of the enzyme. The Groningen researchers are the first to succeed in crystallizing glucansucrase. The crystal structure has revealed that the folding mechanism of the protein is unique. The various domains of the enzyme are not formed from a single, linear amino acid chain but from two parts that assemble via a U-shaped structure of the chain; this is the first report on such a folding mechanism in the literature.
The unravelling of the 3D structure provided the researchers with detailed insight into the functional mechanism of the enzyme. The enzyme splits sucrose into fructose and glucose and then adds the glucose molecule to a growing sugar chain. Thus far the scientific community assumed that both processes were performed by different parts of the enzyme. However, the model created by the Groningen researchers has revealed that both activities occur in the same active site of the enzyme.
Dijkhuizen expects that specific inhibitors for the glucansucrase enzyme may help to prevent attachment of the bacteria to the tooth enamel. Information about the structure and functional mechanism of the enzyme is crucial for developing such inhibitors. Thus far, such research has not been successful, states Dijkhuizen: ‘The various inhibitors studied not only blocked the glucansucrase, but also the digestive enzyme amylase in our saliva, which is needed to degrade starch.’
The crystal structure also provides an explanation for this double inhibition. The data published by the Groningen scientists shows that glucansucrase proteins most likely evolved from amylase enzymes that degrade starch. ‘We already knew that the two enzymes were similar’, says Dijkhuizen, ‘but the crystal structure revealed that the active sites are virtually identical. Future inhibitors thus need to be directed towards very specific targets because both enzymes are evolutionary closely related.’
Dijkhuizen points out that in future glucansucrase inhibitors may be added to toothpaste and mouthwash. ‘But it may even be possible to add them to sweets’, he suggests. ‘An inhibitor might prevent that sugars released in the mouth cause damage.’ However, Dijkhuizen doesn’t expect that toothbrushes have had their day: ‘it will always be necessary to clean your teeth.’
More information: Remarkable fold of a 117 kDa glucansucrase fragment: Insights into evolution and product specificity of GH70 enzymes. Authors: Andreja Vujicić-Žagar, Tjaard Pijning, Slavko Kralj, Cesar A. López, Wieger Eeuwema, Lubbert Dijkhuizen and Bauke W. Dijkstra. PNAS, 30 November 2010. The article is published at: http://www.pnas.or … s.1007531107 Provided by University of Groningen
Scientists discover brain's inherent ability to focus learning
Medical researchers have found a missing link that explains the interaction between brain state and the neural triggers responsible for learning, potentially opening up new ways of boosting cognitive function in the face of diseases such as Alzheimer's as well as enhancing memory in healthy people.
Much is known about the neural processes that occur during learning but until now it has not been clear why it occurs during certain brain states but not others. Now researchers from the University of Bristol have been able to study, in isolation, the specific neurotransmitter which enhances learning and memory.
Acetylcholine is released in the brain during learning and is critical for the acquisition of new memories. Its role is to facilitate the activity of NMDA receptors, proteins that control the strength of connections between nerve cells in the brain.
Currently, the only effective treatment for the symptoms of cognitive impairment seen in diseases such as Alzheimer's is through the use of drugs that boost the amount of acetylcholine release and thereby enhance cognitive function.
Describing their findings in the journal Neuron, researchers from Bristol's School of Physiology and Pharmacology have shown that acetylcholine facilitates NMDA receptors by inhibiting the activity of other proteins called SK channels whose normal role is to restrict the activity of NMDA receptors.
This discovery of a role for SK channels provides new insight into the mechanisms underlying learning and memory. SK channels normally act as a barrier to NMDA receptor function, inhibiting changes in the strength of connections between nerve cells and therefore restricting the brain's ability to encode memories. Findings from this latest research show that the SK channel barrier can be removed by the release of acetylcholine in the brain in order to enhance our ability to learn and remember information.
Lead researcher Dr Jack Mellor, from the University of Bristol's Medical School, said: "These findings are not going to revolutionise the treatment of Alzheimer's disease or other forms of cognitive impairment overnight. However, national and international funding bodies have recently made research into aging and dementia a top priority so we expect many more advances in our understanding of the mechanisms underlying learning and memory in both health and disease."
The team studied the effects of drugs that target acetylcholine receptors and SK channels on the strength of connections between nerve cells in animal brain tissue. They found that changes in connection strength were facilitated by the presence of drugs that activate acetylcholine receptors or block SK channels revealing the link between the two proteins.
Dr Mellor added: "From a therapeutic point of view, this study suggests that certain drugs that act on specific acetylcholine receptors may be highly attractive as potential treatments for cognitive disorders. Currently, the only effective treatments for patients with Alzheimer's disease are drugs that boost the effectiveness of naturally released acetylcholine. We have shown that mimicking the effect of acetylcholine at specific receptors facilitates changes in the strength of connections between nerve cells. This could potentially be beneficial for patients suffering from Alzheimer's disease or schizophrenia."
The research team involved the University of Bristol's MRC Centre for Synaptic Plasticity and the Division of Neuroscience in the School of Physiology & Pharmacology, part of the Bristol Neuroscience network. This work was supported by the Wellcome Trust, MRC, BBSRC and GSK.
Paper: Facilitation of Long-Term Potentiation by Muscarinic M1 Receptors is mediated by inhibition of SK channels, by Buchanan KA, Petrovic MM, Chamberlain SEL, Marrion NV & Mellor JR in Neuron.
Study suggests cranberry juice not effective against urinary tract infections
Drinking cranberry juice has been recommended to decrease the incidence of urinary tract infections, based on observational studies and a few small clinical trials.
However, a new study published in the January 1 issue of Clinical Infectious Diseases, and now available online (http://cid.oxfordjournals.org/content/52/1/23.full), suggests otherwise.
College-aged women who tested positive for having a urinary tract infection were assigned to drink eight ounces of cranberry juice or a placebo twice a day for either six months or until a recurrence of a urinary tract infection, whichever happened first. Of the participants who suffered a second urinary tract infection, the cranberry juice drinkers had a recurrence rate of almost 20 percent, while those who drank the placebo suffered only a 14 percent recurrence.
"We assumed that we would observe a 30 percent recurrence rate among the placebo group. It is possible that the placebo juice inadvertently contained the active ingredients that reduce urinary tract infection risk, since both juices contained Vitamin C," explained study author Betsy Foxman, PhD, of the University of Michigan School of Public Health in Ann Arbor. She added, "Another possibility is that the study protocol kept participants better hydrated, leading them to urinate more frequently, therefore decreasing bacterial growth and reducing urinary tract infection symptoms."
Astronomers discover, image new planet in planetary system very similar to our own
An international team of astronomers has discovered and imaged a fourth giant planet outside our solar system, a discovery that further strengthens the remarkable resemblances between a distant planetary system and our own.
The research is published Dec. 8 in the advance online version of the journal Nature. The astronomers say the planetary system resembles a supersized version of our solar system.
"Besides having four giant planets, both systems also contain two 'debris belts' composed of small rocky or icy objects, along with lots of tiny dust particles," said Benjamin Zuckerman, a UCLA professor of physics and astronomy and co-author of the Nature paper.
Our giant planets are Jupiter, Saturn, Uranus and Neptune, and our debris belts include the asteroid belt between the orbits of Mars and Jupiter and the Kuiper Belt, beyond Neptune's orbit.
The newly discovered fourth planet (known as HR 8799e) orbits a bright star called HR 8799, which lies some 129 light years from Earth and is faintly visible to the naked eye. The mass of the HR 8799 planetary system is much greater than our own. Astronomers estimate that the combined mass of the four giant planets may be 20 times greater than the mass of all the planets in our solar system, and the debris belt counterparts also contain much more mass than our own.
The new planet joins three previously discovered planets that were the subjects of a 2008 paper in the journal Science reporting the first-ever images of a planetary family orbiting a star other than our sun. Four of the co-authors of the new Nature paper, including Zuckerman, were also co-authors on that Science paper.
"This is the fourth imaged planet in this planetary system, and only a tiny percentage of known exoplanets (planets outside our solar system) have been imaged; none has been imaged in multiple-planet systems other than those of HR 8799," Zuckerman said.
All four planets orbiting HR 8799 are similar in size, likely between five and seven times the mass of Jupiter. The newly discovered planet orbits HR 8799 more closely than the other three. If it were in orbit around our sun, astronomers say, it would lie between the orbits of Saturn and Uranus.
The astronomers used the Keck II telescope at Hawaii's W.M. Keck Observatory to obtain images of the fourth planet. Zuckerman's colleagues are from Canada's National Research Council (NRC), Lawrence Livermore National Laboratory (LLNL) in California, and Lowell Observatory in Arizona.
"We reached a milestone in the search for other worlds in 2008 with the discovery of the HR 8799 planetary system," said Christian Marois, an NRC astronomer and lead author of the Nature paper. "The images of this new inner planet are the culmination of 10 years' worth of innovation, making steady progress to optimize every aspect of observation and analysis. This allows us to detect planets located ever closer to their stars and ever further from our own solar system."
"The four massive planets pull on each other gravitationally," said co-author Quinn Konopacky, a postdoctoral researcher at LLNL. "We don't yet know if the system will last for billions of years or fall apart in a few million more. As astronomers carefully follow the HR 8799 planets during the coming decades, the question of the stability of their orbits could become much clearer."
The origin of these four giant planets remains a puzzle; neither of the two main models of planet formation can account for all four. "There's no simple model that can form all four planets at their current location," said co-author Bruce Macintosh of LLNL. "It's going to be a challenge for our theoretical colleagues."
It is entirely plausible that this planetary system contains additional planets closer to the star than these four planets, quite possibly rocky, Earth-like planets, Zuckerman said. But such interior planets are far more difficult to detect, he added.
"Images like these bring the exoplanet field, which studies planets outside our solar system, into an era of exoplanet characterization," said co-author Travis Barman, a Lowell Observatory exoplanet theorist. "Astronomers can now directly examine the atmospheric properties of four giant exoplanets that are all the same young age and that formed from the same building materials."
Detailed study of the properties of HR 8799e will be challenging due to the planet's relative faintness and its proximity to its star. To overcome those limitations, Macintosh is leading an effort to build an advanced exoplanet imager, called the Gemini Planet Imager, for the Gemini Observatory. This new instrument will physically block the starlight and allow quick detection and detailed characterization of planets similar to HR 8799e. UCLA and the NRC are also contributing to Gemini Planet Imager.
James Larkin, a UCLA professor of physics and astronomy, is building a major component of the imager, which is scheduled to arrive at the Gemini South Telescope in Chile late next year.
The research reported in Nature was funded by NASA, the U.S. Department of Energy and the National Science Foundation Center for Adaptive Optics. For more information, visit the NRC's website at www.nrc-cnrc.gc.ca.
Reproductive scientists create mice from 2 fathers
Using stem cell technology, reproductive scientists in Texas, led by Dr. Richard R. Berhringer at the M.D. Anderson Cancer Center, have produced male and female mice from two fathers.
The study was posted today (Wednesday, December 8) at the online site of the journal Biology of Reproduction.
The achievement of two-father offspring in a species of mammal could be a step toward preserving endangered species, improving livestock breeds, and advancing human assisted reproductive technology (ART). It also opens the provocative possibility of same-sex couples having their own genetic children, the researchers note.
In the work reported today, the Behringer team manipulated fibroblasts from a male (XY) mouse fetus to produce an induced pluripotent stem (iPS) cell line. About one percent of iPS cell colonies grown from this XY cell line spontaneously lost the Y chromosome, resulting in XO cells. The XO iPS cells were injected into blastocysts from donor female mice. The treated blastocysts were transplanted into surrogate mothers, which gave birth to female XO/XX chimeras having one X chromosome from the original male mouse fibroblast.
The female chimeras, carrying oocytes derived from the XO cells, were mated with normal male mice. Some of the offspring were male and female mice that had genetic contributions from two fathers.
According to the authors, "Our study exploits iPS cell technologies to combine the alleles from two males to generate male and female progeny, i.e. a new form of mammalian reproduction."
The technique described in this study could be applied to agriculturally important animal species to combine desirable genetic traits from two males without having to outcross to females with diverse traits.
"It is also possible that one male could produce both oocytes and sperm for self-fertilization to generate male and female progeny," the scientists point out. Such a technique could be valuable for preserving species when no females remain.
In the future, it may also be possible to generate human oocytes from male iPS cells in vitro. Used in conjunction with in vitro fertilization, this would eliminate the need for female XO/XX chimeras, although a surrogate mother would still be needed to carry the two-father pregnancy to term.
Using a variation of the iPS technique, the researchers say "it may also be possible to generate sperm from a female donor and produce viable male and female progeny with two mothers."
The authors also caution that the "generation of human iPS cells still requires significant refinements prior to their use for therapeutic purposes."
A once fertile landmass now submerged beneath the Persian Gulf may have been home to some of the earliest human populations outside Africa, according to an article published today in Current Anthropology.
Jeffrey Rose, an archaeologist and researcher with the University of Birmingham in the U.K., says that the area in and around this "Persian Gulf Oasis" may have been host to humans for over 100,000 years before it was swallowed up by the Indian Ocean around 8,000 years ago. Rose's hypothesis introduces a "new and substantial cast of characters" to the human history of the Near East, and suggests that humans may have established permanent settlements in the region thousands of years before current migration models suppose.
In recent years, archaeologists have turned up evidence of a wave of human settlements along the shores of the Gulf dating to about 7,500 years ago. "Where before there had been but a handful of scattered hunting camps, suddenly, over 60 new archaeological sites appear virtually overnight," Rose said. "These settlements boast well-built, permanent stone houses, long-distance trade networks, elaborately decorated pottery, domesticated animals, and even evidence for one of the oldest boats in the world."
But how could such highly developed settlements pop up so quickly, with no precursor populations to be found in the archaeological record? Rose believes that evidence of those preceding populations is missing because it's under the Gulf.
"Perhaps it is no coincidence that the founding of such remarkably well developed communities along the shoreline corresponds with the flooding of the Persian Gulf basin around 8,000 years ago," Rose said. "These new colonists may have come from the heart of the Gulf, displaced by rising water levels that plunged the once fertile landscape beneath the waters of the Indian Ocean."
Historical sea level data show that, prior to the flood, the Gulf basin would have been above water beginning about 75,000 years ago. And it would have been an ideal refuge from the harsh deserts surrounding it, with fresh water supplied by the Tigris, Euphrates, Karun, and Wadi Baton Rivers, as well as by underground springs. When conditions were at their driest in the surrounding hinterlands, the Gulf Oasis would have been at its largest in terms of exposed land area. At its peak, the exposed basin would have been about the size of Great Britain, Rose says.
Evidence is also emerging that modern humans could have been in the region even before the oasis was above water. Recently discovered archaeological sites in Yemen and Oman have yielded a stone tool style that is distinct from the East African tradition. That raises the possibility that humans were established on the southern part of the Arabian Peninsula beginning as far back as 100,000 years ago or more, Rose says. That is far earlier than the estimates generated by several recent migration models, which place the first successful migration into Arabia between 50,000 and 70,000 years ago.
The Gulf Oasis would have been available to these early migrants, and would have provided "a sanctuary throughout the Ice Ages when much of the region was rendered uninhabitable due to hyperaridity," Rose said. "The presence of human groups in the oasis fundamentally alters our understanding of human emergence and cultural evolution in the ancient Near East."
It also hints that vital pieces of the human evolutionary puzzle may be hidden in the depths of the Persian Gulf.
Jeffrey I. Rose, "New Light on Human Prehistory in the Arabo-Persian Gulf Oasis." Current Anthropology 51:6 (December 2010). http://news.discovery.com/human/haiti-cholera-epidemic-linked-un.html
Haiti Cholera Outbreak Linked To UN Camp
The cholera outbreak ravaging Haiti began at a camp for UN peacekeepers from Nepal, according to new report.
The cholera outbreak ravaging Haiti began at a camp for UN peacekeepers from Nepal, according to an expert report submitted to the French foreign ministry, a source close to the matter told AFP on Tuesday.
Respected French epidemiologist Professor Renaud Piarroux conducted a study in Haiti last month and concluded the epidemic began with an imported strain of the disease that could be traced back to the Nepalese base, the official said.
"The source of the infection came from the Nepalese camp," the source told AFP, speaking on condition on anonymity as he was not authorized to discuss a report that has not yet been made public. "The starting point has been very precisely localized," he said, pointing to the UN base at Mirebalais on the Artibonite river in central Haiti. “There is no other possible explanation given that there was no cholera in the country, and taking into account the intensity and the speed of the spread and the concentration of bacteria in the Artibonite delta," he said. "The most logical explanation is the massive introduction of fecal matter into the Artibonite river on a single occasion," the source added.
The United Nations, which has faced violent protests in Haiti over its alleged role in an outbreak that has already killed 2,000 people and made 90,000 sick, insists there is no evidence that its troops were to blame.
Foreign ministry spokesman Bernard Valero did not reveal the conclusion of the report, but confirmed the foreign ministry had received a copy and said it had been passed on to the United Nations for investigation.
"From the outbreak of the epidemic, France sent to Haiti at the request of the Haitian health ministry one of its best cholera specialists, Professor Piarroux, a head of department in Marseille's public hospitals," he said.
Cholera has added to the woes of the impoverished Caribbean nation, which was devastated by a massive earthquake in January that killed a quarter of a million people and left 1.3 million living in ramshackle refugee camps. Piarroux discussed his report in an interview with AFP last month. He did not directly blame the Nepalese, but said the cholera was from abroad.
"It started in the center of the country, not by the sea, nor in the refugee camps. The epidemic can't be of local origin. That's to say, it was imported," he said, shortly after his return from Haiti.
Haitian officials say the first cases of cholera, a waterborne illness, broke out on the banks of the Artibonite river, downstream of the UN base.
Last month, Edmond Mulet, head of the United Nations mission in Haiti, said no UN soldier, police officer nor civilian official had tested positive for cholera, and he defended the Nepalese, who have been the target of protests. All samples taken from the latrines, kitchens and water supply at the suspect Nepalese camp have proved negative, Mulet said. "There is no scientific evidence that the camp at Mirebalais is the source of this epidemic," he said, complaining of "a lot of disinformation, a lot of rumors around this situation."
But Piarroux - who works at the University of the Mediterranean in Marseille - told AFP that the outbreak was not linked to the earthquake devastation, and could not have come from a Haitian environmental source.
"The epidemic exploded in an extremely violent way on Oct. 19, with several thousand cases and several hundreds deaths after many people drank the water of the Artibonite delta," he said.
The professor said the world had not seen cholera spread so quickly since an outbreak in Goma, in eastern Congo, in 1994. "We've had more than 70,000 cases, and we could easily see them hit 200,000," he warned.
Cholera is caused by bacteria spread in contaminated water or food, often through faeces. If untreated, it can kill within a day through dehydration, with the old and the young the most vulnerable.
Mammals' body temperatures may represent balance between warding off fungi and limiting food needs
By Tina Hesman Saey
Fungi may be to thank for mammals’ warm blood, a new theory suggests. But exactly how hot-blooded an animal is may depend on balancing fungal protection with food consumption.
The optimum body temperature for organisms to ward off fungal infections without burning too much energy is 36.7˚ Celsius - close to the core body temperatures of mammals, including humans, researchers at Albert Einstein College of Medicine in New York City reported online November 9 in mBio. The finding is the latest piece of evidence for a theory that fungi may have been a driving force in the evolution of mammalian body temperatures. The new mathematical analysis also helps explain why mammals aren’t even hotter.
“Mammals don’t make any sense,” says Arturo Casadevall, a microbiologist at Einstein who devised the theory. “We have to eat all the time. Our reproduction rate is low.” In fact, until catastrophic events caused the extinction of the dinosaurs, “mammals were an experiment that wasn’t going anywhere,” he says.
Casadevall wondered why reptiles didn’t retake control of the Earth once environmental conditions had stabilized again.
A couple of pieces of evidence led him to develop the new theory. First, a massive fungal bloom swept the Earth about the time of the dinosaur extinction. “The world became a huge a compost pile,” he says.
Second, fungi plague plants, insects and other cold-blooded creatures far more often than they do mammals or birds. Putting two and two together, he formulated a theory that the warm body temperatures of mammals and birds might have protected them from fungal pathogens, while diseases caused by fungi might have been a factor keeping the reptiles from rising again.
Mammals have a range of body temperatures, but most hover around 37° Celsius. Such warm bodies help protect against fungal infections, but being hotter means eating a lot more. A new study finds that 36.7°C is the optimal body temperature for striking a balance between the two. SOURCE: C. Ladd Prosser, ed. Environmental and Metabolic Animal Physiology, 4th ed. Wiley-Liss, 1991
“We are cautiously suggesting that fungi may have been responsible for the success of the mammals,” he says.
To test the theory, Casadevall and Vincent Robert of the CBS Fungal Biodiversity Center in Utrecht, the Netherlands, measured the thermal tolerance of 4,802 types of fungi. For every degree Celsius the researchers raised the temperature above 30˚ C, 6 percent fewer fungal species could grow, the team reported last year in the Journal of Infectious Diseases.
Most mammals have body temperatures of about 37˚ C (98.6˚ Fahrenheit). But if higher temperatures ward off more fungi, why don’t mammals run even hotter?
In the new paper, Casadevall and coauthor Aviv Bergman, an evolutionary systems biologist also at Einstein, attempted to answer the question with a mathematical model. Mammalian body temperature is a trade-off between fighting fungi and burning too much fuel, they found. “If you were to go higher, you’d have more protection, but then you’d have to eat a lot more,” Casadevall says.
Researchers calculated an organism's fitness as a function of body temperature, revealing 36.7°C as the ideal body temperature. Fitness - designated W(T) above - represents the balance between the benefit of fighting of fungal pathogens and the energy costs ofmaintaining a higher body temperature.A. Bergman & A. Casadevall/mBio 2010
Their model doesn’t address all the biological questions related to mammalian body temperature, says Bergman, but it does suggest that threats from fungi could impose constraints on some aspects of mammalian evolution.
“I think it’s a really cool idea,” says Leah Cowen, a medical mycologist at the University of Toronto. What’s striking about the new study is that the model is simple, “but the vision is large,” potentially answering a huge question in evolutionary biology. “This is a big picture question addressed by a simple mathematical model.”
The real mark of a good model is whether it can make predictions, says Joseph Heitman, a microbiologist and geneticist at Duke University. This model is “really creative and a bit out there,” he says, but “one of the beauties of it is that it is fairly straightforward.”
One might predict from this model that raising an animal’s temperature would lead to greater resistance to fungi. Lowering body temperature would then be expected to make animals more vulnerable to fungal infections.
Frogs and other amphibians in decline around the world - in part because of infections with a chytrid fungus - may provide some evidence that the theory is correct. Warming up infected frogs can help clear them of the fungus, Heitman says.
Reducing a mammal’s temperature in the laboratory to find out whether lower body temperatures lead to fungal disease is difficult because messing with body temperature can affect many other biological processes. But hibernating bats may provide a clue that Casadevall is onto something, says David Blehert, a microbiologist with the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis.
Blehert studies white-nose syndrome, a fungal disease that is killing bats in large numbers in the eastern United States. A fungus called Geomyces destructans infects bats while they are hibernating - a time when body temperatures drop from 40˚ C to about 7˚. “They’re not warm-blooded when they get infected,” Blehert says. When bats are up and around and at their normal body temperature, they seem impervious to the infection, he says.
In a report published November 11 in BMC Biology, Blehert and others described how the fungus, which erodes and replaces the bat’s skin, damages wings and leads to death. Casadevall’s idea has “become important in our thinking about this disease,” Blehert says.
The idea of a link between fungal disease and body temperature is not controversial among scientists, Blehert says. “It’s very logical.”