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速度：
速度1：
Spawning coral monitored for effects of climate change
The divers’ lights pierce the nighttime darkness 18 metres below the rolling waves of the Gulf of Mexico. As the beams pan across a coral reef, they illuminate whitish spheres nestled in the pale yellow ridges of female coral mounds. Triggered by some unknown signal, these eggs start to rise, a few at a time, like little helium balloons. Male corals nearby begin to release sperm, which resembles drifting smoke, or milk stirred into black coffee. Dispersed by currents, the gametes gradually ascend towards a reproductive rendezvous at the surface.
"It’s a marvellous sight of nature that most people will never see," says Larry McKinney, director of the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas. McKinney was part of a team of scientists who spent four nights last week scuba-diving and observing the annual coral spawning at the Flower Garden Banks National Marine Sanctuary, located in the Gulf about 175 kilometres southeast of Galveston, Texas.
For McKinney, the event is not only a natural wonder, but also a key indicator of reef health. “Spawning events are sort of the canary in the coal mine for reefs,” he says. Enviornmental stressors that can affect spawning include overfishing and coastal development and — to a degree that has become an increasing concern in the Gulf — water temperature.
Sexual reproduction through spawning is also crucial to reef health in a more long term sense, says Peter Vize, a biologist at the University of Calgary in Canada, because it mixes up genes to produce combinations that may help corals to adapt to climate change. Vize has studied spawning at the sanctuary, but was not present for this year's event. "If pollution or other elements, including higher than normal water temperatures, stopped corals from spawning, no new genetic diversity would be generated," he says.
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速度2：
In hot water
The 21 species of reef-building coral living in the sanctuary, which make up the most northerly reefs in North America, are adapted to live in sea water at temperatures of 20–30 °C. But in recent years, the waters of the Gulf have been experiencing above-average temperatures with increasing frequency.
If the waters get above 30 °C for much of the season, corals may 'bleach', expelling the symbiotic algae that give them their colour. Bleached corals can recover if conditions return to normal fairly quickly, but otherwise they die.
On 2 August, just before this year's spawn, the US National Oceanic and Atmospheric Administration reported higher than normal water temperatures in the Gulf and issued a coral-bleaching warning for the sanctuary. Sure enough, during last week’s dives, surface temperatures ranged from 30.2 °C to 30.5 °C.
Apart from the bleaching, no one is quite sure how warming in the Gulf will affect the spawning. Water temperature is known to be among the environmental signals that influence the exact timing of the event, but researchers have yet to tease out how various triggers — which also include the phase of the Moon and diurnal cycles — operate and interrelate. "It’s possible higher water temperatures could shift or disrupt the spawn," says McKinney.
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速度3：
Moonlight magic
Predicting the time of spawning was tricky this year, says Emma Hickerson, research coordinator at the Flower Garden Banks sanctuary. Spawning occurs between seven and ten days after the first full Moon in August, but this year the full Moon fell between 1 and 2 August, so Hickerson had to make a judgement call on which day to start the count.
"In general, it was a decent spawning event, although a bit confused," said Hickerson afterwards. "The star and brain corals typically spawn on the same night, but the star corals went off on the eighth [night] and the brain corals primarily on the ninth."
Observers commented that the spawning was not as prolific as it has been in previous years. On some occasions, the sheer volume of gametes has reduced visibility in these normally clear waters to less than a metre. However, the differences this year could be within the boundaries of natural variation. And because divers can remain underwater for only an hour or so at a time, the team might have missed the period of greatest activity.
Sanctuary scientists have been monitoring the spawning since 1991. They haven't observed any significant changes over the years, but measurements have so far been qualitative rather than quantitative. However, that is set to change: Hickerson and other researchers are working with the US Naval Research Laboratory to develop the capacity to take quantitative measurements of the amount of material released. They hope to have a system in place by next year. Eventually the data will help to illuminate the impact of factors such as temperature changes on coral reporduction.
“I think the jury is still out in regards to coral spawning in warming seas,” says Hickerson after the dive. With rising temperatures likely to become the new normal, much could rest on the eventual verdict.
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速度4:
First evidence for photosynthesis in insects
The biology of aphids is bizarre: they can be born pregnant and males sometimes lack mouths, causing them to die not long after mating. In an addition to their list of anomalies, work published this week indicates that they may also capture sunlight and use the energy for metabolic purposes.
Aphids are unique among animals in their ability to synthesize pigments called carotenoids. Many creatures rely on these pigments for a variety of functions, such as maintaining a healthy immune system and making certain vitamins, but all other animals must obtain them through their diet. Entomologist Alain Robichon at the SophiaAgrobiotech Institute in Sophia Antipolis, France,and his colleagues suggest that, in aphids, these pigments can absorb energy from the Sun and transfer it to the cellular machinery involved in energy production1.
Although unprecedented in animals, this capability is common in other kingdoms. Plants and algae, as well as certain fungi and bacteria, also synthesize carotenoids, and in all of these organisms the pigments form part of the photosynthetic machinery.
Taking their cue from the 2010 finding2 that the high levels of carotenoids found in aphids are homegrown, Robichon and his team set out to investigate why the insects make such metabolically expensive chemicals.
Carotenoids are responsible for aphid pigmentation, and an aphid's colour determines the kind of predators that can see it. The body colour of Robichon's lab aphids is affected by environmental conditions, with the cold favouring green aphids, optimal conditions resulting in orange ones and white ones appearing when the population is large and faced with limited resources.
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速度5：
When the researchers measured the aphids’ levels of ATP — the ‘currency’ of energy transfer in all living things — the results were striking. Green aphids, which contain high levels of carotenoids, make significantly more ATP than do white ones, which are almost devoid of these pigments. Moreover, ATP production rose when the orange insects — which contain an intermediate amount of carotenoids — were placed in the light, and fell when they were moved into the dark.
The researchers went on to crush the orange aphids and purify their carotenoids, demonstrating that it was these extracts that could absorb light and pass this energy on.
One of the authors, Maria Capovilla, another entomologist at the Sophia Institute, insists that much more work is needed before scientists can be sure that aphids truly photosynthesize, but the findings certainly throw up that possibility.
The way that carotene molecules are arranged in the animals adds weight to that hypothesis. The pigments form a layer between 0–40 micrometres deep under the insect's cuticle, putting them in the perfect position to capture the Sun's light.
Nancy Moran, an insect geneticist at Yale University in West Haven, Connecticut, who was responsible for the original discovery that aphids have the genes for carotenoid production, points out that there are many unanswered questions. “Energy production seems to be the least of an aphid's problems — their diet is loaded with excessive sugar, most of which they cannot use,” she says.
And that begs the question of why aphids would need to photosynthesize. But Capovilla speculates that a battery-like back-up might help them in times of environmental stress, such as when they are migrating to a new host plant.
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越障：
Me, myself, us
WHAT’S a man? Or, indeed, a woman? Biologically, the answer might seem obvious. A human being is an individual who has grown from a fertilised egg which contained genes from both father and mother. A growing band of biologists, however, think this definition incomplete. They see people not just as individuals, but also as ecosystems. In their view, the descendant of the fertilised egg is merely one component of the system. The others are trillions of bacteria, each equally an individual, which are found in a person’s gut, his mouth, his scalp, his skin and all of the crevices and orifices that subtend from his body’s surface.
A healthy adult human harbours some 100 trillion bacteria in his gut alone. That is ten times as many bacterial cells as he has cells descended from the sperm and egg of his parents. These bugs, moreover, are diverse. Egg and sperm provide about 23,000 different genes. The microbiome, as the body’s commensal bacteria are collectively known, is reckoned to have around 3m. Admittedly, many of those millions are variations on common themes, but equally many are not, and even the number of those that are adds something to the body’s genetic mix.
And it really is a system, for evolution has aligned the interests of host and bugs. In exchange for raw materials and shelter the microbes that live in and on people feed and protect their hosts, and are thus integral to that host’s well-being. Neither wishes the other harm. In bad times, though, this alignment of interest can break down. Then, the microbiome may misbehave in ways which cause disease.
That bacteria can cause disease is no revelation. But the diseases in question are. Often, they are not acute infections of the sort 20th-century medicine has been so good at dealing with (and which have coloured doctors’ views of bacteria in ways that have made medical science slow to appreciate the richness and relevance of people’s microbial ecosystems). They are, rather, the chronic illnesses that are now, at least in the rich world, the main focus of medical attention. For, from obesity and diabetes, via heart disease, asthma and multiple sclerosis, to neurological conditions such as autism, the microbiome seems to play a crucial role.
A bug’s life
One way to think of the microbiome is as an additional human organ, albeit a rather peculiar one. It weighs as much as many organs (about a kilogram, or a bit more than two pounds). And although it is not a distinct structure in the way that a heart or a liver is distinct, an organ does not have to have form and shape to be real. The immune system, for example, consists of cells scattered all around the body but it has the salient feature of an organ, namely that it is an organised system of cells.
The microbiome, too, is organised. Biology recognises about 100 large groups of bacteria, known as phyla, that each have a different repertoire of biochemical capabilities. Human microbiomes are dominated by just four of these phyla: the Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. Clearly, living inside a human being is a specialised existence that is appropriate only to certain types of bug.
Specialised; but not monotonous. Just as ecosystems such as forests, grasslands and coral reefs differ from place to place, so it is with microbiomes. Those of children in Malawi and rural Venezuela, for instance, contain more riboflavin-producing bugs than do those of North Americans. They are also better at extracting nutrition from mother’s milk because they turn out lots of an enzyme known as glycoside hydrolase. This converts carbohydrates called glycans, of which milk has many, into usable sugars.
That detail is significant. Glycans are indigestible by any enzyme encoded in the 23,000 human genes. Only bacterial enzymes can do the job. Yet natural selection has stuffed milk full of them—a nice example of co-evolution at work.
This early nutritional role, moreover, is magnified throughout life. Like the glycans in milk, a lot of carbohydrates would be indigestible if all the digestive system had to work with were the enzymes that it makes for itself. The far larger genome of the microbiome has correspondingly greater capabilities, and complex carbohydrates are no match for it. They are relentlessly chewed up and their remains spat out as small fatty-acid molecules, particularly formic acid, acetic acid and butyric acid, that can pass through the gut wall into the bloodstream—whence they are fed into biochemical pathways that either liberate energy from them (10-15% of the energy used by an average adult is generated this way) or lay them down as fat.
The fat of the land
This role in nutrition points to one way in which an off-kilter microbiome can affect its host: what feeds a body can also overfeed or underfeed it. One of the first analyses of such an effect was Jeffrey Gordon’s work on bacteria and obesity. In 2006 Dr Gordon, who works at the Washington University School of Medicine, in St Louis, Missouri, published a study that looked at the mixture of bacteria in the guts of fat and thin Americans. Fat people, he discovered, had more Firmicutes and fewer Bacteroidetes than thin ones. And if dieting made a fat person thin, his bacterial flora changed to match.
Experiments on mice suggest this is not just a question of the bacteria responding to altered circumstances. They actually assist the process of slimming by suppressing production of a hormone that facilitates the storage of fat, and of an enzyme that stops fat being burned. This may help explain an otherwise weird observation from agriculture, which is that adding antibiotics to cattle feed helps fatten beasts up—though cattle treated in this way put on muscle mass as well as fat.
Having shown that gut bacteria are involved in obesity, Dr Gordon wondered if the converse was true. In a study he conducted in Malawi, he revealed at a meeting last year, he found that it is. Having the wrong sort of bacteria can cause malnutrition, too.
To show this, he and his team looked at 317 pairs of twins (some fraternal, some identical). In 43% of these pairs, both members were well nourished. In 7% both were malnourished. Crucially, though, in 50% of them one twin was well nourished and one malnourished.
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发表于 2012-8-20 12:17:25
排版很棒~~~ 我就中意12号字
