【Native Speaker每日训练计划—94系列】【94-19】科技

seal627

内容: Ada Yin 编辑: Cecile Zhang

Wechat ID: NativeStudy  /Weibo: http://weibo.com/u/3476904471

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Part I: Speaker

Australian Bird Dips ItsDinner

Jason G. Goldman 丨 September 29, 2017

[Rephrase 1, 02’38]

Source: Scientific American

https://www.scientificamerican.com/podcast/episode/australian-bird-dips-its-dinner/

Part II: Speed

Giant Tree-Dwelling, Coconut-Eating Rat Species Discovered

Jason G. Goldman 丨 September 27, 2017

[Time 2]

On his first trip to the Solomon Islands in 2010 Tyrone Lavery heard rumors about a strange rodent on Vangunu Island. The giant rat, according to locals, lived in the rainforest canopy and could crack open coconuts with its teeth.

Vangunu is situated some 1,000 miles northwest of Australia, at the western end of the 900-plus-island archipelago. The “vika,” as the creature is known, was apparently once familiar enough that it featured in Vangunu children’s songs and nursery rhymes. Scientists had been hearing about the rats from locals since at least the early 1990s, but none of these researchers had ever seen one.

To determine whether the rodent was a new species, all Lavery, a mammalogist at Chicago’s Field Museum, had to do was find one. That proved more difficult than it sounds. “We put out camera traps, placed [mammal] traps in trees, searched hollow trees [and] spotlighted,” he says, referring to a wildlife surveying method that involves using a flashlight to detect light reflecting from animals’ eyes at night. Beyond a single piece of rodent poop, “we hadn't been able to find any sign of it,” he says. “Until now."

Hikuna Judge, a wildlife ranger from the Zaira Conservation Area, happened to be in the right place at the right time when he spotted and captured a large rodent scampering away from a felled tree. Local elders confirmed this creature was indeed the mysterious vika, and after comparing the specimen to other known rats, Lavery verified the species had never been documented scientifically. Lavery and Judge announced their discovery and described the new species Wednesday, in the Journal of Mammalogy. They called it Uromys vika, in honor of its local name.

[282 words]

[Time 3]

The odd creature is the first new Solomon Islands rodent to be described in more than 80 years. David Boseto, a Solomons-based ecologist who was not involved in the study, says this feat would likely have been impossible if not for Lavery's work to engage indigenous communities with the research, underlining the importance of incorporating local knowledge into the process of scientific discovery.

Unlike the 200-gram (seven-ounce) common street rat, this critter weighs nearly a kilogram (2.2 pounds), and measures 46 centimeters (18 inches) from nose to tail. It excavates holes in coconuts with its teeth to reach the meat and juice inside. The Vangunu giant rat—the creature's common name—is presumed to live in the tree canopy where it feasts on fruits and nuts, as revealed by analysis of specimen and scat samples. It occupies the ecological role filled by similar-size mammals in other rainforests, such as opossums or small monkeys. Its only natural predators are raptors like the Solomon sea eagle. The rats must also contend with the threat of feral cats, which have the dubious distinction of being the animals that appeared most frequently on Lavery's camera traps.

But humans pose the biggest threat. “Like most islands in the Solomons, over 90 percent of the land is still owned by indigenous people,” Lavery says of Vangunu. The people there live a subsistence lifestyle, growing vegetables in their gardens, fishing from the reefs and hunting in the rainforests. But foreign timber companies have begun enticing local communities with nearly irresistible financial offers in exchange for logging rights. As a result, the tree-dwelling Vangunu giant rat appears completely absent from areas of the island that have been subject to intensive logging.

[283 words]

[Time 4]

There is good news for the massive rodents, however. The Zaira Conservation Area encompasses three zones within the rainforest. Hunting is only allowed in one zone at a time, giving biodiversity in the hunter-free areas several years to recover before exploitation begins once again. (The rats are not hunted themselves but by rotating the hunting blocks the community ensures that all the rainforest's inhabitants have a chance to recover from the direct and indirect impacts of human activities.) The Zaira community has so far resisted encroachment by logging companies. Therefore, this conservation area is one of the few places on the island where the rat continues to survive. The researchers argue the species should be designated as “critically endangered,” in part because its already small habitat continues to disappear.

If not for Lavery's persistence and Judge’s serendipitous sighting, the vika might have vanished before it had ever been described scientifically. Now Lavery has shifted his species quest to the nearby island of Malaita, where locals tell him of a type of bat they call the monkey-faced bat. “It’s possible it might have already become extinct,” he says. But he's looking for it anyway.

[193 words]

Source: Science News

https://www.scientificamerican.com/article/giant-tree-dwelling-coconut-eating-rat-species-discovered/

Toad tadpoles turn homegrown poisons on each other

Christie Wilcox | 29 September 2017

[Time 5]

Many tadpoles ward off predators with potent poisons — but those toxins also seem to help win battles with their own kind, a new study finds.

Tadpoles of common toads (Bufo bufo) are more poisonous when raised in crowded conditions, which may give them a competitive edge, according to the work published on 23 September in Functional Ecology1.

Many noxious plant species are known to modulate their defences to fend off different threats2, but it is less clear whether animals possess similar toxin-tuning abilities. Although predation pressure is known to induce tadpole chemical defences3, the new findings are the first unequivocal evidence of toxin synthesis spurred by competition in vertebrate animals.

Being poisonous can make a species essentially inedible to predators, but making potent toxins comes at a metabolic cost — so it’s best to make that investment count. “It would be very profitable for such animals to kill two birds with one stone by using their anti-predatory toxins as chemical weapons against their competitors, too,” says the study’s lead author, Veronika Bókony, an ecologist with the Hungarian Academy of Sciences in Budapest.

Common toads are equipped with bufadienolides, potent toxins that cause harm by accelerating and disrupting the heart’s rhythms4. Field studies have found that common toad toxicity varies geographically, with the intensity of competition being the most reliable predictor5. But it has been unclear whether such patterns occur because populations are genetically isolated from one another in different ponds, or whether they reflect defences induced by environmental factors.

Bókony and her colleagues took this question to the laboratory, rearing toads in artificial ponds with varying numbers of individuals — a proxy for the strength of competition. The species composition of the ponds also varied; some contained common toads, others contained agile frogs (Rana dalmatina) and some contained a mix. Agile frogs hatch earlier and grow to larger sizes than common toads, so they were considered to represent tougher competition. Because the frogs are non-toxic, the researchers wanted to see whether the toads’ toxins are especially aimed at these intense rivals (a phenomenon called allelopathy).

[343 words]

[Time 6]

Toxic relationships

The more competitors the toads were raised with — of either species — the smaller and more toxic they were, echoing the field results. But surprisingly, toad tadpoles defended themselves against their own kind more fiercely, by producing more toxins than they did against the frogs. Meanwhile, the frogs didn’t seem to be bothered by their toxic tankmates.

The study is “very well designed”, says Thomas Hossie, an ecologist at Trent University in Peterborough, Canada. The plasticity of other tadpole traits, including morphology and behaviour, is well documented, he notes, but most studies examine the response to predation risk. “This paper is another great example of how amazingly plastic larval amphibian traits really are.”

Gary Bucciarelli, an ecologist at the University of California, Los Angeles, also praises the work: “I think the researchers present a very compelling study that questions the evolution and ecological role of amphibian chemical defences.” His own research has shown that newts become more toxic in response to stressful conditions6. Such findings “really begin to scrutinize the idea that predation alone drives variation in animal chemical defences”, he adds.

Toxicity that varies by the density of an organism’s population has also been observed in insects7, notes Hossie: “This experiment indicates that it may be more widespread than we anticipated.”

Bókony and her colleagues aren’t done with the toads yet, as the unexpected lack of harm to the competitor frogs “begs the question what exactly [the toads] are defending themselves from”. Cannibalism is certainly a possibility, as tadpoles of many species are known to turn on their own when times are tough.

But Bókony wonders whether the toxins might serve a different function altogether. She hypothesizes they may “provide a sort of immune defence against contagious diseases they could catch from [fellow tadpoles], especially when crowded”. She and her colleagues hope to explore this possibility next.

[309 words]

Source: Nature

https://www.nature.com/news/toad-tadpoles-turn-homegrown-poisons-on-each-other-1.22734

Part III: Obstacle

Why poison frogs don't poison themselves

University of Texas at Austin | September 21, 2017

[Paraphrase 7]

Don't let their appearance fool you: Thimble-sized, dappled in cheerful colors and squishy, poison frogs in fact harbor some of the most potent neurotoxins we know. With a new paper published in the journal Science, scientists are a step closer to resolving a related head-scratcher -- how do these frogs keep from poisoning themselves? And the answer has potential consequences for the fight against pain and addiction.

The new research, led by scientists at The University of Texas at Austin, answers this question for a subgroup of poison frogs that use the toxin epibatidine. To keep predators from eating them, the frogs use the toxin, which binds to receptors in an animal's nervous system and can cause hypertension, seizures, and even death. The researchers discovered that a small genetic mutation in the frogs -- a change in just three of the 2,500 amino acids that make up the receptor -- prevents the toxin from acting on the frogs' own receptors, making them resistant to its lethal effects. Not only that, but precisely the same change appeared independently three times in the evolution of these frogs.

"Being toxic can be good for your survival -- it gives you an edge over predators," said Rebecca Tarvin, a postdoctoral researcher at UT Austin and a co-first author on the paper. "So why aren't more animals toxic? Our work is showing that a big constraint is whether organisms can evolve resistance to their own toxins. We found evolution has hit upon this same exact change in three different groups of frogs, and that, to me, is quite beautiful."

There are hundreds of species of poisonous frogs, each of which uses dozens of different neurotoxins. Tarvin is part of a team of researchers, including professors David Cannatella and Harold Zakon in the Department of Integrative Biology, who have been studying how these frogs evolved toxic resistance.

For decades, medical researchers have known that this toxin, epibatidine, also can act as a powerful nonaddictive painkiller. They've developed hundreds of compounds from the frogs' toxin, including one that advanced in the drug-development process to human trials before being ruled out due to other side effects.

The new research -- showing how certain poison frogs evolved to block the toxin while retaining use of receptors the brain needs -- gives scientists information about epibatidine that could eventually prove helpful in designing drugs such as new pain relievers or drugs to fight nicotine addiction.

"Every bit of information we can gather on how these receptors are interacting with the drugs gets us a step closer to designing better drugs," said Cecilia Borghese, another co-first author of the paper and a research associate in the university's Waggoner Center for Alcohol and Addiction Research.

Changing the Lock

A receptor is a type of protein on the outside of cells that transmits signals between the outside and the inside. Receptors are like locks that stay shut until they encounter the correct key. When a molecule with just the right shape comes along, the receptor gets activated and sends a signal.

The receptor that Tarvin and her colleagues studied sends signals in processes like learning and memory, but usually only when a compound that is the healthy "key" comes into contact with it. Unfortunately for the frogs' predators, toxic epibatidine also works, like a powerful skeleton key, on the receptor, hijacking cells and triggering a dangerous burst of activity.

The researchers found that poison frogs that use epibatidine have developed a small genetic mutation that prevents the toxin from binding to their receptors. In a sense, they've blocked the skeleton key. They also have managed, through evolution, to retain a way for the real key to continue to work, thanks to a second genetic mutation. In the frogs, the lock became more selective.

Fighting Disease

The way that the lock changed suggests possible new ways to develop drugs to fight human disease.

The researchers found that the changes that give the frogs resistance to the toxin without changing healthy functioning occur in parts of the receptor that are close to, but don't even touch epibatidine. Borghese and Wiebke Sachs, a visiting student, studied the function of human and frog receptors in the lab of Adron Harris, another author on the paper and associate director of the Waggoner Center.

"The most exciting thing is how these amino acids that are not even in direct contact with the drug can modify the function of the receptor in such a precise way," Borghese said. The healthy compound, she continued, "keeps working as usual, no problem at all, and now the receptor is resistant to epibatidine. That for me was fascinating."

Understanding how those very small changes affect the behavior of the receptor might be exploited by scientists trying to design drugs that act on it. Because the same receptor in humans is also involved in pain and nicotine addiction, this study might suggest ways to develop new medications to block pain or help smokers break the habit.

Retracing Evolution

Working with partners in Ecuador, the researchers collected tissue samples from 28 species of frogs -- including those that use epibatidine, those that use other toxins and those that are not toxic. Tarvin and hear colleagues Juan C. Santos from St. John's University and Lauren O'Connell from Stanford University sequenced the gene that encodes the particular receptor in each species. She then compared subtle differences to build an evolutionary tree representing how the gene evolved.

This represents the second time that Cannatella, Zakon, Tarvin and Santos have played a role in discovering mechanisms that prevent frogs from poisoning themselves. In January 2016, the team identified a set of genetic mutations that they suggested might protect another subgroup of poison frogs from a different neurotoxin, batrachotoxin. Research published this month was built on their finding and conducted by researchers from the State University of New York at Albany, confirming that one of UT Austin's proposed mutations protects that set of poison frogs from the toxin.

The paper's other co-author is Ying Lu of UT Austin.

Funding for this project was provided by the National Geographic Society, the National Science Foundation, the UT Waggoner Center for Alcohol and Addiction Research, the National Institutes of Health and seven academic societies.

[1040 words]

Source: Science Daily

https://www.sciencedaily.com/releases/2017/09/170921141238.htm

butterfly_memo

T2 1:18.70
T3 1:33.46
T4 1:66.36
T5 1:29.34
T6 1:58.14

白鹤君

Speed

T2: 1:28
T3: 1:47
T4: 1:04
T5: 2:05
T6: 1:54

萨拉邦德

1004
94-19
T2[282 words] 1’49
在远离澳大利亚的一个岛屿上新发现一种巨大型老鼠，这种老鼠生活在树上，并能咬开椰子壳。
rodent
canopy
coconuts
hollow
T3[283 words] 1’51
没有当地的帮助就不会有这样的发现
indigenous
feasts
contend with
dubious
irresistible
T4[193 words] 1’11
限制采伐保护物种。
serendipitous
quest
T5[343 words] 2‘16
研究蝌蚪是否会毒同类
noxious
modulate
T6[309 words] 1‘56
竞争越大，毒素越强，而且对自己种族毒性越强。
echoing
plasticity
contagious

dsy0506

T2:01:31
T3:01:52
T4:01:11
serendipitous 偶然发现的 encroachment 侵犯，入侵
T5:02:28
modulate 调节，调制 cannibalism 嗜食同类的行为
T6:01:52
OB:05:45

小绵羊的春天

【1 02:00】
L发现了一种罕见的rat
【2 02:21】
没有L的功绩就不能发现这种rat，介绍了这种rat的体态，饮食，天敌。而现在有商业用途
【3 01:13】
好在捕猎一次只能在一个区域进行，给物种恢复数量提供时间。而目前发现这些rat正在转移住所，也许已经灭绝。
【4 02:44】
某种蟾蜍能产生很强的毒液，但由于这种能力是在面临敌人靠新陈代谢的，最好每次释放毒液能达到目的。科学家做了一个实验
【5 02:35】
实验发现，敌人越多的蟾蜍，毒液越少；反而当和同类在一起时，毒液增加。科学家觉得分泌毒液也许还有别的目的：为了不从同类中获得疾病

johnnya

1:39
1:14
0:51
1:23
1:30

riddles

October4 94-19科技
Time2:02:15
Time3:02:33
Time4:02:56
Time5:02:34
Time5:02:12

dengma

T2:2:23.73
T3:2:03.23
T4:1:37.63
T5:2:44.24
T6:1:41.68

合水鸡小姐

T2:01:54.83
T3:02:14.91
T4:01:17.66
T5:02:26.41
T6:01:40.58