快猫短视频

On a windswept moor in England, a large black creature crouches alert and
tense, before continuing its midnight prowl. Silhouetted against the night sky,
it reaches the crest of a hill, and passes behind a tree. There it pauses,
scuffles around, strains briefly, and leaves. Is this the Beast of Bodmin
Moor?

For decades, walkers have claimed to see a large cat-like creature, perhaps a
leopard, perhaps a puma, perhaps something even stranger, prowling over Bodmin
Moor in Cornwall. Local farmers have reported suspicious deaths among their
sheep and cattle. Although Britain鈥檚 Ministry of Agriculture has dismissed the
whole thing as rubbish after reviewing videotapes and footprint casts, and
although London鈥檚 Natural History Museum claims that the large-fanged cat skull
found on the moor is not native to England (it contained the egg case of a
tropical cockroach), the locals think they know better.

Luckily, this time, during its brief pause behind the tree, the creature has
left a new kind of evidence. At first glance it may seem less compelling than
eyewitness accounts, but it holds a treasure trove of incontrovertible
scientific evidence. It鈥檚 a pile of dung鈥攈umble faeces鈥攖hat is
chock-full of DNA from cells sloughed off the creature鈥檚 digestive tract. It
will either prove the sceptics wrong or show that the 鈥渟ightings鈥� are just a
pile of鈥�you know. Either way, analysing the DNA found in faeces is likely to
become an essential tool for every biologist who studies elusive or endangered
animals.

Alec Jeffreys of Leicester University, who invented DNA fingerprinting, has
volunteered to do a DNA analysis of any faeces connected with a beast sighting.
鈥淚 have a holiday home on the edge of the Bodmin Moor,鈥� he explains. 鈥淚f I pull
this off, I may be able to get a few drinks off the locals.鈥�

So far, volunteer collectors have sent him two samples. The first came last
November, from a man who saw a creature crouching behind a tree where faeces was
found. Jeffreys knew at once that the dung wasn鈥檛 from a big cat. 鈥淚t was a
rather mucky looking herbivorous dropping,鈥� he remembers. But his lab dutifully
performed the analysis. First, they rinsed the faeces with a lysis solution, to
wash cells from the animal鈥檚 innards off its surface and to destroy the cell
membranes, releasing the DNA. They were careful not to disturb the inside of the
faeces, to avoid contaminating the beast鈥檚 cells with DNA from anything (or
anyone?) it had devoured.

Next they searched for DNA sequences characteristic of big cats, using the
polymerase chain reaction (PCR) to copy the extremely small amounts of DNA again
and again until the molecule could be detected by electrophoresis or other
techniques. Biologists have recently identified primers鈥攕hort stretches of
DNA that tell PCR enzymes which DNA strands to copy鈥攆or the distinctive
molecular 鈥渇ingerprints鈥� of exotic animal species ranging from Indian elephants
to dugongs. In the case of the Bodmin Moor faeces, the DNA split about
fifty-fifty between dog and sheep. Jeffreys suspects that the eyewitness really
saw a big black dog leaving his mark on some sheep droppings, and suggests that
the man might want to get a new set of glasses.

Cat scat

The second sample came to the lab this summer and at first seemed more
promising鈥攊t, at least, looked cat-like. But the analyses failed to pick
up any large-cat DNA and, says Jeffreys, the scat was too small to come from a
big cat. 鈥淲hatever he saw, it sure as hell wasn鈥檛 as exciting as a puma or
leopard,鈥� says Jeffreys, who believes it was probably a domestic cat gone wild.
鈥淚 have to say I鈥檓 rather tempted to go down there and mount my own
别虫辫别诲颈迟颈辞苍.鈥�

Other scientists interested in elusive animals are doing just that. 鈥淚t鈥檚
just such an easy resource,鈥� says evolutionary biologist Robert Wayne of the
University of California in Los Angeles, who specialises in recovering DNA from
degraded material such as ancient bones. He has several ongoing faeces projects
in his lab and predicts that within five years the technique will be refined to
the point where 鈥渋t will become part of the standard repertoire to find out
about animals鈥� secret lives鈥�.

The first researchers to work on excremental PCR were actually studying
cancer-related genetic mutations at Johns Hopkins Medical Institutions in
Baltimore. Six years ago, the group published a report in Science (vol
256, p 102) showing that they could detect the mutated gene in stool samples
from patients with colon cancer, providing a noninvasive method to detect
colorectal tumours.

Wildlife biologists read the article and realised how much potential the
technique had for their own work. Hunters have always used the size and shape of
faeces to identify animals鈥攆or instance, rabbits leave piles of little
pellets, while a few huge round dollops might come from a bear. But faecal DNA
analysis promised so much more. Faecal DNA contains evidence about the species
and sex of the animal which left it, and about the animal鈥檚 blood ties to others
in the pack. The DNA of faecal pathogens offers clues to which diseases the
animal had, and by digging deeper into the faeces, you can find out precisely
what the animal has eaten.

Before this type of analysis came along, the options included trapping
animals and drawing blood, a technique riddled with problems because some
animals are just too shy or dangerous too trap, or it鈥檚 illegal. What鈥檚 more,
you can never be sure you have a representative sample of a population.
Researchers who wanted to look at DNA could set up food traps surrounded by
barbed wire to snag animals鈥� hair for analysis, but not all animals are daring
enough to enter a trap.

The turning point in applying the power of PCR to animal faeces came in a
brief letter in Nature in 1992 (vol 359, p 199). Svante P盲盲bo
and his colleagues at the University of Munich, who are best known for their
studies of fossil faeces, described how they had used fresh dung to investigate
a population of European brown bears in the mountainous Brenta region of
northern Italy. Anecdotes from local villagers suggested that only a few bears
remained, but no one knew the precise number. When conservationists set up video
cameras around bear bait, for instance, the films seemed to show only three
different bears, and wildlife officials had started to consider importing more
from the bigger bear communities in the Balkans. To help decide if they should,
the Munich researchers collected bear faeces from the woods. Then they searched
for a gene only found on the Y chromosome, and analysed one small section of DNA
found in the mitochondria, the organelles that provide the cells鈥� energy. Each
cell has hundreds of mitochondria, so its DNA is easier to detect than nuclear
DNA.

Although the Y-chromosome analysis of three different samples showed that the
faeces came from both males and females, so they could still reproduce, the
mitochondrial sequences were identical, hinting that the population was very
small and isolated. And since the mitochondrial sequences were also quite
similar to those found in bears from Slovenia, it was clear that Slovenian bears
would be better for supplementing the Brenta community than bears from Croatia
or Bosnia. After years of deliberation, the Italian authorities have decided to
import bears from Slovenia.

As they worked with bear faeces, the researchers also looked for clues to
what the animals ate. From plant chloroplast genes they worked out that, in late
summer at least, the bears practically live on a Photinia villosa, a
member of the rose family with small white flowers and red berries.

鈥淭hat鈥檚 really where it started, that little note in Nature,鈥� says
Wayne. Yet despite the method鈥檚 obvious potential, most wildlife biologists had
little experience with PCR, and many technical obstacles had to be overcome
before such faecal analysis caught on.

鈥淭here鈥檚 definitely tweaking that you have to do with the method,鈥� says
biologist Samuel Wasser of the University of Washington in Seattle. 鈥淭here鈥檚 a
lot of stuff in there that you have to get out.鈥� Since faeces contain substances
that make it hard to copy DNA鈥攁mong them plant sugars, digestive enzymes,
mucus and bile salts鈥攖he results improved when researchers used
DNA-adsorbing beads to get the molecule out of particularly mucky samples. And
as always with PCR, the results could mislead if the primers weren鈥檛 specific
enough or if contamination occurred (This Week, 15 August, p 19). In one study,
primers for baboon DNA picked up genetic material from the baboons鈥� human
cousins鈥攗ntil lab workers improved the specificity of their primers.

Even after that refinement, researchers were sometimes surprised to see three
copies of a gene in the baboon faeces when there should have been only two. The
contamination was caused when grooming animals swallowed each others鈥� hair.
Researchers solved the problem by swapping to extraction techniques which could
not digest hair cells.

With many of the problems now sorted out, Michael Kohn, who worked on the
Brenta bear study, has pitted faeces analysis against the old ways of studying
animal populations. Based at Wayne鈥檚 Los Angeles lab, he has been taking trips
out in the Santa Monica mountains to collect several hundred samples of coyote
faeces. Years of trapping the animals and tagging them with radio collars gave
him the data he needed to do the comparison.

When Kohn collected faeces in an area thought to be inhabited by 11 or 12
coyotes, he found instead evidence of about 40 coyotes. 鈥淭his makes this
technique very powerful for a census. The fascinating thing is that it went so
fast,鈥� says Kohn. 鈥淭he collection took two weeks, the analysis took around four
months, and it鈥檚 very cheap.鈥� Trapping and tagging animals, in contrast, can
take years.

That鈥檚 not to say that faeces collection doesn鈥檛 present challenges of its
own. Many animals don鈥檛 leave their mark on hiking trails, and finding faeces in
the forest can be like looking for a needle in a haystack. Wasser realised that
this would be a serious problem when he sat down to plan a study of grizzly
bears, endangered lynx and recently introduced wolves in Wyoming鈥檚 enormous
Yellowstone National Park. Then inspiration struck, and he called the state鈥檚
Department of Corrections to see if they might spare a few drug-sniffing dogs.
Wasser鈥檚 team joined the dogs and their trainers at a medium-security prison on
McNeil Island near Seattle, and taught them the scent of different species鈥�
faeces rather than cocaine or marijuana.

By bringing samples to the island and hiding them in the woods, the
researchers could get a sense of how well the dogs performed. 鈥淭he dogs can
detect a sample half a mile away and can do up to 19 species at once,鈥� says
Wasser. In 30 minutes they can collect all the scat in a 40 000-square-metre
search grid.

Using dogs also eliminates any bias that might occur when researchers collect
faeces along trails, or when they collect hairs in the barbed wire of baited
traps. 鈥淔aeces are used as a signal. Some animals want to be more conspicuous
than others,鈥� says Wasser. So faeces on trails might come from only a certain
segment of the animal population, while hair traps might only appeal to the most
aggressive or adventurous animals. 鈥淭he dog is the Cadillac way of dealing with
these selection biases,鈥� says Wasser, who plans to have five dogs combing the
woods of Yellowstone National Park this summer.

One mystery has already been solved by Wasser鈥檚 DNA analysis of faeces. In
Washington state, bears often kill trees by stripping off their bark for food.
Timber companies have put out millions of kilograms of food in an unsuccessful
effort to lure the bears away from trees. By collecting faeces from around
stripped trees and feeding centres, Wasser showed that more than 70 per cent of
the animals peeling bark were female, while most of those which visited the
feeding station were male. The males were getting a free meal from the timber
industry while for the females it was business as usual.

Wasser is also hoping to use faeces to combat ivory poaching. When the ivory
trade was in its heyday, so many elephants were illegally poached that they were
nearly wiped out in some parts of Africa. In 1989, the UN Convention on
International Trade in Endangered Species put a worldwide ban on trade in
elephant parts, robbing some countries of valuable export revenue. Now, Wasser
and his colleagues have received a grant to collect elephant faeces from all
over Africa and build a database of elephant DNA fingerprints and where faeces
were found. If the ban on ivory imports is ever lifted, as some African nations
hope, the data base should make it easier to police the trade.

Meanwhile, Wayne and his colleagues have been studying鈥攐r rather set
out to study鈥攁n endangered species called Darwin鈥檚 fox. The fox normally
lives on Chiloe island, off the coast of Chile, but since some observers claimed
to have spotted it on the mainland, the team began collecting faeces there to
see what they鈥檇 find. In two years, Wayne鈥檚 lab has processed hundreds of
samples, all supposedly from the fox. Almost all turned out to be from a
secretive wildcat called the codcod previously unknown in that part of Chile,
extending the cat鈥檚 known range by a huge amount.

Wildlife researchers have yet to fully exploit the DNA found in faeces.
鈥淭here have been a lot of questions in wildlife conservation that have been
impossible to answer until now,鈥� says Wasser. For example, scatologic DNA
analysis makes it possible to count endangered animals such as Siberian tigers,
or to work out whether leopards still roam Turkey.

But if most people are interested in putting dung DNA to work in the field of
conservation, some have other ideas. On a recent visit to a bookstore, Kohn was
thumbing through a book about Bigfoot. To his surprise, he found a reference to
his Nature paper and the suggestion that faeces could finally prove the
existence of Bigfoot. And P盲盲bo says that a few weeks ago a German
magazine sent him some Abominable Snowman dung. It actually turned out to be fox
scat. Meanwhile, back at Leicester University, Cornish dung samples will keep
coming in, and Jeffreys and his lab will keep analysing them. After all, they
could hold the secret of the beast of Bodmin Moor.