DNA from droppings is a revelation, says Roger Highfield
FOSSILISED faeces have an intriguing tale to tell. A pile of dung from an extinct sloth has yielded enough DNA to reveal much about the creature's way of life and environment thousands of years ago.
Previous efforts to amplify traces of DNA in these droppings - coprolites - had failed. Now, however, using chemical treatment, scientists have extracted enough DNA to analyse the genetic make up of one "gift" deposited by a ground sloth some 19,000 years ago.
The study has provided an impressive demonstration of how DNA from ancient excrement can be released and analysed to reveal the animal from which it came, its diet and the parasites that infested it. "This adds several new dimensions to the study of ancient animals," said one evolutionary biologist.
This advance in "molecular coproscopy", which has the potential to work on deposits made up to 100,000 years ago, was described recently in the journal Science by Prof Richard Evershed of Bristol University, working with colleagues in Germany and Sweden.
"This is the first time it has been done on ancient dung," said co-author Dr Hendrik Poinar of the University of Munich, where he carried out the dung project with Prof Svante Pääbo. "This is not Jurassic Park. It's more like 'Poop Park'. From an ancient bone you get an ancient DNA sequence of an animal but from ancient dung you get the sequence of the animal, the sequence of the things he ate, the parasites that infected him. From the diet you can tell what the environment was thousands of years ago."
The coprolites used for the analysis were found in the Gypsum Cave east of Las Vegas, a gathering place for ice age animals. They had been thought to come from a long-extinct ground sloth, Nothrotheriops shastensis, bones of which were found nearby.
Using a technique called polymerase chain reaction, which quickly and efficiently makes trillions of copies of gene fragments, the team amplified exceedingly small samples of DNA for study.
Previous attempts to use the technique had failed but this time the team first mixed the dung with a chemical agent called PTB (for N-phenacylthiazolium bromide), a substance that is known to cleave the bonds between sugars and proteins, the same kinds of bonds that may entangle DNA in dung.
PTB-boosted dung samples pumped out enough DNA for analysis. The authors confirmed the identity of the animal by comparing the DNA, presumably shed from intestinal cells, to that of living tree sloths and ground sloth bones that had been analysed by a team from the Imperial Cancer Research Fund, South Mimms.
Significantly, the analysis also revealed the presence of seven different kinds of plants in the sloth's diet, from capers and mustards to lilies, grasses, borages and mints.
Some plants that formed part of the sloth's diet still exist today at elevations about 800 metres higher than the cave. One of the plants appears to have been from the grape family. The only representative of this family in the Mojave Desert today is the wild grape, which occurs around springs and streams.
Sources of water near the cave at that time may have been as far away as 20km, suggesting that the sloth, which was as big as a pony, may have travelled substantial distances to eat and drink.
From caves in Gibraltar and in Spain, Dr Poinar said there are coprolites that may have come from Neanderthals, an ancient relative of humans. Last year his colleague Prof Pääbo solved a long and acrimonious dispute about whether we are related to Neanderthal man - an argument hitherto conducted by comparing bone shapes.
He extracted 30,000-year-old Neanderthal DNA and provided convincing evidence that we are not descendants of the Neanderthals. Now he is analysing samples of what could be Neanderthal faeces from 45,000-year-old cave deposits in Gibraltar.
The droppings could reveal what Neanderthals ate and what parasites tormented them. They could help scientists understand how the Neanderthals migrated across Europe. And they will shed new light on their kinship with our own species. "I am gathering as much poop as I can," Dr Poinar said.
