Wednesday, April 27, 2016
Tuesday, September 27, 2005
Monday, September 26, 2005
Sunday, September 25, 2005
Tuesday, September 20, 2005
The tactic helps bind families without the dangers of inbreeding
This serves to bind families together, but avoids the dangers of inbreeding.
The females live together in groups segregated from the opposite sex, but gang together to prowl for males once the mating season arrives.
Scientists from the University of Bristol and Queen Mary in London made the discovery using genetic techniques to construct family trees for the bats.
Most female greater horseshoe bats (Rhinolophus ferrumequinum) seek out the same male to mate with year after year.
The bats produce only one offspring each year, so each animal represents the outcome of a separate mating.
Stephen Rossiter, of Queen Mary, University of London, and colleagues used genetic typing to compile the family trees of some 452 bats at Woodchester Mansion in Gloucestershire, UK.
The researchers mapped male partners on to pedigrees of female bats to examine patterns of pairings down the years.
They found that relatives on the maternal line shared male partners more often than would be expected by chance.
In all, they detected 20 groups of related females sharing mates, with two to five individuals in each of these groups.
Dr Rossiter believes that by sharing sexual partners, the greater horseshoe bat "strengthens social ties and promotes greater levels of cooperation within the colony".
It pays to share
Kinship between individual animals is extremely important for cooperation and, therefore, social cohesion, says Dr Rossiter and his team.
The tendency for females to return to the same males each year also strengthens this kinship.
Any behaviour, such as this, which increases the levels of relatedness within social groups while dodging the costs of inbreeding is likely to be favoured by natural selection, the researchers write.
In the UK, greater horseshoe bats are thought to have declined by 90% over the past 100 years.
This may be due to the disturbance of roosts and changing farming practices, since the use of pesticides has caused a declined in the insects they prey on.
Monday, September 19, 2005
Scientists in Israel have just developed a new technique to retrieve better quality, less contaminated DNA from very old remains, including human bones.
It could aid the study of the evolution and migration of early modern humans, as well as extinct populations such as our close relatives, the Neanderthals.
Many researchers would dearly love to get their hands on DNA samples from hominids further back in time - from those that lived 100,000 years ago or more - to find out how they were related to people alive today.
But fossil studies this far back in time have long been hindered by contamination with foreign genetic material and the problem of recovering long, intact DNA sequences.
The new method provides hope, however.
"DNA gets everywhere. So when we're dealing with a sample and you find it's got human DNA in it - is that DNA from the fossil, or is it actually DNA from the person who unearthed it?" says Professor Chris Stringer, the head of human origins at the Natural History Museum in London, UK.
"It breaks up into very small fragments so it is quite technically complicated to put it all back together again," explains Dr Robert Foley, the director of the Leverhulme Centre for Human Evolutionary Studies at the University of Cambridge, UK.
Freezing provides the ideal preservation conditions. The most widely accepted oldest DNA yet isolated comes from 400,000-year-old plants found in ice in Siberia. But most specimens are not excavated from such places.
An improved technique for retrieving DNA from fossil bone, just published in the journal Proceedings of the National Academy of Sciences (PNAS), may help.
Dr Michal Salamon, from the Weizmann Institute of Science in Rehovot, Israel, and colleagues, showed that "crystal aggregates", small mineral pockets formed during fossilisation, can preserve DNA better than the rest of the bone.
They compared DNA extracted from these crystal aggregates with genetic material taken from untreated, whole-bone powder. The samples were taken from eight different modern and fossil bones.
This approach, "significantly improves the chances of obtaining authentic ancient DNA sequences, especially from human bones", they told PNAS.
Commenting on the latest research, Dr Michael Hofreiter, from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who helped decode 40,000-year-old nuclear DNA from a cave bear earlier this year, said: "It's possible; but there need to be more studies on more samples, and they need to show that you don't get human contamination of animal bones.
"Then I would believe that it is a breakthrough for ancient DNA research."
The big split
Scientists are hopeful the new technique will help them get at the DNA in the chromosomes of a cell - the nuclear DNA.
Ancient DNA research has so far mainly focused on mitochondria, the tiny "power-stations" of the cell. These exist outside of the nucleus and have their own DNA. And, although this information is very useful, it is more limited in its scope than that which could be obtained from nuclear DNA.
"There's about 1,000 times more mitochondrial DNA than nuclear DNA in our cells, so it's much easier to pick up," explains Professor Stringer.
The mitochondrial DNA is inherited only through the egg - through females. This means it is a useful marker for tracing a line back into the past, as it has never been mixed with DNA from males.
"One of the most important discoveries from studying ancient mitochondrial DNA is the estimate of when humans diverged in evolution from the Neanderthals - around half a million years ago," according to Dr Foley.
Professor Stringer adds: "We've now got about 10 Neanderthal specimens of around 40-50,000 years old that have yielded DNA that is clearly distinct from anyone alive today."
This means scientists can be sure that it is ancient, not just modern DNA from contamination.
It has also given them a measure of how different Neanderthals were from modern people.
"Neanderthals are three times as different from us as we all are from each other," says Professor Stringer.
But there remains the hotly debated question of whether Neanderthals were a completely separate species to us. Professor Stringer says that they are if that assessment is based on studying their bone anatomy.
However, the evidence from mitochondrial DNA is somewhat ambiguous.
"The mitochondrial DNA on its own can't tell us if we're a distinct species," he explains.
"It depends what mammal you take. There are some species where the difference in mitochondrial DNA between us and Neanderthals would say they were a different species.
"Whereas in chimpanzees, our closest relative, you could contain the variation between us and Neanderthals in a single species alive today in Africa."
Scientists need to recover better DNA from our fossils, especially the nuclear DNA.
"Each gene has a separate evolution so to understand Neanderthals properly we will need different bits of their DNA to see if they're all telling us the same story," he adds.
The male sex chromosome (the "Y") is useful for tracking male inheritance, since males inherit their Y chromosome only from their father.
Using both mitochondrial and Y chromosome DNA from people alive today, complex pathways have been mapped for how modern humans got to where they are - but there are problems.
Dr Mim Bower, an ancient DNA researcher at the McDonald Institute for Archaeological Research in Cambridge, UK, gives an example.
"Using modern DNA we see a different pattern of settlement in the Pacific islands between men and women - the mitochondrial DNA patterns show a different migration pattern to the Y chromosome DNA."
Studying the DNA not of modern humans but of their distant ancestors could help answer such questions.
"At the moment we can't follow that into the past as it's very difficult to get nuclear DNA," Dr Bower says.
This is especially problematic for the Y chromosome, which is nuclear.
Source: The Genographic Project