Tag Archives: DNA

New twist in tale of dogs’ origins

The origin of dogs has inspired a lingering controversy in academia. Where and when did dogs first split off from wolves? One of the top dogs in this dispute, population genetics expert Peter Savolainen of Sweden’s KTH Royal Institute of Technology, isn’t about to roll over. He hopes his latest research will finally settle the matter.

Some researchers say canines first split off from wolves in the Middle East; others say it happened in Europe. But Savolainen has long held that dogs originated in South East Asia alone, and he says his team has compiled new evidence that confirms his earlier findings.

The study concludes that the split with wolves occurred about 33,000 years ago.

Savolainen’s earlier studies were based on analysis of mitochondrial DNA. But recently other researchers have used data from nuclear DNA to refute those findings, arguing that dogs originated in the Middle East, Central Asia or Europe.

But apparently, those researchers were thrown off the scent, according to Savolainen. The data they relied on did not include samples from South East Asia, he says. So if, as Savolainen says, dogs did indeed come from South East Asia, these studies would not have been able to detect it.

Photo by IStock

Photo by IStock

“Which is why we analysed the entire nuclear genome of a global sample collection from 46 dogs, which includes samples from southern China and South East Asia,” he says. “We then found out that dogs from South East Asia stand out from all other dog populations, because they have the highest genetic diversity and are genetically closest to the wolf.”

Savolainen says this provides strong evidence that the dog originated in South East Asia, which confirms his earlier studies of Mitochondrial DNA.

“We also found that the global dog population is based on two important events: the dog and wolf populations first began to split off about 33,000 years ago in South East Asia. The global spread of dogs followed about 18,000 years later.

He says one explanation for the split between dogs and wolves 33,000 years ago could be that the wolf population became divided and the south Chinese wolf developed into dogs. In that case, it is possible the global spread of dogs out of South East Asia is associated with domestication.

“The dog’s story thus appears to have begun 33,000 years ago, but the exact path to the fully-domesticated dogs that spread throughout the world 15,000 years ago is not yet clear,”

Savolainen, along with 14 other scientists, recently published the scientific article “Out of Southern East Asia: The Natural History of domestic dogs across the world.

Source:  AlphaGalileo media release

A bond that goes way back

The special relationship between humans and dogs may go back 27,000 to 40,000 years, according to genomic analysis of an ancient Taimyr wolf bone reported in the Cell Press journal Current Biology on May 21. Earlier genome-based estimates have suggested that the ancestors of modern-day dogs diverged from wolves no more than 16,000 years ago, after the last Ice Age.

The genome from this ancient specimen, which has been radiocarbon dated to 35,000 years ago, reveals that the Taimyr wolf represents the most recent common ancestor of modern wolves and dogs.

his image compares an ancient Taimyr Wolf bone from the lower jaw to a modern pipette.  Photo by Love Dalén

This image compares an ancient Taimyr Wolf bone from the lower jaw to a modern pipette. Photo by Love Dalén

“Dogs may have been domesticated much earlier than is generally believed,” says Love Dalén of the Swedish Museum of Natural History. “The only other explanation is that there was a major divergence between two wolf populations at that time, and one of these populations subsequently gave rise to all modern wolves.” Dalén considers this second explanation less likely, since it would require that the second wolf population subsequently became extinct in the wild.

“It is [still] possible that a population of wolves remained relatively untamed but tracked human groups to a large degree, for a long time,” adds first author of the study Pontus Skoglund of Harvard Medical School and the Broad Institute.

The researchers made these discoveries based on a small piece of bone picked up during an expedition to the Taimyr Peninsula in Siberia. Initially, they didn’t realize the bone fragment came from a wolf at all; this was only determined using a genetic test back in the laboratory. But wolves are common on the Taimyr Peninsula, and the bone could have easily belonged to a modern-day wolf. On a hunch, the researchers decided to radiocarbon date the bone anyway. It was only then that they realized what they had: a 35,000-year-old bone from an ancient Taimyr wolf.

The DNA evidence also shows that modern-day Siberian Huskies and Greenland sled dogs share an unusually large number of genes with the ancient Taimyr wolf.

“The power of DNA can provide direct evidence that a Siberian Husky you see walking down the street shares ancestry with a wolf that roamed Northern Siberia 35,000 years ago,” Skoglund says. To put that in perspective, “this wolf lived just a few thousand years after Neandertals disappeared from Europe and modern humans started populating Europe and Asia.”

Source:  EurekAlert! media statement

The ancestral roots of your dog

A genetic study by Peter Savolainen, a researcher in evolutionary genetics at KTH Royal Institute of Technology in Stockholm, has found that dog breeds from North and South America have Asian ancestry.

The Chihuahua definitely has Mexican heritage

The Chihuahua definitely has Mexican heritage

The native breeds have 30 percent or less modern replacement by European dogs.  It had been thought, prior to this study, that when Europeans settled in the American continent their dog breeds successively replaced the genetics of the native breeds.

Savolainen’s research group, in cooperation with colleagues in Portugal, compared mitochondrial DNA from Asian and European dogs, ancient American archaeological samples, and American dog breeds, including Chihuahuas, Peruvian hairless dogs and Arctic sled dogs.

They traced the American dogs’ ancestry back to East Asian and Siberian dogs, and also found direct relations between ancient American dogs and modern breeds.

The research confirmed conclusively that the modern day Chihuahua has Mexican roots.  The breed shares a DNA type uniquely with Mexican pre-Columbian samples.

The team also analysed stray dogs, confirming them generally to be runaway European dogs; but in Mexico and Bolivia they identified populations with high proportions of indigenous ancestry.

Source:  AlphaGalileo Foundation news release

Researchers identify gene associated with eczema in dogs

A novel gene associated with canine atopic dermatitis has been identified by a team of researchers led by professors Kerstin Lindblad-Toh, Uppsala University and Åke Hedhammar, SLU, Sweden. The gene encodes a protein called plakophilin 2, which is crucial for the formation and proper functioning of the skin structure, suggesting an aberrant skin barrier as a potential risk factor for atopic dermatitis.

Details appear in the open-access journal PLoS Genetics.

Atopic dermatitis (or eczema) is an inflammatory, relapsing non-contagious skin disease affecting about 3-10 percent of dogs. The skin of a patient with atopic dermatitis becomes easily irritated by various allergens such as certain types of food, pollens or house mites. Such irritation causes very strong itching which leads to scratching, redness and flaky skin that becomes vulnerable to bacterial and yeast infections.

Despite many scientific efforts, little has been known about the genetics of the disease. In their study, researchers from Uppsala University, SLU and Broad Institute, compared DNA samples from a large group of German shepherd dogs affected by atopic dermatitis with DNA coming from healthy dogs to reveal the specific DNA segment associated with the disease.

“With the help of pet owners, we have managed to collect a unique set of DNA samples from sick and healthy dogs which allowed us to gain insight into atopic dermatitis genetics,” said first author Katarina Tengvall, Uppsala University.

Purebred dogs such as German shepherds have been selected for specific physical features for several generations. Selection led to an inadvertent enrichment for disease-risk genes in certain breeds. Moreover, the resulting architecture of canine DNA makes it easier to pinpoint segments that carry these disease risk-genes. This helped the researchers to reveal the genetics of atopic dermatitis. They found a region associated with the atopic dermatitis containing the gene PKP-2, which encodes Plakophilin-2, a protein involved in the formation and maintaining of the proper skin structure.

“The finding that certain variants of the PKP-2 gene may increase the risk of developing the disease opens new possibilities in understanding the disease mechanism leading to atopic dermatitis,” continues Katarina Tengvall.

These findings will not only lead to better understanding of the disease, which may lead to better treatment strategies long term. It also opens up the possibilities of development of a genetic test for the disease.

“Our study suggests that plakophilin-2 and an intact skin barrier is important to avoid atopic dermatitis”, says senior author, Kerstin Lindblad-Toh, professor at Uppsala University and Director of SciLifeLab Uppsala. “Another gene involved in the skin barrier has recently been linked to human atopic dermatitis emphasizing the similarity between canine and human atopic dermatitis” said Kerstin Lindblad-Toh.

Source:  AlphaGalileo Foundation media statement

Re-thinking dog domestication

A research team led by the University of Durham has published a study in the Proceedings of the National Academy of Sciences (USA).  This study shows that today’s modern breeds of dog have little in common genetically with their ancient ancestors. 

Dog domestication occurred over 15,000 years ago – and there is still much to learn!

Years of cross-breeding are the major influence on the genetic differences, although the researchers are quick to add that other effects on genetic diversity will include patterns of human movement and the impact on dog population sizes caused by major events such as World War I and World War II.

The research team analysed genetic data from 1,375 dogs representing 35 breeds. They also looked at data showing genetic samples of wolves because other research studies have concluded that the dog descended directly from the gray wolf.

Lead author Dr Greger Larson, an evolutionary biologist, says the study demonstrated just how much there is still to understand about the early history of dog domestication.  “We really love our dogs and they have accompanied us across every continent.  Ironically, the ubiquity of dogs combined with their deep history has obscured their origins and made it difficult for us to know how dogs became man’s best friend.”

The study also refutes claims of previous researchers that genetic differences in breeds such as the Basenji, Saluki and Dingo were evidence of an ancient heritage.  The Durham team’s study shows that these dogs are genetically different because they were geographically isolated and were not part of the 19th Century Victorian-initiated kennel clubs that blended lineages to create most of today’s breeds.

A Saluki (copyright Keith Dobney)

Source:  University of Durham press release

CSI – dog style?

Pooprints, based in Tennessee (USA), is offering DNA testing of a different kind.  It is not about testing your mixed breed dog to find out their lineage, it’s about DNA testing of dog poo!

The number of subdivisions, condominium-style accommodation developments, and apartment complexes is on the rise in the US.  This is a result of a ‘downsizing’ of accommodation because of the economic recession as well as growth in population centres where work is available, but cost of living and commuting times are also an issue.  In these types of developments, there are dog owners living alongside non-dog owners.  And poop is  a problem.

(For my New Zealand readers, read my Last Word column in the March 2011 issue of NZ Dog World magazine.  In that column, I discussed the looming liability of infill housing, population growth,  and the growing problem of dog owners who do not clean up after their dog.)

The company’s service is rather straightforward.  First, a residential community decides to start a dog DNA testing programme.  Usually, this test is mandatory as part of signing up to live there. A mouth swab is taken of your dog and sent for  DNA testing and the results are entered into that site’s database.

Then, a site manager is probably responsible for poop patrol in your community.  They take samples of poop that has not been cleaned up and send the samples for DNA testing (because epithelial cells in the wall of the intestine are excreted every time a dog defecates).   The site manager will be given a report about the dog/owner match in order for followup to occur.

Communities will have rules about the number of infringements required for that person to be fined, or worse, kicked out of their residence.

It may sound ‘over the top’ but it is a symptom of how strongly some people feel about poop that is not cleaned up.

CNN covered the story of one residential development in New Hampshire that has signed up to use the Pooprints system.  Read about it here.