Diet Shaped Dog Domestication

Fido may prefer steak, but his digestive system is also geared up for rice and potatoes. That's the conclusion of a new study, which finds that dogs have evolved to eat a more varied diet than their wolf ancestors. The shift parallels genetic changes seen in people and bolsters the idea that dogs and humans share similar evolutionary stories.

Dogs evolved from wolves more than 11,000 years ago, somewhere in Eurasia, though exactly when and how is under debate. The shift from wolf pack member to family pet involved more than just the ability to get along with people, says evolutionary geneticist Erik Axelsson from Uppsala University in Sweden. He and his colleagues compared dog and wolf DNA to learn which genes were important for domestication.

They sequenced DNA from 12 wolves from around the world and from 60 dogs belonging to 14 breeds. They first looked for individual letters in DNA, called bases, that varied from one genome to the next, identifying about 4 million of these so-called single-nucleotide polymorphisms (SNPs). They ignored regions with the most SNPs and instead focused on places where there were very few or no SNPs. That lack of variation signals DNA that was so important for survival during domestication that any variation there was lost, so most dogs have the same SNPs. Those regions were the ones the researchers were most interested in following up on.

The analysis turned up 36 regions, with 122 genes in all, that may have contributed to dog evolution, the team reports online today in Nature. Nineteen of these regions contain genes important for the brain, eight of which are involved with nervous system development, which makes sense given the importance of behavioral changes in the transition to becoming man's best friend, Axelsson notes.

More surprising were genes for digesting starch. Dogs had four to 30 copies of the gene for amylase, a protein that starts the breakdown of starch in the intestine. Wolves have only two copies, one on each chromosome. As a result, that gene was 28-fold more active in dogs, the researchers found. More copies means more protein, and test-tube studies indicate that dogs should be fivefold better than wolves at digesting starch, the chief nutrient in agricultural grains such as wheat and rice. The number of copies of this gene also varies in people: Those eating high carbohydrate diets -- such as the Japanese and European Americans -- have more copies than people with starch-poor diets, such as the Mbuti in Africa. "We have adapted in a very similar way to the dramatic changes that happened when agriculture was developed," Axelsson says.

Dogs and wolves have the same number of copies of another gene, MGAM, which codes for maltase, another enzyme important in starch digestion. But there are four key differences between the sequence in dogs and wolves. One difference causes dogs to produce longer versions of maltase. That longer protein is also seen in herbivores, such as cows and rabbits, and omnivores, such as mouse lemurs and rats, but not in other mammals, suggesting length is important to plant-eaters. These differences make the dog maltase more efficient, the researchers report.

Axelsson thinks these results support the idea that wolves began to associate with humans who were beginning to settle down and farm. Waste dumps provided a ready source of food, albeit not meat, the usual diet. Thus early dogs that evolved more efficient starch digestion had an advantage, he notes.

The finding of these diet-related genes is "very surprising and very exciting," says Elaine Ostrander, a geneticist at the National Human Genome Research Institute in Bethesda, Maryland, who was not connected to the study. "It hints that there are a lot more [genes] to be found" involved in domestication, she adds. As more researchers compare wolf and dog DNA, Ostrander expects more genetic differences between dogs and wolves to emerge. "We are really going to figure [dog evolution] out."

Robert Wayne, an evolutionary biologist who studies dogs at the University of California, Los Angeles, but was not involved with the work, is also pleased with the study. He says he gets contacted often by pet owners wondering if dogs, like wolves, should eat primarily meat. "This [study] suggests no, dogs are different from wolves and don't need a wolflike diet," he says. "They have coevolved with humans and their diet."
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References:

Pennisi, Elizabeth. 2013. “Diet Shaped Dog Domestication”. Science. Posted: January 23, 2013. Available online: http://news.sciencemag.org/sciencenow/2013/01/dog-domestication-tied-to-starch.html

Jamestown settlers' trash confirms hard times

Analyses of discarded oyster shells chronicle deep drought during Virginia colony’s early years.

Oyster shells excavated from a well in Jamestown, Va., the first permanent British settlement in North America, bolster the notion that the first colonists suffered an unusually deep and long-lasting drought.

The shells reveal that water in the James River near the colony, where many of those oysters were harvested, was much saltier then than along that stretch of the estuary today, says Howard Spero, a geochemist at the University of California, Davis. For the water to have been so brackish, river flow must have been slacker compared to today, a sign that precipitation was dramatically lower when those oysters were growing. Spero and his colleagues report their findings online May 31 in the Proceedings of the National Academy of Sciences.

Jamestown was established in 1607. The early years weren’t easy: Many accounts of Jamestown’s early settlers, including journal entries and letters home, chronicled the drought. So did the region’s trees, Spero says. Previous studies based on tree rings and original documents revealed that the first colonists’ arrival coincided with the beginning of a drought that included the driest seven-year interval in almost 800 years.

“It was interesting trying to figure out what was happening in the colony at a time when 70 to 80 percent of the colonists were dying,” Spero says. “This was ‘CSI Jamestown’.”

Now, oysters independently confirm the tale from trees and historical accounts, comments William M. Kelso, an archaeologist at Preservation Virginia’s Jamestown Rediscovery project who was not involved in the study. “We’re getting a consistent story from science and the humanities,” he notes. “It’s pretty fantastic.”

The telltale oysters were unearthed from a well that sat within the fort at Jamestown, about 100 yards from the river. Among other material dumped into the well, the shells came from three distinct layers up to 3.5 meters deep. The well’s water level originally sat deeper, at a depth of about 4 meters, so Spero and his colleagues suggest that the settlers abandoned the well — which either ran dry during the drought or was infiltrated by salty groundwater — and converted it into a trash pit.

Historical accounts suggest that settlers dug the well sometime between 1609 and 1617, but items unearthed from the well narrow that window considerably, Spero says. For one thing, ratios of different forms, or isotopes, of oxygen in the shells suggest that the mollusks were harvested before the drought ended in late 1612.

One archaeological artifact found beneath the oyster shells, a ceremonial item linked to a particular nobleman from England, couldn’t have been present in Jamestown before he arrived in June 1610 and probably wouldn’t have been discarded in the well until after that nobleman’s return to England in April 1611. That data, plus the pattern of isotope variations in the oyster shells — which reveal the season when those shells were harvested — hint that the mollusks were gathered and eaten between late fall 1611 and summer 1612.

Analyses of the oyster shells have raised another mystery, Spero says. The oxygen-isotope ratios in the middle layer of shells are substantially different from those in the upper and lower layers, which other data suggest were gathered locally. That disparity indicates that the middle oysters, which were shucked in March and April of 1612, were gathered elsewhere, Spero says. Further analyses of trace elements in those shells should reveal whether the oysters were gathered in another part of the James River watershed or were collected elsewhere along the Mid-Atlantic coast and brought to Jamestown by sailors on an English supply ship.
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References:

Perkins, Sid. 2010. "Jamestown settlers' trash confirms hard times". Science News. Posted: May 31, 2010. Available online: http://www.sciencenews.org/view/generic/id/59777/title/Jamestown_settlers_trash_confirms_hard_times