In Divergence From Wolves, Doggie Diet Made A Difference

Composite image by Lauren Solomon, courtesy of Broad Institute;
dog image @ iStockphoto/Nicholas Moore

“I think it’s intuitive, cool, and exciting: what you eat is very different if you are a domesticated dog rather than a wolf, and that could have a lot to do with domestication,” said Kerstin Lindblad-Toh, a professor in comparative genomics at Uppsala University, the director of Science for Life Laboratory Uppsala, and the scientific director of vertebrate genome biology at the Broad Institute. “While it certainly doesn’t prove how dog domestication happened, these signatures of selection strongly suggest that food source was a key driver in the domestication of dogs. One could speculate that dogs may very well have domesticated themselves, drawn to the scrap heaps left by human beings as people’s diets began to change when agriculture emerged.”

In a paper published this week in Nature, Lindblad-Toh and her colleagues describe the results of looking across the full genomes of dogs and wolves to pinpoint regions that separate the two species. The researchers used two, unbiased approaches to find telltale signs of evolution, narrowing in on 36 regions that likely represent targets of selection during dog domestication.

Half of these regions harbor genes tied to brain development or signal processing that occurs in the brain. The researchers also identified ten genes in other genetic regions that play key roles in the digestion and metabolism of starches and fats. Lindblad-Toh and her colleagues are continuing to follow up on the genes tied to the brain, especially nervous system development. Meanwhile, they have put the genes tied to digestion to the test, determining that all three genes governing the three major steps of the breakdown of complex starches are used more effectively in dogs.

“While many processes in our body are complicated, sugar metabolism, although not simple, can be broken down into three, clear steps: the body uses amylase, then maltase, to break down food, and then absorbs sugar in the gut,” said Lindblad-Toh. “Here, we’ve demonstrated really strong signatures of selection at each of those steps. It’s clear that making the entire process of sugar uptake better had a major effect during dog domestication.”

In the Nature paper, the authors discuss how this important adaptation – the ability to thrive on a starch-rich diet – may have helped dogs fill a new niche. As human beings transitioned from a nomadic lifestyle to one based around agriculture and settlements, dogs may have been drawn to scrap heaps where humans threw out their garbage. Animals that could scavenge these piles may have had a unique advantage over others – an advantage that would have drawn them into close contact with people.