（image from Asian Scientist）

Asian Scientist (May 14, 2013) – A team of scientists from China have found that the lengthy and intimate association between dogs and humans has resulted in the genomes of both species evolving in parallel over the past 32,000 years.

To study early dog domestication, a team of researchers led by Dr. Guo-Dong Wang and Dr. Ya-Ping Zhang of the Kunming Institute of Zoology sequenced the genomes of four grey wolves from across Eurasia, three indigenous dogs from Southwest China, and three representatives of modern dog breeds. Geneticists believe that indigenous dogs of South China represent the first stage of canine domestication – their genomes may thus hold insights into the transition from wolves to ancestral dogs.

Writing in the journal Nature Communications, the team found that wolves harbored the highest levels of genetic diversity, and modern dog breeds the least, with indigenous Chinese dogs in the middle. The Chinese dogs were also more closely related to wolves than any other native or modern breed surveyed to date, providing evidence for these dogs as the “missing link” in dog domestication.

The researchers put the split between wolves and native Chinese dogs at 32,000 years ago, much earlier than previously thought. The process probably began with wolves scavenging near human populations, a process the researchers call self-domestication.

“The most interesting hypothesis in this research is self-domestication,” said Dr. Zhang. “Under this hypothesis, early wolves might have been domesticated as scavengers that were attracted to live and hunt commensally with humans. With successive adaptive changes, these scavengers became progressively more prone to human custody.”

The researchers found that domestication had imposed a strong selective force on genes involved in digestion and metabolism, probably driven by a switch to an omnivorous diet, and on genes governing neurological processes, most likely due to a need for reduced aggression and increased complex interactions with humans.

Intriguingly, the team found that the human counterparts of a number of these genes, particularly those involved in neurological processes, had also experienced strong selection pressure over time, a reflection of the similar environmental factors experienced by humans and dogs over millennia of close association.

Importantly, many of the overlapping genes are associated with similar diseases in man and his best friend. One gene, SLC6A4, encodes a protein that transports the neurotransmitter serotonin.

“Association studies have found that both the receptor and the downstream metabolite of SLC6A4 are correlated with aggressive behavior and obsessive-compulsive disorder not only in humans, but also in dogs,” said Dr. Zhang, who added that studying the genetic basis of diseases in dogs may help us understand similar diseases in humans.

For the researchers, the tale does not end here. To understand domestication in greater detail, the group plans to study gene expression in the canine digestive system and brain, and to expand its research to diverse breeds of dogs from around the world.

The article can be found at: Wang et al. (2013) The genomics of selection in dogs and the parallel evolution between dogs and humans. (by Shuzhen Sim)

(By Su-Qing Liu)