Dogs are now part of society, not just as domesticated animals, but as part of family. They are known for their deep loyalty and are fondly called "man's best friend."
Previous studies had focused on the evolution of domesticated dogs. In one study, it was suggested that 70,000 years ago, the early humans in Europe started domesticating wolves and breeding dogs from domesticated wolves to help them vanquish their Neanderthal rivals. DNA analysis in another study proved that domesticated dogs have been around for at least 33,000 years. The DNA study also found that primitive dogs from Southeast Asia are closely related to gray wolves.
But no matter when or from where dogs were domesticated, the whole process of domestication might have caused detrimental effects on the dogs' genetic makeup, according to a new study.
Researchers from the University of California, Los Angeles (UCLA) said that while inbreeding and artificial selection were involved in the dogs' domestication, the effects of these processes on the dogs' genes have not been studied comprehensively. For this reason, the team sought to find out the effects and identify which aspects of domestication may have led to an increased number of harmful genetic changes in dogs.
The researchers analyzed the complete genome sequences in a total of 90 canids: 46 domesticated dogs from 34 breeds, 19 gray wolves and 25 village dogs from 10 various countries.
The researchers found that bottlenecks, or the reduction in population size, and selective sweeps, or the reduction in the DNA's nucleotide variation, during domestication have increased the harmful genetic changes in dogs.
"Population bottlenecks tied to domestication, rather than recent inbreeding, likely led to an increased frequency of deleterious genetic variations in dogs," said Kirk Lohmueller, senior author of the study and assistant professor of ecology and evolutionary biology at UCLA.
The researchers say that the domestication of gray wolves to become dogs may have resulted in an increased number of genetic variations that could lead to a number of health risks and different developmental disorders in dogs.
The researchers explained that when dogs were artificially bred in small populations for desired traits such as fur type, coat color or body size, the process changes the dogs' genetic makeup. However, while selective breeding may have given humans the perfect pet, it also made dogs susceptible to hereditary diseases because it also carried over disease-related genes.
The results of the study also have implications for selective breeding programs, particularly those geared toward the conservation of endangered species. To avoid unintentionally building up the harmful genetic variants among the animals they are trying to save, conservationists would need to include more animals in their programs as much as possible.
"Our results also suggest that maintaining a large population size, rather than just avoiding inbreeding, is a critical factor for preventing the accumulation of deleterious variants," the researchers wrote [pdf] in their study.
The study also provides an estimate of the increased burden of harmful variants directly linked to domestication, which wildlife conservationists can use to improve their programs.
"Our approach provides a comprehensive method for evaluating deleterious variation from genome data in the small isolated and threatened populations worldwide that can help prioritize their genetic management," the researchers said.
Photo: Aleksey Gnilenkov | Flickr
