PNAS Special Feature: Genetics of Canine Domestication, Migration, and Behavior
The Genetics of Canine Domestication, Migration, and Behavior Special Feature in the Proceedings of the National Academy of Sciences (PNAS), advances our understanding of how dogs evolved from wolves and how their genomes and behaviors reflect domestication. The articles examine dog–wolf hybridization, revealing both rare and trace gene flow, and explore how genomic tools illuminate inbreeding, ancestry, and ancient admixture, as well as the genetic basis of canine behavior, links to human psychiatric traits, and the evolution of dogs’ mating systems. Collectively, the papers highlight ongoing challenges and collaborations in decoding the genetic, behavioral, and evolutionary complexity of dogs.
Professor Greger Larson (co-editor) says: Dogs are our oldest domestic companion. This collection of 8 papers both significantly advance our understanding of the history of gene flow between wolves and dogs, and explore the genetic basis of dog behaviours. Combined, they answer a host of key questions and provide the foundation for future research into our most integral animal relationship.
Image credit: Jakub Hałun, CC BY-SA 4.0 , via Wikimedia Commons
Published in the Special Feature Dr Scarsbrook's study 'A 120-y time series of genomes reveals the consequences of closed breeding in German Shepherd Dogs', sequenced genomes from historical German Shepherd Dogs to investigate how the genetic diversity of the breed has changed over the last century. Their analysis showed the breed has suffered a progressive loss of genetic diversity over the past 120 years. This can be linked to population declines during the Second World War and the overuse of just a few popular sires.
Like many modern breeds, the German Shepherd Dog is susceptible to heritable disorders. In purebred dogs, some of these diseases have emerged through the loss of genetic diversity and accumulation of harmful mutations – the result of intensive breeding practices. It was previously unknown, however, whether these processes were driven by the initial establishment of these breeds in the late 19th century, or the later phases of breed development in the 20th century.
New genomic analyses conducted by an international team led by scientists at LMU Munich, the University of Oxford, and the National Institutes of Health (NIH) have shed light on this issue. The researchers sequenced the genomes of nine German Shepherd Dogs from the Natural History Museum in Bern, which lived between 1906 and 1993, and compared them against medieval European dogs that predate the establishment of all breeds, as well as representatives from shepherd breeds today.
Their analysis showed that the genetic diversity of historical German Shepherd Dogs in the early 20th century was already much lower than in dogs from the medieval period, reflecting an initial genetic bottleneck related to early breed formation. After 1945, however, the breed experienced repeated bottlenecks throughout the 20th century, first driven by declines in population size in Germany and beyond due to the effects of war, and then as a result of the repeated use of popular sires.
“Our data revealed a massive drop in the genetic diversity of German Shepherds born during the latter half of the 20th century. This decline, which was partly driven by reductions in population size during the Second World War, has almost certainly impacted the breed's overall health” says LMU paleogeneticist Professor Laurent Frantz, one of the principal investigators of the study.
“On top of this, the excessive use of 'popular sires' has caused further genetic bottlenecks,” explains lead author Dr. Lachie Scarsbrook (LMU and University of Oxford). This has not only changed the appearance of the breed through time, but narrowed the gene pool. With their analyses, the researchers were able to demonstrate and date these bottleneck events – for example, the most recent bottleneck seen in European German Shepherd Dogs can be traced to 1967, and coincides with the birthdate of the popular sire "Quanto von der Wienerau".
A symptom of this diversity loss is an increase in the number of long genomic segments in which both chromosome copies are identical, or homozygous, having been inherited from the same dog. The researchers found a spike in these segments in German Shepherd Dogs born after the Second World War, although their pedigrees did not show any recent signs of inbreeding. These high levels of homozygosity likely led to an increased frequency of recessive traits, which require copies on both chromosomes to manifest.
Moreover, hybridization of German Shepherd Dogs and wolves, as happened in the creation of wolfdogs, generally improves genetic diversity only in the short term, as the scientists’ analyses of wolfdogs such as the Saarloos and Czechoslovakian Wolfdog breeds revealed: “To avoid the dilution of wolf ancestry, breeders had to close the gene pool and repeatedly breed related hybrids with each other. This means that any benefits from introducing new genetic diversity, such as the reduction in the number of identical gene segments, were likely to have been short lived,” says Scarsbrook.
“Museum collections allow us to see just how profoundly we've changed the biology of the species we live with”, says Scarsbrook, and he points out that: “Post-war declines in genetic health are unlikely to be exclusive to the German Shepherd Dog, and we plan to confirm this by studying historical specimens from other breeds”.
Looking towards the future, the authors say the most effective strategy to improve the genetic health of the German Shepherd Dog is to incorporate dogs from countries or lines that haven’t undergone the same bottlenecks. This would ensure the dogs can maintain their “purebred” status, while also maximising the breed's health and longevity.
