NEW YORK — Researchers have homed in on genetic changes that underpin the various behaviors exhibited by different dog breeds.
Humans have bred dogs for a range of tasks — such as herding or protecting livestock, killing vermin, and hunting — giving rise, for instance, to sheep dogs, terriers, and hounds. But uncovering genes behind dog behavior has historically been challenging, according to study first author Emily Dutrow, a postdoctoral fellow at the National Human Genome Research Institute.
"The inherent complexity of canine population dynamics features varying degrees of selective pressure for aesthetic and morphological traits, some of which may be linked to behavioral traits, so pinpointing the genetics of canine behavior can be complicated," Dutrow said in a statement.
Using DNA samples from more than 4,000 domestic, semi-feral, and wild dogs in tandem with behavioral survey data for more than 46,000 dogs, Dutrow and her colleagues from NHGRI and the University of Pennsylvania homed in on genes associated with certain breed-linked behaviors like herding. As they reported on Thursday in the journal Cell, the researchers found that variants associated with sheep dogs were often near genes involved in ephrin signaling, which is involved in brain development, and hint at how they could influence behavior.
With whole-genome sequencing or SNP array data on 2,823 purebred dogs, 687 mixed-breed pet dogs, 658 semi-feral village dogs from 47 countries, and 93 wild canids from four continents, the researchers first examined the genetic relationships between the dogs, which separated them into 10 major lineages. These lineages largely correlated, the researchers found, with the tasks for which the dogs were originally bred, indicating that similar genes were responsible for behaviors across dogs developed for similar roles.
Using their survey data from the owners of purebred dogs, the researchers then developed breed-average behavioral metrics. This found, for instance, that terriers tended to exhibit predatory behaviors, while sheep and cattle dogs were more trainable, though energetic. These behaviors were likewise correlated with the genetic divergence along the breed lineages.
Through genome-wide association studies, the researchers identified the top 100 loci associated with each breed lineage. As the researchers noted, these variants were not lineage-specific and were found at moderate allele frequencies across their entire cohort. This suggested to them that breed diversification was driven by variation that already existed among dogs.
Further, of the 16,250 variants significantly associated with the lineages analyzed, only a small number, 76, were coding variants predicted to have a moderate or high impact, pointing to a role for regulatory variation in breed development.
The researchers were particularly interested in livestock herding dogs, as their eponymous behavior is complex, requiring both the instinct to herd and the motor patterns to shuffle livestock around in intricate ways. Within sheep dogs, the researchers uncovered an enrichment of genes involved in axon guidance.
Additionally, a number of sheep dog-linked variants were found near genes associated with ephrin signaling, which is also involved in brain development and behavior. In particular, the researchers noted that a sheep dog-linked locus near the axon guidance gene EPHA5, which encodes an ephrin receptor, has also been tied to attention-deficit hyperactivity disorder in humans and anxious behaviors in other mammals. This could, the researchers said, help explain both the hyper-focus sheep dogs have when given a task as well as their high energy.
"The same pathways involved in human neurodiversity are implicated in behavioral differences among dog lineages, indicating that the same genetic toolkit may be used in humans and dogs alike," Dutrow added.