Humans have bred different lineages of domestic dogs for different tasks such as hunting,
herding, guarding, or companionship. These behavioral differences must be the result
of underlying neural differences, but surprisingly, this topic has gone largely unexplored.
The current study examined whether and how selective breeding by humans has altered
the gross organization of the brain in dogs. We assessed regional volumetric variation
in MRI studies of 62 male and female dogs of 33 breeds. Neuroanatomical variation
is plainly visible across breeds. This variation is distributed nonrandomly across
the brain. A whole-brain, data-driven independent components analysis established
that specific regional subnetworks covary significantly with each other. Variation
in these networks is not simply the result of variation in total brain size, total
body size, or skull shape. Furthermore, the anatomy of these networks correlates significantly
with different behavioral specialization(s) such as sight hunting, scent hunting,
guarding, and companionship. Importantly, a phylogenetic analysis revealed that most
change has occurred in the terminal branches of the dog phylogenetic tree, indicating
strong, recent selection in individual breeds. Together, these results establish that
brain anatomy varies significantly in dogs, likely due to human-applied selection
for behavior. SIGNIFICANCE STATEMENT Dog breeds are known to vary in cognition, temperament,
and behavior, but the neural origins of this variation are unknown. In an MRI-based
analysis, we found that brain anatomy covaries significantly with behavioral specializations
such as sight hunting, scent hunting, guarding, and companionship. Neuroanatomical
variation is not simply driven by brain size, body size, or skull shape, and is focused
in specific networks of regions. Nearly all of the identified variation occurs in
the terminal branches of the dog phylogenetic tree, indicating strong, recent selection
in individual breeds. These results indicate that through selective breeding, humans
have significantly altered the brains of different lineages of domestic dogs in different
ways.