The impact of extreme skull morphology in domestic dogs on cribriform plate shape.

Dog owners are often impressed by their dog's sense of smell. Many of these dogs, however, have skulls that are quite altered from those of their closest canid relatives. Housed within these skulls are essential olfactory structures like the cribriform plate that play a role in olfaction and the transmission of olfactory nerve impulses to the olfactory bulb of the brain. With improvements in CT technology and accessibility, we are now able to digitally reconstruct in 3D cribriform plate morphology and study its variation within and among species. In this study, we CT scanned the skulls of 95 dog specimens from 45 different domestic dog breeds and 12 species of wild canid and compared the shape of the cribriform plate among three main groups: domestic dog breeds, wolf-like canids, and fox-like canids. Despite only recent selective pressure for extreme skull morphology, domestic dogs display much more variation in cribriform plate shape than wild canids, indicating that cribriform plate shape is plastic and linked to skull shape. Intense artificial selection on domestic dog skull phenotype in the last 200 years has clear effects on secondary features of the domestic dog skull, implying that selection for overt phenotypes also can impact other anatomical features associated with the skull, like the cribriform plate.

Domesticating olfaction: Dog breeds, including scent hounds, have reduced cribriform plate morphology relative to wolves.

The domestic dog is assumed by nearly everyone to be the consummate smeller. Within the species Canis familiaris individual breeds, such as the bloodhound or beagle, are known as olfactory stars. These are "scent breeds," a grouping variably defined as a genetic clade or breed class commonly used for scent detection tasks. Previous work suggests that the dog has a more robust olfactory anatomy than many mammal species. Now we undertake a closer investigation of the dog's olfactory system, both in relationship to its closest wild relatives, the wolf and coyote, and across individual breeds. First, we seek to resolve whether the dog has lost olfactory capacity through its domestication from the wolf lineage. Second, we test the inertial lore that among dogs, "scent breeds," have a superior olfactory facility. As a measure of relative olfactory capacity, we look to the cribriform plate (CP), a bony cup in the posterior nasal cavity perforated by passageways for all olfactory nerve bundles streaming from the periphery to the brain. Using high-resolution computed tomography (CT) scans and digital quantification, we compare relative CP size in 46 dog breeds, the coyote and gray wolf. Results show the dog has a reduced CP surface area relative to the wolf and coyote. Moreover, we found no significant differences between CP size of "scent" and "non-scent" breeds. Our study suggests that the dog lost olfactory capacity as a result of domestication and this loss was not recovered in particular breed groupings through directed artificial selection for increased olfactory facility.