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.
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.
Highly elongate body plans have evolved multiple times in the Actinopterygii, and members of many of these groups are known to use lateral undulation on land. Here, we quantified components of the axial skeleton for four phylogenetically disparate actinopterygian fishes and one sarcopterygian to determine whether axial morphology may affect their locomotor kinematics. We tested species in water and on two terrestrial substrates: loose wet pebbles and wet sand. Differences in axial morphology translated to differences in wavelengths, amplitudes, and frequencies at the center of the body and tail while swimming, but overall, we consistently observed a similar shift in kinematic patterns when fish were moving on the two terrestrial treatments. Generally, our kinematic data support our hypothesis that elongate fishes increased their wave frequency and shorten their wavelengths on terrestrial substrates but we also observed lower wave amplitudes contrary to our prediction. As anticipated, animals exhibited a higher distance ratio (DR), our metric of locomotor efficiency, at the head, center of the body, and tail in aquatic trials. DRs were between 25% and 50% higher in water compared to terrestrial treatments. Locomotion was less effective on wet sand substrate compared to loose wet pebble substrate as exhibited by the discrepancy in DRs and wave patterns along the fish. These data suggest that loose wet pebble substrates do indeed provide vertical points for lateral force transmission and that highly elongate fish have an advantage when moving along this substrate. Our species varied greatly in their total vertebral numbers, 93–129, and in their proportion of precaudal (42–102) and caudal vertebral numbers (10–64). Therefore, despite major differences in vertebral proportions, we find that fishes with anguilliform body plans share similar suites of kinematic patterns within aquatic versus terrestrial treatments and that a pebble substrate can better facilitate axial movements.
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