The Impact of Selection for Facial Reduction in Dogs

Abstract

Through artificial selection, humans have altered the morphology of domestic dogs and produced the broad range of morphological variation seen in modern dog breeds. The purpose of this study was to analyze the effects of artificial selection for short faces in domestic dogs (Canis lupus familiaris). The morphological characteristics associated with years of selection in favor of smushed, paedomorphic faces often result in Brachycephalic Airway Syndrome (BAS), which is characterized by problems with olfaction, respiration, and thermoregulation. We used clinically obtained CT scans of dogs representing brachycephalic breeds (pugs and bulldogs), normocephalic breeds (beagles), and dogs of unknown breed. We established two groups of dogs (brachycephalic and normocephalic) based on cephalic index. In both groups, we recorded a total of 62 cranial and mandibular landmarks. Through geometric morphometric analysis, we determined that the greatest shape variation in this sample was correlated with cephalic index. The shape changes in the crania and mandibles co‐vary, and are both associated with cephalic index. Within the hard palate, the majority of the shape change associated with brachycephaly is centered on the maxilla, specifically at the carnassials. The shape change seen on the hard palate is a unique lateral displacement and rotation of the carnassials, associated with shortening of the hard palate. In contrast, the shape change seen in the mandible is mainly a uniform rostral‐caudal shortening and a medial‐lateral widening. In addition, the soft palate does not appear to be reduced in these breeds. From a functional perspective, the maxillary and mandibular carnassials become malaligned in brachycephalic dogs. The shape change seen in the carnassials demonstrates that morphological integration of the carnassial complex is disrupted in brachycephalic dogs. Despite the facial reduction observed in these breeds, the soft palate does not appear to be reduced, and these soft tissues may crowd the reduced pharyngeal space. Selection for the aesthetic traits associated with brachycephaly in domestic dog breeds results in changes to the carnassial complex and pharynx that are functionally suboptimal and might limit survival outside of a domesticated environment.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.