Selective Breeding in Domestic Dogs: How Selecting for a Short Face Impacted Canine Neuroanatomy

Abstract

Domestic dogs (Canis lupus familiaris) exhibit a wide range of cranial morphologies. This diversity in skull shape is largely the result of modern selective breeding practices. This project investigates the impact of selection for facial reduction on canine neuroanatomy. Previous research has indicated that the breeding for reduced faces in dogs has led to global impacts in the shape of their skull and mandible. This previous research has largely failed to consider, however, the impact of these breeding practices on the soft neuroanatomical tissue. We generated endocasts from an existing set of clinically‐obtained CT scans. This sample consists of a variety of dogs with various cranial morphologies representing four known breeds as well as a comparative sample of dogs of unknown breed. We recorded three‐dimensional coordinate data for 31 landmarks representing various gyri, sulci, and other neuroanatomical landmarks. Placing landmarks at these locations allowed us to analyze differences in shape of the endocasts. Using geometric morphometric analysis, we found that the endocast shape variance in this sample is correlated with cephalic index and as a result, it is clear that selection for facial reduction has caused a perceivable effect on canine neuroanatomy. Furthermore, we found that the majority of the shape variance in the sample was associated with olfactory anatomy. Despite this fact, when the olfactory anatomy‐associated landmarks were excluded from the sample, the rest of the brain morphology was also correlated with cephalic index. The results of this project indicate that modern breeding practices, specifically the selection for dogs with squished faces, have significantly impacted canine neuroanatomy.

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

“…Located on the epithelium of the olfactory turbinals are sensory neurons populated with olfactory receptors, which receive airborne odorants and transmit odor signals via nerve bundles through the cribriform plate to the olfactory bulb of the brain (Evans, 1993). One recent study has shown that artificial selection for short snouts has noticeably impacted the neuroanatomy of these short-faced breeds, and especially the shape of the olfactory bulb (Selba et al, 2021), which is nested in and tightly associated with the cribriform plate (Evans, 1993).…”

Exceptional Changes in Skeletal Anatomy under Domestication: The Case of Brachycephaly

“…One consistent feature of brachycephalic dogs and cats is the shortening of the cranial base and a reduced cranial capacity that can cause overcrowding (i.e., a larger total brain volume relative to body weight) and brain herniation ( Carrera et al 2009 ; Schmidt et al 2013 , 2014 ; Selba et al 2020 ; Sokołowski et al 2020 ). It has been suggested that this volumetric restriction in brachycephalic dogs also leads to a more ventrally rotated longitudinal brain axis, i.e., progressive ventral pitching of the brain, as well as a more ventrally shifted olfactory bulb position ( Roberts, McGreevy and Valenzuela 2010 ; Hussein, Sullivan and Penderis 2012 ).…”

Olfactory detection and discrimination in domestic dogs (Canis lupus familiaris)

“…the length of the cranium is shorter than the width) are worse in olfactory detection than breeds with mesocephalic or dolichocephalic skulls (Polgár et al, 2016), but see (Hall et al, 2015). It has been argued that selective breeding for reduced faces not only resulted in functional anatomical changes in the nose, but in a reduction in brain matter devoted to olfaction and spatial reorganisation of the brain (Selba et al, 2021). While a reduction of olfactory cortical areas clearly impacts the associated functions, such as olfactory detection and discrimination, the impact of spatial reorganisation of the brain areas and associated functions are currently investigated: Anatomical differences between breeds as a result of selective breeding and reflected in the cepahlic index have been reported (Hecht et al, 2019; Selba et al, 2021).…”