Selective breeding in domestic dogs: How selecting for a short face impacted canine neuroanatomy

Abstract

The range of cranial morphology seen in domestic dogs (Canis lupus familiaris) is a direct result of thousands of years of selective breeding. This article is the first to investigate how selection for reduced faces in brachycephalic dogs impacted the neuroanatomy of the canine brain through the analysis of endocasts. Previous research has demonstrated global effects on the shape of the bony cranium as the result of these breeding practices; however, these studies have largely focused on the bony structures of the skull and failed to consider the influence of facial reduction on the soft tissues of the brain. We generated endocasts from an existing set of clinically‐obtained CT scans representing a variety of dogs with various cranial morphologies. These dogs represented four 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 that allowed us to analyze differences in shape of the endocasts. Through geometric morphometric analyses, we determined that the endocast shape variance in this sample is correlated with cephalic index, and thus the selection for facial reduction has caused a perceivable effect on canine neuroanatomy. Additionally, we found the majority of the shape variance in the sample to be associated with olfactory anatomy; however, the rest of the morphology also correlates with cephalic index. The results of this article indicate that modern breeding practices and the selection for dogs with short faces have significantly influenced canine neuroanatomy.

The Olfactory Bulb in Companion Animals—Anatomy, Physiology, and Clinical Importance

“…Anatomic variations in the OB may also be related to the animal's olfactory capacity, which physiologically seems to be linked to the cranial morphology, including the conformation of the lamina cribrosa and the shape and size of the OB that occupies the space over the olfactory fossa [76]. While some studies indicate otherwise [77,78], it is accepted that the brachycephalic breeds have an olfactory acuity and discrimination lower than the other breeds.…”

“…While some studies indicate otherwise [77,78], it is accepted that the brachycephalic breeds have an olfactory acuity and discrimination lower than the other breeds. Although the changes in the nasal cavity itself and the consequent hindering in odorant supply also contribute to a reduced olfaction, the reduction of brain regions related to olfactory discrimination due to compression of the OB and brain in general seem to contribute greatly to this lower olfactory performance [76].…”

Cranial morphology of Balkan and West Asian livestock guardian dogs

“…Nevertheless, the fine characterization of the cranial morphology of many breeds and morphotypes (i.e., groups of dog breeds with common morphological characteristics, hereby based on the ICF classification) has not yet been undertaken. In addition to their functional importance in food intake and vocalization, cranial shape and size have also been related to brain functions and behaviors (Gácsi et al, 2009 ; McGreevy et al, 2004 ), although there are not direct correlations between CI and dog cognition (Selba et al, 2021 ), and the body mass (directly related to cranium size) seems to play a major role in this relationship (Stone et al, 2016 ). Even if only a partial correlation, this relationship between skull size/shape and cognitive abilities is not trivial as dog clubs or councils usually divide dog breeds into groups according to their morphometric appearance, but as well as their daily routines and lifestyles.…”