Scaling of the corpus callosum in wild and domestic canids: Insights into the domesticated brain

Abstract

All domesticated mammals exhibit marked reductions in overall brain size, however, it is unknown whether the corpus callosum (CC), an integral white matter fiber pathway for interhemispheric cortical communication, is affected by domestication differentially or strictly in coordination with changes in brain size. To answer this question, we used quantitative magnetic resonance imaging to compare the midsagittal cross-sectional areas of the CC in 35 carnivore species, including eight wild canids and 13 domestic dogs. We segmented rostro-caudal regions of interest for the CC and evaluated correlations with brain mass. The results of this study indicate that under the influence of domestication in canids, the CC scales to brain size in an allometric relationship that is similar to that of wild canids and other carnivores, with relatively high correlation coefficients observed for all regions, except the rostrum. These results indicate that architectural and energetic considerations are likely to tightly constrain variation in caudal components of the CC relative to overall brain size, however fibers passing through the rostrum, putatively connecting prefrontal cortex, are less constrained and therefore may contribute more toward species-specific differences in connectivity. Given the species diversity of the Canidae and the resurgence of interest in the brain of the domestic dog, further studies aimed at characterizing the neural architecture in domesticated species is likely to provide new insights into the effects of domestication, or artificial selection, on the brain.

Brain of the African wild dog. I. Anatomy, architecture, and volumetrics

“…In addition, we also calculated the cross‐sectional area of the corpus callosum and the cortical gyrification index for each specimen using the approaches detailed in previous studies (see Manger, Hemingway, Haagensen, & Gilisssen, 2010; Manger, Prowse, Haagensen, & Hemingway, 2012; Pillay & Manger, 2007; Spocter et al, 2018; Zilles, Armstrong, Moser, Schleicher, & Stephan, 1989). In Figure 2 we present an outline of the ROI methodology with sample MR images through the brain of the African wild dog.…”

“…Using Phylogenetic Generalized Least Squares (PGLS) regression analysis we quantitatively compared the average values for the African wild dog with allometric data obtained from a subset of other mammals used in previous studies by our group (Grewal et al, 2020;Manger et al, 2010Manger et al, , 2012Maseko et al, 2011Maseko et al, , 2012Patzke et al, 2015;Pillay & Manger, 2007;Spocter, Uddin, et al, 2018). Our goal here was not to re-evaluate the published data but rather to show through superimposition where the average values for the African wild dog are found in relation to other mammals.…”

Brain gyrification in wild and domestic canids: Has domestication changed the gyrification index in domestic dogs?

“…Although limited in scope, recent allometric analyses have suggested that domestic dogs (i.e., golden retriever) might possess a larger number of cortical neurons when compared with other larger‐brained carnivores (Jardim‐Messeder et al, 2017). Spocter et al (2018) recently reported increased variability in canine corpus callosum morphology and demonstrated that amidst the general pattern of conservation in corpus callosum proportions among the canids, there still remained evidence of breed‐specific patterning in dogs, likely influenced by artificial selection. More recently, Hecht et al (2019) provided additional evidence for the influence of artificial selection on canine brains through observations of breed‐specific specializations in brain networks.…”

Neuromorphological changes following selection for tameness and aggression in the Russian fox-farm experiment

“…These latter measurements revealed links with individual variation in behavior, including in brain regions that did not show volumetric differences, notably, the hypothalamus. Additionally, Network 3 consisted primarily of the hypothalamus and prefrontal cortex, two regions strongly implicated in both fox and dog domestication [8][9][10][19][20][21][30][31][32][33] . In this network, factor loadings did not differentiate the tame from aggressive strains; rather, the selectively-bred strains together were differentiated from the conventional strain ( Figure 3C).…”