Morphology does not covary with predicted behavioral correlations of the domestication syndrome in dogs

Abstract

Domesticated animals display suites of altered morphological, behavioral, and physiological traits compared to their wild ancestors, a phenomenon known as the domestication syndrome (DS). Because these alterations are observed to co‐occur across a wide range of present day domesticates, the traits within the DS are assumed to covary within species and a single developmental mechanism has been hypothesized to cause the observed co‐occurrence. However, due to the lack of formal testing it is currently not well‐resolved if the traits within DS actually covary. Here, we test the hypothesis that the presence of the classic morphological domestication traits white pigmentation, floppy ears, and curly tails predict the strength of behavioral correlations in support of the DS in 78 dog breeds. Contrary to the expectations of covariation among DS traits, we found that morphological traits did not covary among themselves, nor did they predict the strength of behavioral correlations among dog breeds. Further, the number of morphological traits in a breed did not predict the strength of behavioral correlations. Our results thus contrast with the hypothesis that the DS arises due to a shared underlying mechanism, but more importantly, questions if the morphological traits embedded in the DS are actual domestication traits or postdomestication improvement traits. For dogs, it seems highly likely that strong selection for breed specific morphological traits only happened recently and in relation to breed formation. Present day dogs therefore have limited bearing of the initial selection pressures applied during domestication and we should reevaluate our expectations of the DS accordingly.

Brain Size Does Not Rescue Domestication Syndrome

“…The null hypothesisthe degree of phenotypic change expected between similarly genetically differentiated populations in the absence of domesticationhas rarely if ever been defined. A recent large-scale study failed to find the covariation between morphology and behavior expected if the domestication syndrome were real [16]. Although it is a long-standing hypothesis, the domestication syndrome has not yet been rigorously tested, as any scientific hypothesis must be, and cannot be assumed to be true.…”

Domestication constrains the ability of dogs to convey emotions via facial expressions in comparison to their wolf ancestors

“…Domestication has resulted in the morphologies of many species diverging greatly from that of their wild, ancestral counterparts 72 , 73 . As a result, domesticated mammals generally possess a range of morphological traits that visibly distinguish them from their wild counterparts, in particular elements of head allometry 72 , 73 .…”

Cranial volume and palate length of cats, Felis spp., under domestication, hybridization and in wild populations

“…While a growing body of research (e.g. red junglefowl Gallus gallus [ 27 ], village dogs Canis familiaris [ 28 ] and foxes Vulpes vulpes [ 29 ]) is in line with the neural crest cell hypothesis, the hypothesis has been challenged by others [ 10 , 11 , 30 ]. Our results on cranial volume reduction in domestic cats are in line with the neural crest cell hypothesis and previous reports [ 1 , 31 ], but we did not find a reduction in snout length, which fails to uphold the prediction of this hypothesis.…”