Dental size reduction in the domesticated fox: Implications for the 'domestication syndrome'

Purpose: The "Domestication Syndrome" is an explanatory model for the suite of morphological and physiological traits common across domesticated species. One oft-cited morphological change common to domesticates is a reduction in dental size relative to wild progenitors, yet there are a dearth of studies exploring this dynamic. Moreover, domestication theory has long emphasized that dental size reduction is a byproduct of artificial selection for non-aggressive behavior. The Russian fox domestication experiment provides an untapped source for studying this evolutionary dynamic because it provides a controlled, long term study of selection for non-aggressive behavior and attendant morphological consequences. Yet, the dentition of these experimental foxes has not been heretofore studied. Methods: We employed univariate and multivariate comparisons of maxillary P4, M1, and canine mesiodistal length, buccolingual breadth, and crown height of the canine, as well as mandibular M1 mesiodistal length and buccolingual breadth. These data were collected in sex-balanced samples of the unselected (n=50), tame (n=49), and aggressive (n=50) experimental strains. All measurements were taken directly on macerated, fully cleaned elements using Vernier calipers affording measurement accuracy to 0.05 mm. Results: Consistent with expectations from the 'domestication syndrome' model, tame fox skulls exhibited statistically significantly reduced tooth dimensions in virtually all comparisons relative to both unselected and aggressive strain individuals. Tame-selected foxes also demonstrated more variability in the dentition. Conclusion: These results appear to support domestication hypotheses and highlight the utility of dental evidence as a morphological indicator of reduced aggression.