Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution.

Human activity is drastically altering the habitat use of natural populations. This has been documented as a driver of phenotypic divergence in a number of wild animal populations. Here, we show that urban and rural populations of red foxes (Vulpes vulpes) from London and surrounding boroughs are divergent in skull traits. These changes are primarily found to be involved with snout length, with urban individuals tending to have shorter and wider muzzles relative to rural individuals, smaller braincases and reduced sexual dimorphism. Changes were widespread and related to muscle attachment sites and thus are likely driven by differing biomechanical demands of feeding or cognition between habitats. Through extensive sampling of the genus Vulpes, we found no support for phylogenetic effects on skull morphology, but patterns of divergence found between urban and rural habitats in V. vulpes quantitatively aligned with macroevolutionary divergence between species. The patterns of skull divergence between urban and rural habitats matched the description of morphological changes that can occur during domestication. Specifically, urban populations of foxes show variation consistent with 'domestication syndrome'. Therefore, we suggest that occurrences of phenotypic divergence in relation to human activity, while interesting themselves, also have the potential to inform us of the conditions and mechanisms that could initiate domestication. Finally, this also suggests that patterns of domestication may be developmentally biased towards larger patterns of interspecific divergence.