Schultz’s rule in domesticated mammals

Abstract

Schultz’s rule predicts early eruption of replacement teeth (incisors, canines, and premolars) relative to molars as growth slows and life history events take place over a greater span of time. Here, we investigate if the opposite trend might occur during the domestication process as a consequence of an accelerated life-history and driven by increased energetic needs. We provide new data on tooth eruption in four mammalian species and their domesticated forms: wolf and dog, polecat and ferret, bezoar and goat, wild boar and pig. Our results show some variation in eruption sequences between wild and domestic forms, but none that is consistent and reliably distinct from intraspecific variation. There may be variation in the absolute timing of dental eruption, but despite well documented changes across life history variables, which distinguish wild from domestic forms, eruption sequences remained constant in each wild and domestic version of the species we examined. A conserved eruption sequence is in accordance with many earlier studies, which found no evidence for Schultz’s rule in some wild clades of mammals. Phylogenetic conservation and functional factors likely play an important role in constraining patterns of growth and tooth eruption in these mammals. Furthermore, we suggest that the domestication processes started too recently for fundamental changes of tooth eruption sequences to occur.