Domestication effect on skull morphology and biting performance in rats

BECERRA FEDERICO; BEMMANN MAXIMILIAN; CAGAN ALEXANDER; KONOSHENKO MARIYA; KOZHEMYAKINA RIMMA; KUPCZIK KORNELIUS

North Bethesda

Congreso; International Congress of Vertebrate Morphology; 2016

Interantional Society of Vertebrate Morphology

Domestication of wild animals has been a key factor in the development of human civilizations. It enabled the development of more suitable food resources, modes of transportation, companionship and even enhanced group defense against potential threats. This practice has resulted in a wide variety of breeding lines differentiated by their differences in morphology, physiology, gene expression and behavior. Here, in vivo incisor biting performance and skull morphology were tested in 4 months old male and female gray rats Rattus norvegicus, originating from two wild derived breeding lines selected for aggressive and tame behavior, respectively, towards humans for over 70 generations. We focused on the aggressive and intercross (aggressive*tame) lines, totaling 39 individuals. Body size, head length and mandibular width all showed clear sexual dimorphism, with males always being larger than equivalent females. Considering inter-line comparisons, no significant difference was found in any size measurement in either males or females, except for aggressive males having larger heads than intercross males. Contrary to the morphological data, within breeding lines females produced stronger bites than males. Once the body size effect was removed, bite force was (poorly) predicted by mandibular width, and only in aggressive males. Thus, beyond their behavior, genetics and physiology, the long-term domestication process resulted in smaller head size in the least aggressive rats while overall body size remained relatively similar. Yet, our results on biting performance cannot be attributed to differences in body or head size. They might offer additional evidence of the dimorphic aggressive behavior in female rats associated with maternal care and social structure, which has been observed in gregarious wild rodents.